eDSBS Abstracts

Ecosystem-based modeling is rapidly becoming a foundational technique to assess the health and stability of ecosystems, yet few models address the deep-pelagic realm. Globally, mesopelagic assemblages are threatened by anthropogenic stressors (e.g., commercial fishing, oil exploitation, noise, proposed seafloor mining), but the effect of these impacts on this ecosystem are currently unknown. Micronekton are the primary consumers of oceanic zooplankton production, and are prey of apex oceanic predators, suggesting community-scale disturbances will affect the trophic structure of the entire pelagic ecosystem. We have developed an ecosystem-based model for the offshore (waters deeper than 1000 m) Gulf of Mexico using data collected between 2011-2018, and tracked the top-down and bottom-up impacts that each functional group had on the others. These trends are assessed to examine whether interactions between assemblage components has changed directionally over time. Zooplankton (trophic level = 2) represent greater than one-third of the total system biomass and also 40% of the total energy throughput in the system. Following a decline in micronekton biomass that simulates empirical observations, approximately 27% of the possible functional group interactions showed significant changes from 2011-2018. Direct top-down interactions changed more frequently than direct bottom-up and indirect trophic relationships. In many instances involving apex predators, when one interaction strengthened another weakened, indicating an ability for predators to shift diet according to prey availability. As apex predators shifted diet, the role of micronekton in defining the trophic structure of the system was minimized, while consumption of juvenile conspecifics of commercial species increased. The predation pressure exerted on micronekton groups did not decline during the simulation, a factor that likely inhibits population-level recovery of the assemblage.

Itay Budin, University of California San Diego; Steven H.D. Haddock, MBARI

In deep-sea organisms, the fluidity of lipid membranes is adaptively tuned to maintain cellular integrity at ambient temperature and pressure. Classic studies report direct correlations between cold habitats, deep habitats, and membrane-fluidizing lipid compounds in fish and microbes, but little has been done to isolate the effects of temperature and pressure on the lipid pool. To address the difference between depth- and cold-adaptation of membranes, we measured fatty acid compositions of 124 ctenophores, spanning all four taxonomic orders, depths from sea level to 4000 meters, and temperatures from -2° to 25° C. Thanks to the incredible taxonomic and habitat diversity of phylum Ctenophora, we identified fatty acid profiles related specifically to depth and to temperature. This finding informs requirements for invertebrate lineages colonizing the deep sea, and may also be relevant to midwater trophic ecology, since several of the profiled fatty acids are dietarily essential.

Rachael Peart, National Instiute of Water & Atmospheric Research; Heather Ritchie, Japan Agency for Marine-Earth Science and Technology ; Heather Stewart, British Geological Survey; Stuart Piertney, University of Aberdeen; Thomas Linley, Armatus Oceanic; Alan Jamieson, Newcastle University

Our understanding of the ecology of the hadal zone (> 6000 m depth) is based solely on subduction trenches, leaving other geomorphological features at hadal depths, such as fracture zones, troughs, and basins, understudied. The Wallaby-Zenith Fracture Zone (WZFZ) in the East Indian Ocean offers a unique location to compare and contrast species distribution and community structure in a non-subduction hadal feature with deep ocean trenches. The scavenging amphipods were collected using free-fall baited landers from the six depths between 4932 to 6546 m. Eleven species were identified across the abyssal-hadal transition zone using a paired morphological and DNA barcoding approach, with two species newly described as Stephonyx sigmacrus and Civifractura serendipia Weston, Peart, Jamieson 2020. The community composition was found to change gradually from abyssal to hadal depths consistent with an ecocline, which contrasts with the ecotone shift characteristic of subduction trenches. Bathycallisoma schellenbergi (Birstein & Vinogradov, 1958) was the dominant species at depths greater than 6500 m but did not display the patterns of ontogenetic vertical stratification consistently found in hadal trenches. Additionally, genetic differentiation was detected between the B. schellenbergi population in the WZFZ and four previously sampled Pacific Ocean trench populations, indicating these features are not interconnected through ongoing gene flow. Combined, these data indicate that some hadal fauna have far broader distributions than previously understood, with populations present in both hadal subduction trenches and non-subduction fracture zones and basins interspersed across the abyssal plains. This initial exploration highlights that while non-subduction features are an overlooked minor fraction of the total hadal area, they are essential to our understanding of the ecological and evolutionary dynamics across the hadal zone.

Rachael Peart, National Institute of Water & Atmospheric Research; Alan Jamieson, Newcastle University

The Wallaby-Zenith Fracture Zone, within the Wharton Basin of the East Indian Ocean, is a geomorphologically complex structure with depths from abyssal to hadal (∼6600 m) with limited published taxonomic data. To fill this knowledge gap, this study describes two new species of scavenging amphipods, Stephonyx sigmacrus sp. nov. (Uristidae) and Civifractura serendipia gen. et sp. nov. (Alicellidae), collected using baited traps from a depth of 4932 m. As identification of deep-sea amphipods is challenged by phenotypic plasticity and convergent evolution, we combined a morphological with a molecular phylogenetic analysis of two mitochondrial (16S rDNA and COI) and two nuclear (Histone 3 and 28S rRNA) regions, where possible (no genetic material was obtainable from S. sigmacrus sp. nov.). The genetic data uncovered cryptic taxonomy and elevated diversity within the non-monophyletic Alicellidae family and provided evidence for establishing a new genus. These investigations highlight the application of integrative taxonomic approaches and represent a potential model for resolving incongruent morphological and molecular phylogenies for deep-sea amphipods and other specimen-limited taxa.

Santiago Herrera, Lehigh University ; Erik Cordes, Temple University

Lophelia pertusa is among the most abundant and wide-spread deep-sea corals and acts as the foundation for deep-sea ecosystems. These organisms are under increasing anthropogenic threat, including global ocean change and oil extraction. Here, we analyze the gene expression patters from L. pertusa colonies exposed to oil and dispersant mixtures under current and future conditions (temperature: 8°C and 12°C, pH: 7.9 and 7.6). The phenotypic health ratings showed that regardless of environmental condition, average health significantly declined during 24-hour exposure to dispersant alone but was not significantly altered in the other treatments. Temperature and pH did not show a significant impact on coral health at the 24-hour exposure timepoint. However, increased temperature (12°C) resulted in a delay in recovery from dispersant exposure. A Weighted-Gene Correlation Network Analysis (WGCNA) identified networks of co-expressed genes in response to the exposure treatments (control, oil, dispersant, and oil + dispersant). The WGCNA identified a network of 2,526 genes that were upregulated in response to oil and downregulated in response to dispersant. Gene Ontology (GO) analysis of this network revealed that these genes are involved in metabolic process, regulation of gene expression, and organelle organization. Also, three networks of genes (2,770 genes total) were down regulated in the control and oil exposures but upregulated in response to dispersant. The GO analysis for these three networks revealed processes involved in the response to stress, immune system function, cellular and developmental wound healing, and more. These analyses allow us to identify the underlying molecular processes that contributed to the effects observed when the corals were exposed to dispersant alone and investigate the molecular underpinning leading to the delay in recovery observed under increased temperature.

Andrew F. Hugall, Museums Victoria; Timothy D. O'Hara, Museums Victoria

The deep ocean is the largest biome on Earth and yet it is among the least studied environments of our planet. Life at great depths requires several specific adaptations, however their molecular mechanisms remain understudied. We examined patterns of positive selection in 416 genes from four brittle star (Ophiuroidea) families displaying replicated events of deep-sea colonization (288 individuals from 216 species). We found consistent signatures of molecular convergence in functions related to protein biogenesis, including protein folding and translation. Five genes were recurrently positively selected, including CCTα (Chaperonin Containing TCP-1 subunit α), which is essential for protein folding. Molecular convergence was detected at the functional and gene levels but not at the amino-acid level. Pressure-adapted proteins are expected to display higher stability to counteract the effects of denaturation. We thus examined in silico local protein stability of CCTα across the ophiuroid tree of life (967 individuals from 725 species) in a phylogenetically-corrected context and found that deep sea-adapted proteins display higher stability within and next to the substrate-binding region, which was confirmed by in silico global protein stability analyses. This suggests that CCTα not only displays structural but also functional adaptations to deep water conditions. The CCT complex is involved in the folding of ~10% of newly synthesized proteins and has previously been categorized as ‘cold-shock’ protein in numerous eukaryotes. We thus propose that adaptation mechanisms to cold and deep-sea environments may be linked and highlight that efficient protein biogenesis, including protein folding and translation, are key metabolic deep-sea adaptations.

Alan Friedlander, National Geographic Society, Pristine Seas; Richard Pyle, Bernice P. Bishop Museum; Cassandra Brooks, University of Colorado Boulder, Environmental Studies Program; Kristina Gjerde, International Union for the Conservation for Nature, Global Marine and Polar Programme

Coral reefs are widely regarded as one of the top science and conservation priorities globally, as previous research has demonstrated that these ecosystems harbor an extraordinary biodiversity, myriad ecosystem services, and are highly vulnerable to human stressors. However, most of this knowledge is derived from studies on nearshore reefs, with coral reefs remaining largely unstudied in marine areas beyond national jurisdiction (ABNJ), commonly known as the high seas. We provide an overview of what is currently known about coral reefs on the high seas from a variety of publicly-available datasets, as well as discuss the challenges of protecting marine biodiversity in ABNJ. Despite the fact that the terms “coral reef” and “high seas” are rarely combined in the same sentence, there is compelling evidence that extensive coral reef habitat exists in many ANBJ locations, the vast majority of which is unprotected and under threat from various human stressors, including overfishing, climate change, pollution, and impending seabed mining. High seas coral reefs not only provide enormous opportunities for future scientific explorations and discovery, but should also be prioritized for future conservation efforts since they harbor unique biodiversity and are particularly fragile.

Joan M. Alfaro-Lucas, Ifremer; Mari H. Eilertsen, Department of Biological Sciences, University of Bergen; Oliver S., Ashford; OceanMind

Characterising the global distribution, composition and relationship of species occurring in chemosynthesis-based ecosystems (CBEs) at both regional and global scales will greatly help to advance research and conservation efforts in these environments. The most recent data compilation on the distribution of species occurring at and around hydrothermal vents, cold seeps and organic falls (ChEssBase) was in 2010, and since then only sporadic updates have been made. In response to this, we have begun compiling a new global, open-source database, ‘MACROCHESS’, which aims to incorporate over a decade of discoveries, the most recent taxonomic knowledge for meio-, macro- and megafauna occurring on CBEs, and detailed environmental metadata. We envision that MACROCHESS will be directly applied in the investigation of CBE biogeography and ecology, and in conceiving, strategising and guiding future international research, collaborations, management and conservation efforts, while functioning as a unified platform for depositing biological data. Possible research avenues that this database may help to facilitate include investigating i) the response of CBEs to environmental change and human disturbance, ii) the impacts of biodiversity loss on the ecosystem services provided by CBEs and iii) clues as to the evolution of species occurring at CBEs. Here, we will present MACROCHESS to the wider deep-sea community, report progress regarding the different phases of its on-going construction, highlight the different components of the database, and illustrate some preliminary results and knowledge gaps based on a data compilation across 280 vent, 88 organic fall and 33 seep localities.

Jeffrey Drazen, University of Hawai'i

Interest in deep-sea mining for minerals and rare-earth metals is growing as demands for these resources are increasing, and these demands may not be met by terrestrial sources alone in the future. Deep-sea mining would be a complex operation, with different impacts on the biology and environment at different spatial and temporal scales. The impacts may also extent to other industries, such as the high-seas fishing industry. It is currently unknown how deep-sea mining practices and high-seas fisheries would intersect, and how countries may be impacted if mining practices do affect fishery catches. A first approximation can be obtained by investigating how mining areas overlap with fishery catches in space, and more specifically, how the catches from mining areas compare to catches from Regional Fisheries Management Organization (RFMO) areas or oceanic catches. Here, we investigate the fishery catches of six mining areas for which the ISA has released exploration licenses. We show the importance of considering the intersection at a site- and country-specific level, as there are differences in catches between mining sites and RFMO or ocean catches for different countries. While most countries’ catches from mining areas are small, there are several nations, including developing nations, which can have large proportions of their total and total tuna catches coming from mining areas. We show how the potential spread of impacts away from mining areas changes the intersection between fishing and mining, and how that changes the contribution of mining-area catches to RFMOs or oceanic catches for different countries. These results provide a first step to highlight how these two high-seas industries may intersect and potentially affect each other. The impacts of deep-sea mining on biology, environment and existing industries should be considered in the context of ongoing stressors in the high seas, such as climate change and overexploitation.

Marjolaine Matabos, Ifremer, REM/EEP/LEP; Jonathan Drugmand, Ifremer, REM/EEP/LEP and Université catholique de Louvain, Ecole de biologie; Agathe Laës, Ifremer, REM/RDT/LDCM; Pierre-Marie Sarradin, Ifremer, REM/EEP/LEP; Jozée Sarrazin, Ifremer, REM/EEP/LEP

At hydrothermal environments, free-living microorganisms may be an essential food source to the non-symbiotic macrofauna, dominated by bacterivorous species (Portail et al., 2018) and may act as source populations for transmitting symbionts to Bathymodiolus mussels (Won et al., 2003). At the Lucky Strike vent field (LS), on the Mid-Atlantic Ridge (MAR), filamentous microbial mats are dominated by thiotrophic Beggiatoa spp., along with other bacterial and archaeal species (Crépeau et al., 2011). These mats cover various substrata (Cuvelier et al., 2009) and are abundant in low-temperature habitats (<10°C; Barreyre et al., 2014). However, their local distribution and role on the functioning of vent communities remain to be elucidated. Using images collected between 2012 and 2019 by the TEMPO observation module, connected to the EMSO-Azores observatory (EMSO-ERIC, www.emso-fr.org/fr/EMSO-Azores), we examined the temporal dynamics of microbial mats on the active Eiffel Tower edifice at LS. We surveyed an area (1.5m²) of bare substratum occupied by Bathymodiolus azoricus and zoanthid assemblages and under the influence of a small diffuser. Microbial mats developed preferentially 1m away from the fluid exit, alongside B. azoricus assemblages and on unidentified mineral deposits. Globally, microbial mat surface increased near the fluid exit in 2015-2019 compared to 2012-2015. No significant periodicity was detected on daily annotations of microbial mats. Microbial mat cover also exhibited infra-annual changes, alternating abruptly from absence to development periods within a few months, despite stable temperatures (<10°C). We hypothesised that in addition to biotic interactions, other factors such as local deviation of fluids and the type of substratum could affect the positioning of the microniches available for microbial mat communities. Further studies are needed to gain knowledge on the composition of these mats and the factors shaping their small-scale distribution.

Sophie Cannon, University of Southampton; Sarah DeLand, Duke University; James Delgado, SEARCH Inc.; David Eltis, Emory College of Arts and Sciences; Patrick Halpin, Duke University; Michael Kanu, Republic of Sierra Leone Permanent Mission to the United Nations; Charlotte Sussman, Duke University; Ole Varmer, The Ocean Foundation; Cindy Van Dover, Duke University

More than 12.5 million Africans were held captive on 40,000+ voyages during the transatlantic slave trade. Many did not survive the voyage and the Atlantic seabed became their final resting place. Contemporary poetry, music, art and literature portray the meaning of the Atlantic seabed to descendants of those who were held captive, but the cultural heritage of the Atlantic seabed has yet to be formally recognized by the International Seabed Authority (ISA), which governs mineral rights to the Atlantic seabed in Areas Beyond National Jurisdiction (ABNJ). Member States of the ISA have a duty to protect underwater cultural heritage. We encourage these States to consider ways to commemorate those who lost their lives and came to rest on the seabed, in advance of mineral exploitation. Commemoration may occur without limiting access to mineral resources. We suggest that one or more virtual ribbons marking major slave-trade routes across the Atlantic should be depicted on ISA maps in commemoration of those who died during their Middle Passage.

Mark Shepherd, Queen's University Belfast; Julia Sigwart, Queen's University Belfast; Geoff McMullan, Queen's University Belfast; Robert Graham, Queen's University Belfast

Deep-sea hydrothermal vents house many highly specialised taxa adapted to life in an extreme environment and chemosynthetic energy sources, none more so perhaps than the peltospirid gastropod Gigantopelta chessoia C. Chen, Linse, Roterman, Copley & Rogers, 2015. Restricted to hydrothermal vents on the East Scotia Ridge, this gastropod is giant relative to other members of the family, a feature that may be attributable to adaptations to host internal symbionts. Individual G. chessoia house chemoautotrophic bacterial endosymbionts in an enlarged, specialised organ adapted from the oesophageal gland, known as the trophosome. This organ grows after larval settlement and metamorphosis, in a final ‘cryptometamorphosis’ to the holobiont life stage. This adaptation is key to the success of the species, yet very little is known about the relationship of the host snail and its symbionts. With the recent advancement in molecular ‘omics’ techniques, there is now an opportunity to understand the mechanisms that underpin successful holobiont relationships through the characterisation and quantification of biological molecules. This study therefore aims to employ profiling proteomics techniques to analyse the protein expression of G. chessoia and its associated bacterial symbionts to provide new insights into host-symbiont interactions, specialised physiological mechanisms, and biochemical responses in this holobiont. Using proteomics to explore the physiological relationship between host and symbiont will improve our understanding of the complex relationships that underpin the success of organisms endemic to hydrothermal vents.

Hiroki Taninaka, Interdisciplinary Graduate School of Agriculture and Engineering, University of Miyazaki; Masanori Nonaka, Okinawa Churashima Foundation Reseach Center; Fumihito Iwase, Shikoku Marine Life Laboratory; Taisei Kikuchi, Parasitology, Faculty of Medicine, University of Miyazaki; Yoshihisa Suyama, Field Science Center, Graduate School of Agricultural Science, Tohoku University; Satoshi Nagai, Japan Fisheries Research and Education Agency, National Research Institute of Fisheries Science; Nina Yasuda, Graduate School of Agriculture, Faculty of Agriculture, University of Miyazaki

Precious corals known as coralliid corals (Anthozoa: Octocorallia) play an important role in increasing the biodiversity at a depth of at least 100m except for in the Mediterranean Sea. Currently, these corals are highly threatened because of overfishing that has been brought on by an increased demand and elevated prices for them. To effectively conserve precious coral species, species delimitation is important, since species is the basic unit for conservation and legal regulation such as CITES. Examining genetic structures of intra-species is also crucial because coral populations are mutually connected via larval dispersal. However, the species status of Pleurocorallium konojoi and P. elatius has been doubted because traditional genetic markers could not discriminate the two species. In addition, no genetic marker has been available to reveal genetic structures of the three typical precious corals (Corallium japanicum, P. konojoi and P. elatius) in Japan to estimate meta-population structure. We first applied MIG-seq analysis for P. konojoi and P elatius samples collected from Okinawa to Shikoku areas in Japan to examine species boundaries. STRUCTURE and PCoA using 223 SNPs revealed they are different species without admixture. Secondly, we used samples of the two species (C. japanicum and P. konojoi) collected from southwestern Shikoku in Japan to examine and compare genetic structure. We analyzed genetic diversity and FST based on 478 SNPs. C. japanicum populations indicated stronger genetic structuring and limited larval dispersal than P. konojoi. Our results suggest the following conservation implications 1) P. elatius and P. konojoi should be conserved separately. 2) recovery of damaged C. japanicum populations via larval supply from other populations would be more limited and more difficult than that of P. konojoi.

Pilar Ríos, IEO Santander; Alex Mitchell, The Natural History Museum of London; Shuangqiang Wang, DFO Canada; Andrew Davies, University of Rhode Island; Ellen Kenchington, DFO Canada; Alex Cranston, The Natural History Museum of London; Katrhin Busch, GEOMAR; Vanina Tonzo, Estación Biologógica Doñana; Paco Cárdenas, Uppsala University; Carlos Leiva, Universitat de Barcelona; Vasiliki, Koutsouveli, The Natural History Museum of London; Javier, Cristobo, IEO Gijón; Ute, Hentschel, GEOMAR; Hans Tore, Rapp, University of Bergen; Jim, Drewery, Marine Scotland Science; Maria Belén, Arias, The Natural History Museum of London; Ana, Riesgo, The Natural History Museum of London

Northeast Atlantic deep-sea sponge grounds are crucial components of the regional marine fauna. To properly develop effective conservation plans, it is crucial to understand the genetic diversity and molecular connectivity patterns at the population level of the species involved. We present the study of three congeneric sponges of the genus Phakellia using multiple sources of evidence. We used ddRADseq derived SNPs to investigate genetic diversity and scales of connectivity among P. ventilabrum populations across the Northeast Atlantic Ocean. The ca. 3,000 neutral SNPs obtained for 166 individuals indicated panmixia among samples from the Rockall Bank to the Schulz Bank (Greenland Sea), despite samples spanning 2,500 km and some of them occurring at quite different depths. We also observed significant genetic distance between samples from the Cantabrian Sea and Roscoff with the remainder of the sites. Genetic panmixis and structure in P. ventilabrum is explained by the prevalent oceanic currents, which we corroborated using the BNAM oceanographic model and a 3D particle-tracking algorithm. As for P. robusta and P. hirondellei, our phylogenetic analysis using COI placed these species as sister. Haplotype networks using COI revealed that P. robusta showed a clear genetic structure separating deep-water samples from the Cantabrian Sea and the Hatton-Rockall Basin, from shallow-water samples. The ca. 800 SNPs obtained for 23 P. robusta specimens segregated samples by bathymetry rather than by distance, and detected a predominant northwards migration for shallow-water specimens connecting sites separated ca. 2,000 km, probably due to prevalent oceanographic currents. Our analysis combining the datasets of the P. robusta and P. hirondellei revealed the presence of potential hybrids, which was corroborated by morphological and microbial analyses. We discuss the importance of using NGS techniques to unveil hybridization and the implications of our results for conservation.

Jon Moore, Honors College, Florida Atlantic University; April Cook, Nova Southeastern University; Andrea Bernard, Nova Southeastern University; Ron Eytan, Texas A & M University Galveston; Mahmood Shivji, Nova Southeastern University; Rosanna Milligan, Nova Southeastern University; Dante Fenolio, San Antonio Zoo

As of 2009, the total number of fish species known in the Gulf of Mexico (Gulf hereafter) was 1541. At the conclusion of the DEEPEND program in Jun 2020, researchers have identified 897 species from offshore sampling, of which 186 are new records for the Gulf, and 21 putatively new to science. Thus, one in ten fish species now known in the Gulf is derived from DEEPEND deep-pelagic research. This number is a function of: 1) intensive, multi-mode pelagic sampling, from the surface to 1500 m depth; 2) rigorous taxonomic analysis, integrating morphological and molecular taxonomy; and 3) the unique ecotonal, quasi-oligotrophic, and oxygenated nature of the deep Gulf itself. Each of these functions will be described in detail. Functionally, 4% of these fish species are primarily epipelagic, 33% mesopelagic, 7% meso/bathypelagic (spanners), 13% bathypelagic, 25% coastal juveniles, and 18% benthic/demersal juveniles. Of the latter, the diversity of larval benthic eels was remarkable, with 111 species (vs. seven species of truly pelagic eels). Numerous lines of research have revealed an extremely high degree of vertical connectivity in the pelagic Gulf, indicating that this oceanic ecoregion should be viewed as one large, integrated unit from the surface to great depths rather than a series of stacked biomes. Given these data and the trend of rapidly expanding resource extraction in the deep Gulf, there is an immediate need for informed stewardship of this exceptional ecosystem.

Lupita Bribiesca-Contreras, Natural History Museum; Thomas Dahlgren, University of Gothenburg; Helena Wiklund, Natural History Museum; Sergio Taboada, Natural History Museum ; Adrian Glover, Natural History Museum

The Clarion-Clipperton Zone (CCZ) has become an area of commercial importance due to the growing interest in mining high-grade polymetallic nodules. Several environmental baseline surveys have been carried out to assess the biodiversity and community structure of meiofauna, megafauna, macrofauna, and microbes within different exploration contract areas, and adjacent APEIs (Areas of Particular Environmental Interest). However, it is crucial to understand patterns of biodiversity, species ranges, and connectivity across the entire CCZ, as this will allow assessing the current spatial conservation strategy and to better predict the potential impacts on biodiversity due to mining. Annelids represent one of the most abundant and diverse macrofauna groups in abyssal soft muds, including the abyssal plains of the CCZ, hence they have been the target of several studies. However, investigating patterns of polychaete beta diversity in the CCZ has been hindered by taxonomic uncertainty. Many samples lack species identification as they belong to new undescribed species, or owing to the loss of fragile morphological characters during sampling. This therefore makes different diversity studies incomparable. Here, we investigate patterns of beta diversity for polychaetes in the CCZ using published and unpublished genetic information (cytochrome c oxidase subunit-I, COI; and 16S) from 1998 polychaetes collected across six exploration licence areas, and one APEI (APEI-6) during different surveys. Compositional, phylogenetic, and functional beta diversity are estimated to characterise regional diversity patterns of polychaetes in the CCZ and to provide new insights into the processes driving diversity on abyssal seafloors.

Chris Yesson, Institute of Zoology

The Nephtheidae are a widely distributed family of Alcyonacean corals, found in cold waters at depths below 50m. In the Northwest Atlantic, nephtheid species commonly form dense communities harbouring high biodiversity, which are recognised as vulnerable marine ecosystems. Increased pressure from deep-sea fisheries around Greenland has been shown to have significant negative effects on nephtheid diversity and biomass. However, the underlying genetic structure of these populations is unknown. This study presents 22 novel single nucleotide polymorphism (SNP) markers which were used to assess the population structure of Nephtheidae corals across the east, south, and west coasts of Greenland. Population genetic patterns across the area were analysed using discriminate analysis of principle components (DAPC). Significant genetic differentiation (Fst) was found between all regional groups analysed, with no significant pattern of isolation by distance (IBD) or isolation by depth. Genetic cluster assignment appears to be species specific, and suggests that these SNP markers can be used for species delimitation within this family which has traditionally represented a taxonomic challenge. Hypotheses are presented to explain variation in Fst and IBD results, and potential species-specific patterns of gene flow. The genetic tools developed here provide a foundation for further studies of nephtheid species. Understanding the population structure, reproductive behaviour, and dispersal capacity of deep-sea species is crucial to the designation of suitable management strategies around Greenland. These results represent an important step in elucidating the population structure of these habitat-forming species, and determining how they can best be protected from increasing anthropogenic threats.

Nico Fassbender, Nekton Foundation; Sara Winter, Nekton Foundation; Kaveh Samimi-Namin, University of Oxford, Department of Zoology; Sheena Talma, Nekton Foundation; Lucy Woodall, University of Oxford, Department of Zoology

Indian Ocean coral reef ecosystems are one of the least explored, least funded and least protected reefs worldwide. The “First Descent: Seychelles” expedition in 2019 sought to address that gap by exploring reef habitats in seven remote coral atolls across the Exclusive Economic Area of Seychelles, a Large Ocean State located just south of the equator in the Western Indian Ocean. A combination of divers, submersibles and remotely operated vehicles were deployed between 10-350m to investigate the biodiversity and connectivity patterns of benthic and demersal fish communities across depth and location. Preliminary results indicate distinct faunal and floral groupings across depth, corresponding to biological depth zonation patterns reported from other (sub)tropical locations across other ocean basins. There was great variability between atolls likely related to unique local conditions (e.g. topography, hydrodynamic regime) as well as level of management and protection status. Since the majority of reefs in the Indian Ocean, including those of Seychelles, have never been systematically explored beyond recreational SCUBA depths (i.e. 30m) before, it is expected that the resulting datasets from this expedition will provide important baseline information on the status of deeper reef ecosystems across the region, which will be of value to existing, ongoing and future marine spatial planning exercises of Indian Ocean coastal states.

Andrew Gooday, National Oceanography Centre; Teresa Radziejewska, University of Szczecin, Szczecin, Poland; Brygida Wawrzyniak-Wydrowska, University of Szczecin, Szczecin, Poland; Pedro Martinez Arbizu, Senckenberg German Center of Marine Biodiversity, Wilhelmshaven, Germany

In April 1995, sediment at an abyssal site in the eastern part of the Clarion-Clipperton Zone (CCZ, subequatorial NE Pacific) was experimentally disturbed to produce and study effects mimicking those generated by nodule mining. In April 2015, during RV SONNE cruise SO 239, sediment samples were collected from three zones within the test site: impacted (tracks left in the sediment by the disturbing device); re-sedimented (the adjacent area covered by re-deposited sediment stirred up by the disturbance); and control (the unimpacted area). We examined macrofauna-sized (>250 µm) benthic foraminifera present in the uppermost sediment layer (0-1 cm) collected from each zone, with 3 replicates being analysed in each case. We compared the composition and abundance of the assemblages in the 3 zones to: 1) complement existing knowledge of CCZ foraminifera, including monothalamids; and 2) establish whether the assemblages still reflected impact effects after 20 years. We identified 371 morphotypes and formally recognised species among the Rose-Bengal-stained foraminifera, with assemblages being dominated by monothalamids, a poorly-known group of large foraminifera that is abundant at abyssal depths. Although the similarity of the assemblages was low, the zones did not differ significantly in terms of foraminiferal taxon richness, dominance, or abundance. We conclude that: 1) the foraminifera in the >250 µm class, although typical of abyssal faunas, still represent a fraction of the under-sampled deep-sea macrofaunal foraminiferal diversity; 2) the signature of the disturbance was not evident in these foraminiferal assemblages, either because they had recovered from the disturbance after 20 years or because 3 sample replicates were insufficient to detect differences. The RV SONNE cruise SO 239 was a part of the JPIO Pilot Action project “Ecological Aspects of Deep-Sea Mining”. The research was supported by the Polish National Science Centre grant No. UMO-2014/13/B/ST10/02996.

Nuria Sánchez, Universidad Complutense de Madrid; Lucie Pastor, Ifremer Centre de Bretagne; Lenaick Menot, Ifremer Centre de Bretagne; Daniela Zeppilli, Ifremer Centre de Bretagne

The risk assessment of seafloor massive sulfide (SMS) mining on meiobenthic organisms, specifically on soft-sediment meiofauna, is impeded by a lack of knowledge on the biology and ecology of these communities. In this study, we investigated sediment samples taken in proximity of active vents at Trans-Atlantic Geotraverse (TAG) and Snake Pit, two hydrothermal vent fields of the Mid-Atlantic Ridge, in order to explore metazoan meiofauna, particularly nematode community, and its relation to organic carbon, total nitrogen, total sulfur, and dissolved oxygen. Organic carbon and nitrogen contents were low at both sites. High concentrations of total sulfur and low oxygen penetration were found at Snake Pit compared to TAG. Snake Pit showed approximately four times higher meiofauna and nematode density compared to TAG, as well as a dissimilar nematode community composition. We hypothesize that high sulfur concentrations at Snake Pit may support high microbial growth, which represents one of the main food source for nematodes. Moreover, TAG nematode community mostly consisted of persisters (K-strategists), whereas Snake Pit one was composed by both persisters (Desmoscolecidae family) and colonizers (r-strategists Metalinhomoeus and Halomonhystera), whose presence can be facilitated by the bioturbation effect of polychaetes observed on the sediment surface. Therefore, food availability, geochemical settings, and biotic interactions seem to drive the local meiofauna and nematode community. Our study also draws attention to the opportunity of including meiofauna and specifically nematodes in impact studies conducted in this area in order to assess and monitor the impact of SMS mining.

Sadie Mills, National Institute of Water & Atmospheric Research; Diana MacPherson, National Institute of Water & Atmospheric Research

Like most taxa, zoantharians in the deep sea remain largely unexplored and characterized. Our current knowledge on deep sea zoantharians comes from the deep-sea expeditions of the last centuries and is based on methods and character selection that vary between authors. This led to numerous poorly described local species and some that have never been observed since their original description. Here we will present the result of the examination of over 400 specimens from the South West Pacific and Southern Ocean preserved in the collections of NIWA, New Zealand. Most of these zoantharians were found associated with other organisms and were often collected in economically or ecologically important areas. Whenever possible DNA was obtained from the specimens and the results presented here combine morphological and molecular observations, and distributions compared with historical literature. Our findings reveal an unexpected diversity in the South Pacific deep sea, including potential new genera and the southernmost record of a zoantharian. These findings will be discussed in both biogeographic and evolutionary perspectives.

Magdalena N. Georgieva, Natural History Museum, London, UK; Jonathan T. Copley, University of Southampton; Crispin T Little, University of Leeds, Leeds, UK; Sabine Gollner, Royal Netherlands Institute for Sea Research; Eva Paulus, Royal Netherlands Institute for Sea Research; Adrian G. Glover, Natural History Museum, London, UK

Deep-sea hydrothermal vents exhibit zonation of specialist fauna characterised by proximity to reduced chemical and mineral-rich fluid emission zones. While rarer, hydrothermal vents also exist within shallow marine environments and though easier to reach, relatively few studies exist at these chimneys. Strýtan, located in Eyjafjörður, northern Iceland, is a 45 m tall, shallow-water hydrothermal vent comprised of saponite, with a depth range of 15-60 m. The main chimney shows demarcated seepage zones of white calcium-rich saponite interspersed by dense mats of Arctic sub-tidal marine fauna such as hydroids, bryozoans, echinoderms and mussels, whose interactions with hydrothermal fluids and zonation along the chimney are largely unknown. Assessing their distributions can provide insights into the relative tolerances of Arctic shallow-water marine invertebrates to changing temperature (6-72ºC) and geochemical regimes, the potential for chemosynthetic symbioses at shallow vents, and adaptation of taxa to hydrothermal environments relevant to processes at deep-sea vents. We aim to characterise the zonation of Strýtan, hypothesising that faunal zonation correlates with depth and distance from fluid emission. During June 2019, we conducted SCUBA and ROV surveys of the Strýtan chimney. Screengrabs of footage taken during ROV set-down periods were used in conjunction with DNA barcoding of a subset of collected specimens to identify fauna to the lowest taxonomic level possible and to assess zonation patterns of dominant taxa. Preliminary observations show that fresh saponite deposits in the top 5m of the chimney and in active seepage zones throughout the height of the chimney appear uncolonised, by either algae or further layers of fauna, demonstrating recent deposition. This suggests that a further temporal element may act as a control on colonisation.

Christina Pomee, Tonga Offshore Mining; Akesa Ahokava, Tonga Offshore Mining; Jeffrey C. Drazen, University of Hawaii; Astrid B. Leitner, Monterey Bay Aquarium Research Institute; Adrian Flynn, Fathom Pacific; John Parianos, Nautilus Minerals; Daniel O.B. Jones, National Oceanography Centre

The largest known deposits of polymetallic nodules and relatively high benthic biodiversity occur on the abyssal seafloor of the Clarion Clipperton Zone (CCZ), central Pacific. The environmental factors that regulate faunal communities associated with nodule fields in the CCZ, both at regional and local scales, are not well understood. In this study, seabed image surveys were used to assess regional (hundreds of km) and local (tens of km) distribution patterns in invertebrate and fish megafauna (> 1cm) in relation to key environmental factors: modelled nutrient fluxes to the seabed varying at the regional scale, seabed geomorphological variations varying at the broad local scale (tens of km), and seabed nodule cover varying at the fine local scale (tens of meters). Our results showed that modelled nutrient flux data are a rather poor predictor of regional megabenthic variations, but depth appeared to correlate with faunal abundance. In contrast, geomorphology and particularly nodule cover appeared to exert strong control on faunal abundance and community composition, but not overall species richness. Local variations in abundance and beta-diversity, particularly those driven by nodule presence (within study areas), were of comparable magnitude to those observed at a regional level (between study areas). However, regional comparisons of megabenthic assemblages showed clear shifts in dominance between taxonomic groups across the mid-eastern CCZ seabed, suggesting a potentially higher regional habitat heterogeneity than was previously thought.

Ronnie Glud, University of Southern Denmark; Frank Wenzhofer, Alfred Wegener Institute; Daniel Leduc, National Institute of Water and Atmospheric Research; Daniela Zeppilli, IFREMER

Hadal regions are the deepest areas of the ocean (>6,000m depth). Particulate organic matter (POM) derived from the primary surface production is the main food supply for the hadal zone, although carrion falls and localized chemosynthetic production also provide resources for some hadal communities. Recent investigations of hadal environments have shown that the steep topography of trenches lead to a POM funneling effect resulting in high infauna abundance relative to the adjacent abyssal plain, however several trenches remain poorly sampled. The Atacama Trench is the most southern and deepest trench of the East Pacific Ocean with an extraordinarily high density and biomass of meiofauna in comparison to other trenches and the adjacent bathyal region, which led to the “meiofauna hotspot hypothesis”. Here, we investigate the spatial variability of meiofauna in the Atacama Trench along the trench axis and abyssal and bathyal regions of trench edges. The highest density and biomass were found in the deepest zone of the trench axis, but was not significantly different from abyssal and bathyal sites along the trench edge on the coastline side. Otherwise meiofauna density was lowest on the abyssal site on the trench edge opposite to the coastline and in the southern area of the trench axis. The meiofauna density on the Atacama Trench axis was similar to densities found in South-Sandwich, Tonga and Kuril-Kamchatka trenches but eight times lower than the previous study on the region. Interestingly the quality of organic matter (C:N ratio and chlorophyll-a and phaeopigments) was not correlated with meiofauna density and biomass as previously expected. Even though trenches can be a depocenter of organic matter providing more food for the benthic compartment explaining the higher density and biomass of meiofauna this seems to not be the case in our study.

Chih-Lin Wei, National Taiwan University; Mauricio Silva, Florida State University; Amy Baco, Florida State University

Major depressions in the northern Gulf of Mexico (GOM) are centers of organic matter accumulation and biodiversity, but fine-scale spatial patterns and environmental drivers have not been characterized. A project studying the impact of the Deepwater Horizon (DwH) oil spill allowed for the sampling of macrofauna within the DeSoto Canyon along the canyon wall and axis, and adjacent slope, as well as potential drivers of community structure among sediment, terrain, and water mass parameters. Canyon abundance decreased, evenness increased, and family richness followed the expected parabolic curve with depth. Cluster analysis identified three depth-related groups within the canyon that conformed to established bathymetric boundaries for the GOM non-canyon slope: stations at < 500 m clustered into Group I, 669 – 1834 m into Group II, and > 2000 m into Group III. Canyon community structure strongly correlated with fluorescence and oxygen concentration, combined with any of salinity, particulate organic carbon (POC), sediment organic carbon, or slope. Across the habitats of canyon axis, wall and non-canyon slope, abundances were highest on the canyon wall. Community structure differed between habitats and most strongly associated with oxygen and POC. Community differences between the canyon wall and axis may result from microhabitat heterogeneity resulting from potential hydrocarbon seepage, organically-enriched sediment deposits along channels, or remnant influence from the DwH. Even at the current study’s resolution, faunal patterns could not be fully explained by available abiotic factors, emphasizing the need for greater sampling resolution when delineating the spatial processes in dynamic environments such as marine canyons.

Taylor Heyl, Woods Hole Oceanographic Institution; Luke McCartin, Lehigh University; Elisabeth McElwee, Duke University; Steve Auscavitch, Temple University; Erik Cordes, Temple Unversity; Randi Rotjan, Boston University

Deep-sea corals provide habitat for a diverse array of symbiotic species. To date, more than 3500 species from 5 phyla: Cnidaria, Annelida, Mollusca, Arthropoda and Echinodermata occur as symbionts with deep-water corals. Several studies have shown specific relationships between corals and associated symbionts, however, little is known about the regional composition, diversity, distribution, ecological requirements, and the strategies that maintain relationships among coral species and symbionts. In March and October 2017, we conducted the first deep-water biological surveys within the largest and deepest UNESCO World Heritage Site on Earth, the Phoenix Islands Protected Area. We investigated the symbiotic partnerships among cold-water corals and their associated fauna: their composition, distribution, functional diversity, and apparent degree of host specificity. More than 77 coral collections with symbiotic epifauna were obtained and more than 75 coral-associated fauna were genetically barcoded. Multi-gene barcodes and genealogies of symbiotic fauna, including ophiuroids, munid and chirostylid crabs, gastropods, and egg masses reveal a higher than anticipated phylogenetic diversity of symbionts and a greater amount of host-associate specificity. In addition, the number of coral-associated epifaunal species decreased with depth, while the specificity of paired relationships increased with depth. These data combine to form a baseline of deep-sea coral ecosystem diversity and biogeography along with frequency and specificity of coral-associated communities critical to evaluating the future impact of changing oceanographic conditions, host/habitat availability, and of marine protected areas on deep-sea ecosystems.

Breea Govenor, Rhode Island College; Costantino Vetriani, Rutgers University; Charles O'Brien, Rutgers University; George Luther, University of Delaware; Richard Lutz, Rutgers University

Both the chemical composition of hydrothermal vent fluids and microbial biofilms are proposed as factors that facilitate or inhibit the settlement and colonization by fauna. We conducted time-series in -situ experiments (6 week and 6 month durations at two sites) using artificial substrates, TAMS (Temporal Autonomous Multi-disciplinary Substrates) to examine co-located linkages between hydrothermal fluid chemistry (in-situ measurements of H2, H2S, pH and temperature), and microbial and metazoan colonization amongst newly-formed post-eruptive vents. We: 1) characterized the composition of microbial and metazoan colonizers; 2) investigated physiological and functional attributes of microbial colonizers; 3) correlated relationships between microbial and macrofaunal colonization to relationships between fluid chemistry, pH, temperature; and 4) related these results to the observed changes in hydrothermal fluid flux and biological community structure. While chemical, microbial and metazoan colonists differed significantly at the different sites, strong correlations were observed among average temperature, sulfide, and the relative microbial abundance of Leucothrix sp. and Methylococceae, Sulfurovum lithotrophicum, Sulfurovum sp., Cytophaga sp., and Desulfocapsa sulfexigens. Similarities in the composition of macrofaunal colonists were highly correlated with average temperature, median sulfide and median oxygen concentrations. For example, Tevnia jerichonana colonized all TAMS in diffuse flow > 18°C (with maximum H2S concentrations as high as 103.7 μM) and did not colonize TAMS with maximum temperatures < 5°C. There were strong correlations among specific microbial groups and the abundance of macrofaunal species. Through these integrated studies, we identified marked differences in short-term microbial community development, in-situ fluid chemistry, and vent-endemic metazoan colonization that suggest causal relationships among them.

Miodeli Nogueira Jr., Universidade Federal da Paraiba; Dhugal Lindsay, Japan Agency for Marine-Earth Science and Technology (JAMSTEC); Greg Rouse, Scripps Institution of Oceanography

The unusual holopelagic annelid Poeobius meseres Heath, 1930 (Flabelligeridae) was originally described from Monterey Bay, California, and has been subsequently recorded across the northern Pacific from Japan to the Gulf of California. Rare occurrences in the eastern tropical Pacific, as far as 7° S off Peru, have been questioned as possibly comprising a separate species. Using molecular phylogenetic analysis of a newly collected specimen from the Salas y Gomez Ridge (25.4° S, 81.8° W), 1100 km off Chile, we extend the known geographic range of P. meseres southward by 2040 km. This subtropical specimen showed higher genetic similarity to a specimen from the type locality (1.48% corrected pairwise COI distance) than to representatives from the Aleutian Islands (5.28%) and Japan (6.44%), confirming the presence of P. meseres sensu stricto in the southeastern Pacific. The extended range of P. meseres now encompasses the sole collection locality, off Ecuador, of Enigma terwielii Betrem, 1925, a pelagic annelid with purported morphological similarities to P. meseres but considered a nomen dubium due to the loss of its type material. We therefore suggest that the sole record of E. terwielii was most likely an occurrence of P. meseres. The biogeographic implications of our single P. meseres specimen, captured serendipitously in a passive vertical net affixed to a towed camera system, highlight the importance of deep submergence technologies and fundamental biodiversity exploration.

Ashley Rowden, NIWA/ Victoria University Wellington; Andrew Thurber, Oregon State University; Cliff Law, NIWA/University of Otago ; David Bowden, NIWA; Kathy Campbell, University of Auckland; Lisa Levin, Scripps Institution of Oceanography; Lucy Stewart, Toha Foundry Ltd.; Olivia Pereira, Scripps Institution of Oceanography

As global interest in commercial extraction of methane from gas hydrates intensifies there is an urgent need to understand what implications this may have for surrounding ecosystems. The Hikurangi Margin offshore of Aotearoa New Zealand is an area with both the geologic potential for hydrate mining and economic interest in such activity. HYDEE (Gas Hydrates: Economic Opportunities and Environmental Implications) is a multi-disciplinary research programme designed to address a number of questions, including: Would hydrocarbon production from gas hydrates significantly impact seafloor stability, ecological processes, and ocean biogeochemistry? Through a series of multidisciplinary cruises, this programme has employed an integrated biological and biogeochemical approach to advance our understanding of how hydrate mining may impact the biological diversity and ecosystem services of New Zealand. The overall aim of the program is creating a data-informed environmental risk assessment for energy production from hydrate resources. This assessment, inclusive of geologic and geophysical aspects of HYDEE, will determine the socio-economic implications of gas hydrate production in New Zealand and result in a framework that can be applied in other regions of potential hydrate resource extraction.

Warren R. Francis, University of Southern Denmark; Jakob D. McBroome, Department of Biomolecular Engineering and Bioinformatics, University of California Santa Cruz; Lynne M. Christianson, MBARI; Steven H.D. Haddock, MBARI and UC Santa Cruz; Richard E. Green, Department of Biomolecular Engineering and Bioinformatics, University of California Santa Cruz

We know little about the features of chromosome architecture and evolution that apply to all metazoans. Ctenophores, or comb jellies, are arguably the sister phylum to the rest of the metazoa, and therefore share a multicellular ancestor with all other animals. Previous studies of fragmented genome assemblies in comb jellies helped characterize the protein evolution unique to animals. However, until recently it was technically infeasible to reconstruct chromosome-scale genome assemblies. Here, we present a chromosome-scale, fully-phased genome assembly of the ctenophore Hormiphora californensis, and another genome assembly of the ctenophore Beroe forskalii. Comparisons to other genomes reveal that many elements of chromosome structure and organization predate the bilaterian animals, and define several ‘rules of life’ for animal genome structure and evolution.

Tracey T. Sutton, Nova Southeastern University; Dr. Rosanna J. Milligan, Nova Southeastern University

The Deepwater Horizon Oil Spill in 2010 dramatically increased the need for research of the deep sea after 205.8 million gallons of oil were spilled to the northern Gulf of Mexico, 1544 meters below the surface. One important ecological tool for more rapid monitoring and management implementation is a biological inventory for analysis of patterns in vertical migrations, assemblage structures, life stage habitats, and a roster of inhabitants to better prepare for the next deep-sea spill. Biological inventories provide key information to help fill in the knowledge gaps, but there needs to be a balance between taxonomic detail, speed, and quality of identification. Considerable expertise is required to classify faunal specimens to genus and species, which may not be readily available to resource managers working in the relatively poorly studied deep ocean environments following an impact. This study will analyze biodiversity and assemblage structure patterns from samples collected with a large, commercial-sized, high-speed rope trawl between November 2010 and September 2011. Trawls were conducted primarily between 0-797 m depth (“shallow”) and 0-1800 m depths (“deep”), night and day at each station. Of 88 high-speed rope net deployments, 190,442 pelagic fishes were collected and identified. This large collection of deep pelagic fishes will be used, as collected through the Offshore Nekton Sampling and Analysis Program, to conduct a quantitative analysis of the pelagic fish assemblage and analyze the community structure across the two depth categories with respect to diel cycle and survey month. Taxonomic resolution across trawl samples will be analyzed and compared to determine the level of classification that would statistically best suit in-field identifications for future management purposes while maintaining adequate information for ecological statistics. Study results will be discussed in the context of offshore monitoring and management for the Gulf of Mexico.

Fanny L. González-Zapata, University of Los Andes; Luisa F. Dueñas, Departamento de Biología, Universidad Nacional de Colombia

Gorgonian corals imprint a unique seascape in the shallow-water communities of the Western Atlantic reefs and adjacent seas, including Mesophotic Coral Communities (MCEs). It is unknown if gorgonians at MCEs are the extension of shallow or deep-sea communities or whether mesophotic octocorals comprised different evolutionary lineages. Using a time-calibrated molecular phylogeny (mtDNA: mtMutS), we examined the lineage membership of mesophotic gorgonians in comparison to shallow and deep-sea lineages of the wider Caribbean-Gulf of Mexico and the Tropical Eastern Pacific. Our results show MCE gorgonians rising mostly from old octocoral lineages closely related to deep-sea species, whereas shallow-water species comprise younger lineages. The mesophotic gorgonian fauna in the studied areas are rarely related to their zooxanthellate shallow counterparts, and thus cannot serve as a refuge or as a source of propagules. In American waters, only Muricea (Plexauridae) comprise a remarkable aposymbiotic group; all Eastern Pacific species, and the mesophotic Gulf of Mexico Muricea pendula, lack algae symbionts whereas all shallow-water Caribbean species engage in symbiosis with Symbiodinaceae. Still, in the Caribbean there are two families, which most species distribute within the MCE range: Keroeididae and Ellisellidae. The latter family comprise a major component of the mesophotic gorgonian coral assemblage, attaining high densities in the upper MCE range and the only lineage where MCEs promoted a clear radiation not seen in any other octocoral group.

Lorena Neira, Universidad de Los Andes, Bogotá DC; Andrea Quattrini, Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution; Juan Armando Sanchez, Universidad de Los Andes, Bogotá DC

Deep-sea exploration is without doubt one of the most challenging-to-perform activities on Earth. It faces technological and natural restraints and it strongly relies on technological developments. That is also the case for the Deep-sea education reach but a drawback that could be used to foster an innovative classroom environment. We introduce a ‘Deep-Sea Exploration’ graduate-level course with a foundation in active and virtual learning. Because virtual education is setting the pace in current times, here, we share the outline of this course with specific activities that can be used to engage students in classrooms across the world. Students are expected to take three roles: researcher, entrepreneur, and explorer to account for the intrinsic relationship between deep-sea scientists and other career practitioners. All roles prioritize collaborative work among students and motivate them to be creative, autonomous, and innovative. The course methodology exposes students to the deep-sea community through challenges such as grant proposal writing (Researcher), business idea innovation tanks (Entrepreneur), and novel discovery annotations on deep-sea exploration cruises lived stream via telepresence (Explorer). More than receiving information provided solely by lectures and readings, students in ‘Deep-Sea Exploration’ use tools to build on their knowledge and to spot real-world opportunities for professional growth.

In recent years, the evolutionary relationships within the rhizarian clade Foraminifera have been revealed by numerous molecular phylogenetic studies. With the publication (June 2020) of the PhyloCode, a rank-free system of biological nomenclature, the opportunity exists for formally naming some of the major subclades of Foraminifera following the rules of phylogenetic nomenclature. Phylogenetic nomenclature, an alternative to the rank-based Linnean system, names clades of organisms with explicit reference to published phylogenetic trees. Xenophyophores are a clade of deep-sea agglutinated foraminiferans that branch within the more inclusive unnamed “Clade C” as the probable sister group to saccaminids, and may represent the earliest branching multi-chambered foraminiferans, or alternatively, an independent experiment in multilocularity. This presentation introduces the basics of phylogenetic nomenclature and reviews the various challenges involved in writing a phylogenetic definition for Xenophyophora Schulze, 1904. Some of the questions that I will attempt to answer are: (1) Which type of definition is most appropriate for the clade (i.e., minimum-clade definition, maximum-clade definition, or apomorphy-based definition)? (2) Which species could be used as internal and/or external specifiers? (3) Which published phylogeny should be chosen as the reference phylogeny for Xenophyophora? (4) And, what are the diagnostic apomorphies for the clade?

Furu Mienis, NIOZ Royal Netherlands Institute for Sea Research and Utrecht University; Jay Lunden, Temple University; Jennifer Miksis-Olds, University of New Hampshire; Dylan Wilford, University of New Hampshire; Andrew J. Davies, University of Rhode Island

Passive acoustic monitoring can be used to characterize ocean soundscapes by monitoring the frequencies and levels of sound over time and space. Through co-located sensor and video observations and an understanding of the sounds, the sources contributing to the acoustic environment field can be identified and grouped into biological sounds (e.g. animal feeding, behavior) or environmental sounds (e.g. waves, currents). In this study we aimed to characterize the local soundscape of a deep-sea coral community, with an objective to improve understanding of the physical and ecological processes occurring within these enigmatic habitats. Hydrophones were mounted to ALBEX landers and passively recorded acoustic data, in addition to abiotic variables including temperature, dissolved oxygen, current speed/direction, backscatter, turbidity, and fluorescence from lander-mounted sensors. A baited video camera system offering bait at pre-programmed intervals was attached to the lander frame to study the temporal variation in presence of scavenging fish and invertebrates. Two lander deployments were conducted, AB1 and AB2, and were both deployed in April 2019 at Richardson Reef Complex, a cold-water coral reef in the Southeastern US, (77° 21.168 N, 31° 53.922 W). AB1 collected 3 days of data and AB2 collected data for 3 months. Potential local transient sounds were identified by analyzing sound level peaks above the daily 95th percentile in high frequency, broadband (10-64 kHz, Broadband) recordings. Peaks in the acoustics were aligned with co-occurring video data and environmental conditions to assign the sound source as either biological or environmental in nature. The duration and magnitude of significant changes in environmental parameters were also noted, showing extreme variations in temperature and dissolved oxygen. These events, related to the meandering of the Gulf Stream last for 46 hours and are significant as they may be potential stressors to the reef habitat.

Telmo Morato, OKEANOS-IMAR/University of Azores; Carlos Dominguez-Carrió, OKEANOS-IMAR/University of Azores; Lene Buhl-Mortensen, Institute of Marine Research/Norway; Pal Mortensen, Institute of Marine Research/Norway; Christopher Pham, OKEANOS-IMAR/University of Azores; Henrique Cabral, MARE/University of Lisbon; Marina Carreiro-Silva, OKEANOS-IMAR/University of Azores

The Atlantis-Meteor Seamount Complex (AMSC) is an isolated group of open-ocean guyots in the Portuguese extended continental shelf. Here, we present the results of a study carried out on the western flanks of two poorly studied seamounts from the northern and central part of the complex: the Atlantis and Irving. The characterisation of the megafauna communities was based on eight video transects conducted by a Remotely Operated Vehicle (ROV) between 300 and 2600 m depth. Abundance of megabenthic organisms was generally low reflecting the low productivity of the area. However highly heterogenous habitats hosted dense patches of habitat-forming species (e.g. octocoral Viminella flagellum and lithistids sponges). Seven epibenthic communities were identified, whose distribution was markedly explained by depth and the availability of soft and hard substrates. The upper and lower summits (200-700 m) were characterized by a mixture of Atlanto-Mediterranean and NE Atlantic species but also by Trans-Atlantic species, possibly determined by the confluence of the Northeast Atlantic Central Water of the Azores current branch at the Atlantis and the Subtropical Mode Water at Irving. In flank areas, at depths of 700-1500 m (upper to mid bathyal), where intermediate water masses predominate (Mediterranean Outflow Water and the modified Antarctic Intermediate Water), three different communities with distinct sponge fauna and sparse solitary corals were depicted. The proportion of species with a wide distribution typical of bathyal open-ocean zones was three times higher than NE Atlantic species due to a widely distributed hexactinellid fauna. Biogeographically restricted species (e.g. Poliopogon amadou) and new records (e.g. Iridogorgia fontinalis) were also observed. AMSC may represent an Ecologically and Biologically Significant Areas (EBSA) based on its isolation and remoteness, uniqueness and vulnerability in parallel with the low productivity and naturalness of the region.

Antonio Godinho, Okeanos Research Unit of the University of the Azores; IMAR-Marine Institute; Meri Bilan, University of Salento; Covadonga Orejas, Instituto Español de Oceanografia; Marina Carreiro-Silva, Okeanos Research Unit of the University of the Azores; IMAR-Institute

Cold-water octocorals are important habitat-forming species in the deep sea, harboring rich biodiversity. Their key ecological role and high vulnerability to human impacts have resulted in their classification as priority species for conservation. Although there are increasing efforts to unravel the reproductive biology of deep-sea octocorals, information on their early life history stages is still scarce, limited to few species. The present study aims to describe the larval biology of two common octocoral species in the Azores Archipelago, Viminella flagellum and Dentomuricea aff. meteor. Both species are common in local seamounts between 150 and 600 meters, where they often form mixed coral gardens. However, V. flagellum has a widespread distribution outside the Azores, while D. meteor is a regionally endemic species. Larvae of both species were reared in aquaria and observed to describe their embryonic development and determine their larval characteristics, such as buoyancy, swimming behavior, Pelagic Larval Duration (PLD) and settlement behavior. The results are compiled to make hypothesis on the dispersal capacity of the two species and are discussed in conjunction with other life history traits, such as reproduction and resource acquisition. This approach can contribute to a more holistic understanding of deep-sea corals and the communities their form.

Frédéric Planchon, University of Brest / Ifremer; Brian P.V. Hunt, Institute for the Oceans and Fisheries, University of British Coumbia; Boris Espinasse, UiT The Arctic University of Norway, Tromsø, Norway; Evgeny Pakhomov, University of British Coumbia; Fabienne Le Grand, Philippe Soudant, University of Brest / Ifremer

Knowledge of the trophic ecology of zooplankton is essential for evaluating their functional roles in food webs and nutrient cycling since they represent the link between primary producers and higher trophic levels. Sub-Antarctic islands are areas of high productivity due to input of the essential micronutrient Fe associated with the island mass effect, which promotes phytoplankton blooms mostly characterized by diatoms, haptophytes and dinoflagellates. These groups are known to produce long-chain polyunsaturated fatty acids (PUFA), essential components for organismal function, and consumers, such as zooplankton, must acquire them through their diet. Here we used lipids and fatty acid analyses to investigate the trophic composition of zooplankton in the vicinity of the Sub-Antarctic Kerguelen Islands, in areas that experience contrasting high and low phytoplankton productivity conditions. Samples were collected in late austral summer 2018 as part of the MOBYDICK research project. Preliminary analyses confirmed the presence of a phytoplankton bloom at high productivity stations, and identified signals of diatoms, haptophytes and dinoflagellate fatty acid trophic markers. Zooplankton lipid composition was characterized by a high proportion of triglyceride, with no clear differences among stations. Ultimately, the results of this work will provide information on the importance of zooplankton to energy flow and carbon flux in the Southern Ocean.

Rosanna Milligan, Nova Southeastern University; Tracey Sutton, Nova Southeastern University

Tunas are ecologically important in pelagic ecosystems as they are top predators that connect the epi- and mesopelagic zones through deep dives and preying on migrating fishes. However, due to their high economic value, most species are overfished. Declines in fishery landings of large-bodied tuna species in the Gulf of Mexico (GoM) are expected to drive increased fishing pressures on unmanaged, understudied, small-bodied tuna species. While predicting spawning stocks and recruitment success focuses on estimates of larval abundances, juveniles may provide a better estimate of future adult stock sizes, as they are more likely to survive to adulthood. However, distributional studies on juveniles are rare, leading to a gap in our understanding of tuna ecology. In the present study, tuna early life stages were collected across the GoM from December 2010-September 2011 (Offshore Nekton Sampling and Analysis Program) and in May and August from 2015-2017 (DEEPEND Consortium). The size class examined in this study, representing large larvae and small juveniles, is larger than that of previous larval tuna studies in the GoM. In total, 11 of the 16 scombrid species inhabiting the GoM were collected, with small-bodied tuna species (Euthynnus alletteratus and Thunnus atlanticus) dominating the assemblage. Generalized additive models indicated that juvenile E. alletteratus were associated with productive continental shelf/slope environments (low salinity, high chlorophyll a concentrations, nearer to shelf break), while T. atlanticus juveniles were associated with oligotrophic habitats (high salinity, low chlorophyll a concentrations, further from shelf break). These results demonstrate that over a broad spatiotemporal domain, large larvae and juvenile tunas partition pelagic habitat on the mesoscale in addition to the temporal partitioning of adult spawning. These factors are important for spatially and temporally explicit modeling aimed at predicting tuna stock sizes.

Maiara Monteiro Oliveira, Pontifical Catholic University of Rio Grande do Sul; Renata Medina-Silva, Pontifical Catholic University of Rio Grande do Sul

Over half the total organic carbon on Earth’s surface is trapped in marine sediment as methane hydrates. These crystalline structures of water and gas molecules remain stable in sediment zones of low temperature and high pressure, seeping to the water column upon dissociation. The detection of seafloor pockmarks produced by gas seeps has led to the identification of a methane hydrate province in the South Atlantic Ocean, the Rio Grande Cone (RGC). Over the years, we have strived to characterize this reservoir and the microbial life therein. Our results suggest that the methane stored in the RGC, which may account to 22 trillion m3, has biogenic origin and fuels complex chemosynthetic communities. Through diverse approaches of metabarcoding, culturing, and biochemical assays, we have identified anaerobic methanotrophic (ANME) archaeal groups and isolated methane-oxidizing bacteria with broad metabolic potential. From sediment harboring Vestimentifera tubeworm clusters, we cultured strains of Brevibacillus sp., Paenibacillus sp. and four taxonomic groups of the genus Bacillus. Through dilution-to-extinction and exposure to methane as sole carbon source, we isolated strains of the Pseudomonas fluorescens complex from sites containing gas hydrates. Among these fluorescent siderophore-producing strains, whole genome sequencing of the most taxonomically distinct isolate suggested a robust methylotrophic pathway, with C1 assimilation through the serine cycle. Moreover, this strain encoded ammonia monooxygenase (AMO) characteristic of heterotrophic nitrifiers. AMO shares the ability of methane oxidation with aerobic methanotrophy enzymes, which could have allowed our isolate to grow on methane. Our results comprise the characterization of a novel methane cold-seep region in the South Atlantic Ocean, providing phylogenetic and genomic insights on the microbial communities from the RGC.

Rhoderick Burgass, Heriot-Watt University; Manolis Mandalakis, "2.; Hellenic Centre for Marine Research" Apostolos, Spyros; University of Crete Petros, Gikas; Technical University of Crete Finlay, Burns; Marine Laboratory, Aberdeen Jim, Drewery; Marine Laboratory, Aberdeen

Whereas upper ocean pelagic sharks are negatively buoyant and must swim continuously to generate lift from their fins, deep-sea sharks float or swim slowly buoyed up by large volumes of low-density oils in their livers. Investigation of the Pressure, Volume, Temperature (PVT) relationships for liver oils of 10 species of deep-sea Chondrichthyes shows that the density difference between oil and seawater, Δρ remains almost constant with pressure down to full ocean depth (11 km, 1100 bar); theoretically providing buoyancy far beyond the maximum depth of occurrence (3700 m) of sharks. However, Δρ, does change significantly with temperature and we show that the combined effects of pressure and temperature can decrease buoyancy of oil by up to 10% between the surface and 3500 m depth across interfaces between warm southern and cold polar waters in the Rockall Trough in the NE Atlantic. This increases drag more than 10 fold compared with neutral buoyancy during horizontal slow swimming (0.1 m s-1) but the effect becomes negligible at high speeds. Chondrichthyes generally experience positive buoyancy change during ascent and negative buoyancy change during descent but contrary effects can occur at interfaces between waters of different densities. During normal vertical migrations buoyancy changes are small, increasing slow-speed drag by no more than 2-3 fold

Alicia Veuillot, Université du Littoral Côte d'Opale; Marjolaine Matabos, IFREMER; Eric Thiebaut, Station biologique de Roscoff - Sorbonne

While we are starting to have a better understanding of recolonization and connectivity processes along continuous mid-oceanic ridges, less is known about back-arc basins of the western Pacific. Furthermore, hydrothermal vents which form unstable and fragmented habitats are increasingly becoming the target of deep sea mining societies. Understanding populations resilience to natural and anthropogenics disturbance requires a better knowledge of species life history traits. To this aim, we examined the reproductive biology and recruitment processes of the hydrothermal vent limpet, Lepetodrilus schrolli in relation to different habitats and environments. Samples were collected in Bathymodiolus sp. and Ifremeria nautilei habitats at several vent sites in the Manus Back-arc Basin during the CHUBACARC cruise in 2019. Population structure, gonad morphology, gametogenesis and fecundity were analysed using individuals size frequency distributions and histological analyses. An unequal sex-ratio, with almost 80% of female among 159 individuals was observed. As the others Lepetodrilidae, L. schrolli is gonochoric and seemed to have continuous or quasi-continuous gametogenesis and asynchronous reproduction among individuals; all stages of oocyte development were present in the gonad with a maximum oocyte size of 188 µm. Fecundity varied between 33 and 115 with a mean of 64 matured oocytes per female. These results suggested a lecithotrophic development of the larvae. Size-frequency distributions were consistent with a continuous recruitment although episodic larval supply could blur the signal. According to our observations neither population structure nor reproductive biology seemed to be influenced by the habitat, whereas biotic and environmental processes could have an effect on gametogenesis, growth and mortality.

Bernard Angers, Université de Montréal; Robert Young, NOC; Kim Juniper, University of Victoria

Many foundation species in chemosynthetic-based environments rely on their environmentally acquired symbiotic bacteria for their survival. Hence, understanding the biogeographic distributions of these symbionts at the regional scale is key to understanding patterns of connectivity and predicting resilience of their host populations (and thus whole communities). However, such assessment is challenging because it necessitates to measure bacterial genetic diversity with an incredibly high resolution. For this purpose, the recently discovered Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) constitute a promising new genetic marker. These DNA sequences harbored by about half of bacteria hold their viral immune memory and as such, may allow for discriminating different lineages or strains of otherwise indistinguishable bacteria. In this study, we used high-throughput CRISPR-typing to characterize the regional population structure of the obligate symbiont species Candidatus Endoriftia persephone on the Juan de Fuca ridge. Mixed symbiont populations of Ca. Endoriftia persephone were sampled across individual R.piscesae hosts from contrasting habitats in order to determine if environmental conditions rather than patterns of connectivity are more important drivers of symbiont diversity. Finally we assessed the potential of CRISPR as a hypervariable phylogenetic marker by comparing the CRISPR-based population structure to that uncovered from the more traditionally used approach of Multi-Locus Sequence analysis (MLSA). This research is a step towards making keystone microbial specie an integral part of conservation policies for upcoming mining operations.

Brenda L. Doti; Daniel Roccatagliata, Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA, CONICET/UBA) & Departamento de Biodiversidad y Biología Experimental (DBBE, FCEN/UBA)

The taxonomy of the genus Pseudione remains unresolved. At present, a heterogeneous assemblage of species, not congeneric with the type species of the genus Pseudione, is provisionally named “Pseudione sensu lato”. A new bopyrid that belongs to this group of species is herein reported. This parasite (an ovigerous female and its accompanied male) was found inside the right branchial chamber of Munida spinosa Henderson, 1885, a squat lobster that distributes along the Argentine Continental slope from off Buenos Aires Province to Malvinas (Falkland) Islands and Burdwood Bank. This infested squat lobster was obtained with a bottom otter trawl in the Mar del Plata submarine canyon (38°01.49’S, 54°44.17’W) at 819 m depth during the “Talud Continental I” survey, carried out by the Argentine RV Puerto Deseado in 2012. This is the first time a bopyrid isopod infesting Munida spinosa has been reported. This parasite has crenulated coxal plates and thus, it seems to belong to the Pseudione “crénelés” group proposed by Bourdon. This group currently contains seven species, all of them infesting anomuran decapods (families Munididae and Munidopsidae). The new parasite herein reported can be separated from the other species of the “crénelés” group by presenting the following combination of characters: (1) frontal lamina narrow and smooth, (2) both sides of the body convex, and (3) tergal projections I-V with irregular margins (more evident on right side). Finally, the taxonomic status of the “crénelés" group is briefly discussed. Key words: Pseudione sp.; Munida spinosa; new species; continental slope; Argentina"

Jennifer Gonzalez, Scripps Institution of Oceanography, UCSD; Guillermo Mendoza, Scripps Institution of Oceanography, UCSD; Connor Coscino, Scripps Insitution of Oceanography; Jorge Cortés, Centro de Investigación en Ciencias del Mar y Limnología, Universidad de Costa Rica; Erik Cordes, Department of Biology, Temple University; Lisa Levin, Scripps Institution of Oceanography, UCSD

Authigenic carbonate rocks generated by methane seepage sustain a dynamic invertebrate assemblage that responds to gradients in seepage and interacts with background communities. To examine the effects of changing seepage activity in time at Mound 12, Pacific margin of Costa Rica, on faunal composition, density, and trophic structure, we compared invertebrates on carbonate rocks (i) sampled at active and transition sites in 2017 versus 2018, and (ii) transplanted to different seepage conditions for 17 months. We observed interannual variability in composition at actives sites (2017 vs 2018), suggestive of a decline in seepage and associated chemosynthetic food sources. For rocks transplanted from actively seeping sites to sites with lesser seepage, many taxa persisted over one year by either adapting their diets or by retaining their symbiotic bacteria and access to methane-derived carbon. In the other direction, the rapid colonization of grazers on carbonates transplanted from transition sites to active sites suggests a rapid establishment of the chemosynthetic bacterial community within 17 months. Additionally, some transition species survived transplantation to active seepage, indicating tolerance of potentially stressful conditions. Overall, the seep and surrounding assemblages exhibit considerable resilience and quick response to temporal variation in seepage. This observation is crucial to predict community responses to natural or anthropogenic disturbance to seepage activity and should be included in management and protection plans.

Katleen Robert, Memorial University, Newfoundland; Alex Callaway, Agri-Food and Biosciences Institute, Belfast; Robert Hall, University of East Anglia, UK; Claudio Lo Iacono, Spanish National Research Council, Barcelona; Veerle Huvenne, National Oceanography Centre, UK

Submarine canyons are complex geomorphological features that incise continental margins and act as conduits between the shelf and deep-sea. Canyons can represent deep-sea biodiversity hotspots, capable of supporting vulnerable marine ecosystems (VMEs). Effective spatial management and conservation of VMEs requires accurate distribution maps and a deeper understanding of the processes that generate the observed distribution patterns. Faunal distributions have been linked to the high spatio-temporal environmental heterogeneity that occurs at varying spatial scales in canyons. Canyons are recognised as sites of intensified hydrodynamic regimes, with internal tides linked to enhanced mixing and nepheloid layer production: processes associated with faunal distributions. Canyon faunal distributions also respond to physical oceanographic (water mass characteristics and hydrodynamics) gradients, which internal tides can generate by their movement along the canyon. Despite evidence of internal tides generating environmental heterogeneity, parameters of internal tide dynamics have rarely been included in studies of canyon fauna. Here we investigate if spatial patterns in internal tide dynamics and associated environmental variability induced by the internal tide, explain variation in spatial patterns of fauna in a deep-sea canyon. We take an interdisciplinary approach utilising biological, oceanographic and bathymetric derived datasets to undertake high-resolution predictive modelling and community analysis of epibenthic assemblages within Whittard Canyon. Results show that spatial variability in depth (and its covariates), seafloor characteristics and internal tide dynamics interact at different scales to determine spatial patterns in epibenthic megafauna. The results further support the role of the internal tide as a structuring force of assemblages and diversity by generating both spatial and temporal gradients in food supply and water mass characteristics.

Marin Schwentner, Natural History Museum Vienna; Saski Brix, DZMB Hamburg

The species Haploniscus bicuspis (Sars 1877) is distributed in the North Atlantic and subarctic waters around Iceland. It was previously divided into subspecies based on male morphology by Wolff (1962). Since, this potential species complex was not resolved and the holotype does not show the essential male characters drawn by Wolff (1962). In this study, we integrate two genetic marker systems: the mitochondrial COI gene and nuclear DNA through ddRAD analyses. Animals were collected during cruises in 2011, 2013 and 2018 in the deep sea around Iceland. Species delimitation was done using ABDG and GMYC with COI data, and principal component analyses and structure analyses were performed to differentiate different groups in ddRAD data. Results show that within the currently identified H. bicuspis, there is a species complex with three putative species found around Iceland. One species is found north, east and southeast of Iceland (with uncorrected p-distances up to 3.82%). This species can be split into different lineages, for instance the COI haplotypes suggest a clear separation between populations directly north of Iceland, east of Iceland and southeast of Iceland. In ddRAD analyses, animals are split into a northern, southern, and deep group, with animals found directly east of Iceland in shallower waters that are potential hybrids. West and directly south of Iceland, two putative species are found that are clearly differentiated in both COI and ddRAD analyses. Asellote isopods including Haploniscus do not possess a pelagic larval stage. They are brooders, suggesting that migration may be limited. The Greenland-Iceland-Faroe Ridge is likely to be the major barrier that hinders gene flow around Iceland, as confirmed through the geographically restricted lineages and putative species found. This study adds valuable baseline information on species delimitation in isopods and biodiversity around Iceland.

Wania Duleba, University of São Paulo

The Antarctic Peninsula (PA) region is essential for ocean circulation and global temperature equilibrium, as well as having large freshwater reservoirs, hydrocarbon and gas hydrate reserves. Benthic organisms from these locations, such as foraminifera, respond rapidly to environmental variations and are widely used in more accurate monitoring studies. In this work, foraminifera associations were analyzed concerning granulometric and geochemical parameters (major and trace elements) of regions rich in gas hydrate, in deep sea of located at AP. For this purpose, surface and subsurface sediments were analyzed from Drake Passage (PD) in two cores (20 cm long) at 3800 m depth. Foraminifera density and diversity values found here are rarely described in the literature for the Antarctic region. The results of foraminifera associations in the PA region are composed of several agglutinant species. Cluster analysis showed associations with different ecological attributes.. In the Drake area, both in bio as well as in thanatocoenosis, there was a dominance of typical species of hypoxic environments and rich in organic matter (e.g., Adercotryma glomeratum and Spiroplectammina biformis). Principal Component Analysis revealed that dissolved oxygen in sediment, granulometry, CaCO3 and trace elements concentrations were the main variables that influenced species distribution. It was not possible to identify changes in organisms and the relation to ecological standards due to gas hydrate. Thus, further studies are necessary, such as morphological and chemical analysis of foraminifera tests, especially in agglutinating species, even more so in regions such as PA, which are known to be more sensitive to climate change and of great importance to the Earth's climate balance.

Michel E. Hendrickx, Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología; Martín Soto-Jiménez, Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología

The northeastern Paciﬁc harbors the world’s largest oxygen minimum zone (OMZ). In the OMZ lower boundary, benthopelagic megafauna aggregates in an organically enriched environment. Yet, the flux and fate of such organic matter (OM) is virtually unknown. Stable isotopes of carbon and nitrogen were used to study the food web structure of the benthopelagic community in the lower boundary of the northeastern Pacific OMZ off western Mexico, at ca. 800 m, where mild hypoxic conditions with oxygen concentration of 0.23±0.01 ml l-1 are found. A total of 44 species (including mysids, polychaetes, cnidarians, echinoderms, mollusks, decapod crustaceans, and fish) were analyzed. The isotopic compositions of primary food sources, including sedimented and suspended OM, giant kelp and seagrasses collected in deep hauls, were also obtained, and their use by megabenthos was evaluated. Besides, the community composition was explored to understand patterns in food use. Mean stable carbon isotopic values of suspended and sedimented OM were lowest among all and fell within the range observed for material derived from phytoplankton. Giant kelp and seagrasses were not important food sources for megabenthos. The 13C of benthopelagic fauna ranged from -20.44‰ (the myctophid Argyropelecus affinis) to -14.09‰ (the benthic gastropod Neptunea amianta), and the 15N, from 10.59‰ (the pelagic gastropod Pterotracheoidea) to 21.36‰ (a polynoid polychaete), indicating the presence of at least three trophic levels and the utilization of a variety of food sources. The 13C differences between trophic groups relying on suspended matter and those feeding on deposited material suggested they use different sources of carbon for their nutrition and the presence of two food webs based on pelagic versus benthic consumption. The community was largely dominated by surface deposit feeders and suspension feeders, a pattern consistent with large fluxes of particulate matter to the OMZ bottoms.

Daichi Yano, Chubu University; Shiro Takei, Chubu University, Aichi Prefecture, Japan; Etsuhiro Muneyama, Yamaguchi University; Hironori Asada, Yamaguchi University, Yamagichi Prefecture, Japan; Masakazu Iwasaka, Hiroshima University; Yuichi Oba, Chubu University

Sunlight that reaches the mesopelagic zone (200 - 1000 m depth) is limited to a narrow blue-green spectra and vertical angle. Fishes inhabiting these depths commonly migrate to shallow waters at night to feed on zooplankton. Lanternfishes (Myctophidae) display counterillumination by ventral photophores bioluminescence emitting downwards light. Contrarily to pigmented filters in other fishes, luminescence of lanternfishes is matched to mesopelagic light spectra by a blue-green inner reflector. Diaphus watasei was captured in harbours of Kochi and Mie Prefectures, Japan. Reflection spectra was analysed on fresh photophores. Light organs were prepared for further analyses on histological structure, luciferase purification, iridophores observed under light microscope, X- ray diffraction and Fourier-transform infrared spectroscopy. Inner reflector is made of exclusive “perfect” hexagonal guanine iridophores, packed in hexagonal interlocking arrangement. This specific pattern was found to ensure simultaneous reflection of light on the same direction while minimizing energetic costs via photon losses in cell gaps. Parabola-like shape of the inner reflector with photocytes on its focus ensures that all light from the photophore is emitted on a vertical angle. Spectra of photocytes light is modulated by the coloured reflector (reflection maximum at 460 – 470 nm) to adapt the camouflage spectra during vertical migrations. Exceptional reflector not only achieves counterillumination by simultaneously matching sunlight spectra and angle but also allow spectral regulation.

Marshall Bowles, Louisiana Universities Marine Consortium; Craig McClain, Louisiana Universities Marine Consortium

A small brine puddle located on the Atwater Valley 340 Lease Block in the northern Gulf of Mexico was explored using a Remote Operated Vehicle (ROV) in an attempt to detect small scale organic enrichment on the periphery of a nutritionally rich chemosynthetic habitat. Push core pairs were taken at shrinking distances from the original brine shoreline (30, 15, 5, 3, 1 and 0 meters). Pairs were analyzed for methane concentrations and macrofauna abundance and diversity. Macrofauna communities were typified by large numbers of cumaceans (an indicator of low O2 habitats), a chemosynthetic bivalve (Bathymodiolus brooksii), and large polychaetes. This generated the typical high biomass-low diversity trend common of chemosynthetic communities. Methane levels in cores ranged from 13 to 266 μM, indicating that seeping fluids within this small brine system were present at greater concentrations than typical deep-sea sediments. During the ROV dive, we noticed that the brine levels had decreased, shrinking the pool in volume and lowering the shoreline. A visible shoreline on the edge of the brine puddle was evident by the color of surficial sediments; sediments above the tide line were brown and flocculent and sediments below the mean tide were pale and gray. This evidence and the observed ebb of brine from the puddle suggests this small system is tidally influenced and sees a range of brine coverage over a normal tidal period. Once the brine level within the depression had ebbed to its lowest level, small islands of sediment emerged from underneath the brine. Once free of the brine’s confines large sediment plumes emanated from one island in particular, Worm Hill. Push cores targeted active burrows on Worm Hill and were found to be home to large echiuran worms that are purple and green with golden hooks (Mardi Gras Spoon Worm). Tidally influenced brine habitats thus may host unique fauna that have adapted to survive prolonged brine exposure.

Kevin Hardy, Global Ocean Designs; Phil Hastings, UC San Diego; Natalya Gallo, UC San Diego

Nearshore submarine canyons are unique features that bring the deep sea close to shore, potentially functioning as highways connecting shallow and deep sea ecosystems. Canyons are keystone structures for local fisheries that provide ecosystem services and are very diverse due to increased environmental variability and proximity to shore. Currently 27% of large canyons in California are protected by government agencies, but this does not include the smaller nearshore canyons, most of which are unprotected and understudied. These are more common in Southern California than Central and Northern California due to differing shelf characteristics along the coast. To evaluate protection of nearshore submarine canyons, we surveyed the bottom topography along a transect 5 km from shore, identifying features that are deeper than 200 m and incised at least 100 m into the slope. Applying this definition, we identified 32 nearshore submarine canyons in the Southern California Bight alone. To better understand the ecology of nearshore submarine canyons, we developed two low-cost, spatially flexible autonomous lander systems: the Nanolander DOV BEEBE and Picolander DOV JEAN. The Nanolander has three spherical housings containing a camera system, an acoustic communication system, as well as a SBE MicroCAT for measuring conductivity, temperature, pressure, and dissolved oxygen over several weeks. The smaller, two-sphere Picolander is equipped with a Zebra-Tech sensor, camera system, and timed release for 24-hour deployments. Both systems are positively buoyant and deployed by hand from a small boat. The landers will collect high-frequency environmental and seafloor community data at depths of 100-500 m in the La Jolla Canyon. Because small autonomous landers collect paired biological, physical, and biogeochemical data in hard to access areas, they can serve as powerful tools to study the unique ecology of nearshore submarine canyons and inform management decisions.

The continued sustainable exploitation of marine resources is dependent on our understanding of marine ecosystems. Benthic communities provide a wide range of ecosystems services which both directly, and indirectly, benefit the management of economically vital sources. By documenting and describing the different biological communities found within Disko bay (western Greenland), this project contributes to the wider MAPHAB project in its creation of high-resolution benthic habitat maps of western Greenland. Here we analyse drop camera footage from 55 different stations covering 18.6km with a depth range of 607m (34m to 641m). We have identified 15 different community types within the bay formed by emergent epifauna including sponges, bryozoa and ascidian beds. We assess the vulnerability of these habitats to trawling impact from widespread fishing in the region. By utilising these maps, marine spatial planners will be able to adjust practises to minimise harm to vulnerable assemblages and maintain the provision of vital ecosystem services.

Guillermo Mendoza, Scripps Institution of Oceanography; Elvira Hernandez, Scripps Institution of Oceanography; Cristina Frieder, University of Southern California; Lisa Levin, Scripps Institution of Oceanography

Oxygen minimum zones (OMZs) play a major role in the global carbon system and strongly influence the distribution of benthic marine communities. Metazoan meiofauna was studied in sediment samples collected by multiple corer off San Diego, southern California to examine the influence of the Oxygen Minimum Zone (OMZ; <0.5 ml L-1) on community structure. Six sites were sampled along a depth transect across the continental margin, spanning from the upper slope above the OMZ (300 m) to the mid continental slope (1200 m) beneath the OMZ. By using meiofauna samples collected during two seasons (July and December) during 2012, we tested the hypothesis that variation in organic matter availability and bottom-water oxygen concentrations would be reflected in changes in meiofaunal community density, composition and vertical distribution in the sediment. Overall, 21 meiofaunal taxa found. Meiofaunal communities along the OMZ did not respond to oxygen thresholds as expected. Mean meiofauna densities (core depth 0-10 cm) ranged from 202 to 456 ind 10 cm-2 in July, and from 235 and 530 ind 10 cm-2 in December respectively. In contrast to other nearby oxygenated sites or other OMZ settings of the eastern Pacific OMZ, where the hypoxic conditions are more intense, unexpectedly low nematode and relatively high copepod densities within the OMZ core (~0.2 ml L-1), were found. Changes in community composition with depth and season may be the result of top-down (nutritional) influences and bottom-up control (macrofaunal predation) as well as other environmental parameters.

Angelina Dichiera, The University of Texas at Austin Marine Science Institute; Kerri Lynn Ackerly, The University of Texas at Austin Marine Science Institute; Andrew J Esbaugh, The University of Texas at Austin Marine Science Institute

Low oxygen environments are becoming more prevalent in global oceans, and this is especially true of the deep ocean environments of the northern Gulf of Mexico. The Gulf of Mexico experiences one of the largest seasonal hypoxic zones in the world, exposing endemic fish to chronically oxygen-limited waters. Work on red drum (Sciaenops ocellatus), a denizen of the Gulf, has demonstrated the ability to dynamically regulate specific hemoglobin (Hb) subunits in response to chronic hypoxia, which results in higher blood oxygen binding affinity and a reduced critical oxygen threshold. Hb isoforms vary in their amino acid sequences that confer varying sensitivities to protons and allosteric modulators and impact the ability to bind oxygen. This work explores red blood cell plasticity and assesses the impacts on maximum metabolic rate tested via intermittent-flow respirometry on fish acclimated to sub-lethal hypoxia. Gene expression profiles measured using qPCR showed up-regulation in hypoxia of one Hb isoform by 3-fold relative to control by 4 d post-exposure with consistent upregulation at all time-points thereafter. Hematocrit showed an increase in hypoxia at 8 d. Red drum do not show changes in the allosteric modulators ATP/GTP at any time point. Changes in Hb expression reduced the magnitude of the Root effect (~25% in normoxia to ~12% in hypoxia), and subsequently increase in oxygen binding at physiologically relevant pHs for hypoxia acclimated fish. Together, these changes correlated with increased maximum metabolic rate and aerobic scope when tested under hypoxia relative to controls. This work suggests that high affinity Hb with small Root effects are more beneficial to fishes exposed to hypoxia. This would suggest that a combination of genetic analyses and in vitro analysis of Hb oxygen binding characteristics can be used to assess the vulnerability of deep-sea fishes to oxygen-limited waters common to the deep sea environment.

Natasha Karenyi, University of Cape Town; Charles Griffiths, University of Cape Town; Kerry Sink, South African National Biodiversity Institute; Lara Atkinson, South African Environmental Observation Network

Deep-water benthic communities have been insufficiently sampled within the South African Exclusive Economic Zone, limiting our understanding of community patterns and their environmental drivers. This study is one of the first to investigate the marine epifaunal communities along the Agulhas ecoregion outer shelf, shelf edge and upper slope of the South African continental shelf. Visual surveys of the seabed were conducted to quantify epifauna using the SkiMonkey III towed benthic camera system during the ACEP Deep Secrets Cruise in September-October 2016. The study area was divided into 29 sites spanning the continental shelf and shelf edge from the tip of the Agulhas Bank to offshore of the Kei River mouth, and ranging in depth from 150-700 m. A total of 855 seabed images were processed, and 163 benthic taxa quantified. In conjunction with the abundance data, a range of environmental variables were used to assess drivers of the biodiversity patterns observed. Data were analysed using multivariate analyses in PRIMER v6. Nine benthic community types were identified based on suites of characteristic species. Spatially, these communities did not separate out well, but their distribution was shown to be strongly influenced by substratum type, trawling intensity, slope, and depth.

Bivalve farming is a type of mariculture done in open sea water on racks, rafts or longlines where naturally occurring phytoplankton serves as a key food item, introduced into the enclosures with the normal circulation of seawater. Increasingly, the reverse trophic interaction is being recognized; dissolved inorganic and organic waste compounds released by metabolically active bivalves can supply phytoplankton with nutrient and energy requirements for their growth. This two–way interaction can be viewed as a type of community symbiosis developed over long evolutionary timescales. The extent to which this affects overall nutrient budgets and thus primary production is related to the system flushing rate and residence time. Here we reviewed the feeding mechanism and nutrient recycling activities of bivalve and also emphasized the role of phytoplankton as a key nutritional live feed in sustainable bivalve mariculture. Bivalves influence nutrient dynamics through direct excretion and indirectly through microbially mediated remineralization of their organic deposits in the sediments. The quantitative knowledge of bivalve - phytoplankton trophic interactions in coastal waters will inform bivalve mariculture development to effectively serve the needs of both seafood production and ecosystem restoration.

Karen Croke, National University of Ireland Galway; Aisling Robinson, National University of Ireland Galway; Eva Turley, National University of Ireland Galway; Louise Allcock, National University of Ireland Galway

Deep-water octocorals are prevalent on the Atlantic margin, but they tend not to be identified to species, because of global difficulties in deep-sea octocoral taxonomy. Our aim was to determine how many species of the suborder Calcaxonia (families Chrysogorgiidae, Primnoidae, and Isididae) are present in Irish waters. We collected tissue samples and morphology vouchers from 74 Isididae, 24 Primnoidae and 20 Chrysogorgiidae colonies during two expeditions of Celtic Explorer to the Irish slope. We extracted DNA and sequenced three mitochondrial gene regions: MutS, COI+igr1, and Nad2. We built haplotype networks from our sequences and a phylogenetic tree which included additional sequences from Genbank. We compared gross morphology using in situ and ex situ photographs of the colonies. DNA sequence variability was very low, as found previously for octocorals. We concluded that a species never had more than one molecular haplotype, but that some haplotypes were representative of more than one species. We found 23 haplotypes of Isididae, ten haplotypes of Primnoidae, and five haplotypes of Chrysogorgiidae. We were able to confidently assign species names to a few haplotypes, genus names to most primnoids and chrysogorgiids, whereas the Isididae (bamboo corals) require future detailed morphological studies including SEM of sclerites.

Julia Andrews, FSU; Amy Baco, FSU

The deep-sea precious red coral Hemicorallium laauense has long been overharvested in the North Pacific for jewelry and curio trades. An understanding of the population structure and connectivity of these corals has been limited due to the difficulty of sampling and taxonomic challenges within the Family Coralliidae. We report on population genetics of 270 H. laauense individuals from 16 populations throughout the Main Hawaiian Islands and the Northwestern Hawaiian Islands (NWHI). We focus on sites having no known history of commercial harvest, to provide better baseline population structure data. Nine microsatellite loci were found, with a range of 14–74 alleles per locus. Observed heterozygosity (0.46–0.92) was generally lower than expected (0.68–0.98) except for one locus. Global FST was low (0.018) as were pairwise FST values (0.013–0.078), but this metric is likely affected by the high level of variation of alleles within populations. Global G'ST (0.166) and pairwise values were higher (-0.003–0.489), and maximum likelihood GST indicated significant differentiation between populations (p=0.01). DAPC showed a pattern of separation of the Main Hawaiian Islands from the NWHI, though samples from Kaena Point appear to form their own cluster. Membership assignments showed moderate admixture between some locations, while East and West Northampton and Raita Bank showed almost no admixture. Mantel tests showed no isolation by depth. IBD was found through a more sensitive dbRDA model. These results suggest a level of connectivity between distant locations, yet within the Hawaiian Ridge some features are more isolated. The inconsistent connectivity of these corals is likely amplified by their patchy distributions. Connectivity within this large area suggests these corals could also be connected to areas where trawling and harvesting have diminished coral populations, but these sites should not be relied upon as source populations without further study.

Austin Boutilier, Florida Atlantic University; April Cook, Nova Southeastern University; Tracey Sutton, Nova Southeastern University

Barreleyes (Opisthoproctidae) are members of a family of infrequently-caught, deep-sea, pelagic fishes. Three species of this family were previously known to inhabit the Gulf of Mexico (Dolichopteroides binoncularis, Dolichopteryx longipes, and Monacoa grimaldii). Five more species have now been documented to also inhabit the northern Gulf of Mexico deepwater ecosystem (Bathylychnops brachyrhynchus, Dolichopteryx rostrata, Opisthoproctus soleatus, Rhynchohyalus natalensis, and Winteria telescopa). Discrete depth sampling by MOCNESS nets provided depth information for some captures. Previously considered a rare species with a capture in the Bahamas (type specimen) and a few in the northeastern Atlantic, Bathylychnops brachyrhynchus was found in moderately high numbers in the Gulf of Mexico and at larger sizes than were previously known to occur.

Minin Kirill, Shirshov Institute of Oceanology, Russian Academy of Sciences; Sergey Galkin, Shirshov Institute of Oceanology; Alexey Udalov, Shirshov Institute of Oceanology; Margarita Chikina, Shirshov Institute of Oceanology; Dmitriy Frey, Shirshov Institute of Oceanology; Olga Golovan, National Scientific Center of Marine Biology FEB RAS; Valeria Soshnina, Russian Federal Research Institute of Fisheries and Oceanography; Nikolai Neretin, White Sea Biological Station, Moscow State University; Vassiliy Spiridonov, Shirshov Institute of Oceanology

During 79th cruise of RV Akademik Mstislav Keldysh twelve trawl hauls were collected in the Powell Basin (northwestern Weddell Sea) and adjacent area at depths 370–3771 m. The structure of the benthic assemblages was highly variable when considered at the macrotaxon level. The main factors shaping the taxonomical structure of the sampled assemblages were depth, near-bottom current velocities and proportion of the hard fraction of the sediment. Hard substrate assemblages of the Antarctic peninsula slope and Philip Ridge with high percentage of filter-feeders (mainly sponges) were associated with the highest values of the near-bottom tide currents (up to 55.6 cm/s). In several trawl hauls indicator species of vulnerable marine ecosystems (mainly demospongian sponges, deep-sea hydrocorals Stylasteridae and octocorals (Primnoidae) (were collected.

Simon Harris, British Geological Survey

The ecosystem dynamics of benthic communities depend on the relative importance of organism reproductive traits, environmental factors, inter-specific interactions and mortality processes. The fine-scale community ecology of sessile organisms can be investigated using spatial point process analyses (SPPA) and Bayesian network inference (BNI) because the position of the specimens on the substrate (their spatial positions) reflects the biological and ecological processes that they were subject to in-life. Here we use these analyses to investigate the ecology of deep-sea glass sponge dominated community "The Forest of the Weird" (2442m depth, Ridge Seamount, Johnston Atoll, Pacific Ocean). A 3D reconstruction was made of this community using photogrammetry of video stills taken from high-resolution ROV video. The community was dominated by two genera of Hexactinellids with octocorals also present in large proportions. SPPA of the dead versus alive organisms revealed a random distribution of dead amongst the living, showing a non-density dependent cause of death for the majority of taxa, apart from the Aspidoscopulia high-density ridge crest region. SPPA showed that the glass sponges and octocorals were most strongly influenced by different underlying processes, and reacted to the environmental conditions differently. The octocorals responded to higher density areas with increased intra-specific competition, whilst the glass-sponges seemed impervious to a doubling of specimen density. To our knowledge, this study is the first to analyze the mortality, population and community dynamics of a deep-sea sponge community using spatial point process analyses. Our results provide the first insight into the variety of ecological behaviors of these different glass sponges and octocorals, and show how these different organisms have developed diverse responses to the biological and environmental gradients within their habitat.

Tracey Sutton, Nova Southeastern University

Deep-living pelagic organisms facilitate key ecosystem processes within the pelagic realm, particularly with regards to the movement of carbon and energy via the biological pump. The characteristic pattern of diel vertical migration (DVM) conducted by deep-living pelagic fauna involves remaining at mesopelagic depths (c. 200 – 1000 m) through daylight hours, then migrating to epipelagic depths (0 – 200 m) at night to feed. However, there is considerable variability in DVM patterns amongst migrants, with some species migrating every night (“obligate migrants”), and others migrating less frequently (“partial migrants”). While DVM amongst obligate migrants is likely driven by inherent biological requirements (e.g., circadian rhythms or energetic necessity), partial migrants appear to have more choice over whether or not to migrate. Here, we analyse an extensive, spatially and temporally-explicit collection of >250,000 mesopelagic fishes from the northern Gulf of Mexico (2011 - 2017) to demonstrate a novel statistical method for quantifying DVM behavioural patterns within the 55 most-abundant species, and to examine biological (e.g., ontogenetic) and environmental (e.g., mesoscale hydrography) patterns of DVM behaviours within those species identified as “partial migrants”. We anticipate that the findings from this study will provide valuable insight into the behavioural rules governing DVM amongst mesopelagic fishes, and improving predictions of carbon flux through this poorly-known, but critical, component of the biological pump.

Emyr Martyn Roberts, University of Bergen; Natural Resources Wales; Andrew Davies, University of Rhode Island; Joana Xavier, University of Porto - CIIMAR; Hans Tore Rapp, University of Bergen; NORCE, Norwegian Research Centre

The Schulz Bank is a deep-sea seamount located on the Arctic Mid-Ocean Ridge. It has a large depth gradient, extending from 2500 to 560 m at the summit, and is subjected to a complex oceanographic setting that is thought to influence the sponge ground present. While recent studies revealed the summit is host to a dense sponge ground community made up of large demosponges, glass sponges, ascidians, and anthozoans, the extent of the sponge ground remains unknown and a complete investigation of the entire Schulz Bank megafauna community has yet to be reported. Here, we used remotely operated vehicle (ROV) footage to investigate changes in the community structure with depth. We found distinct faunal communities on the basin, slopes, and summit. Mobile and opportunistic taxa were most abundant in the soft bottom basin. Smaller demosponges like Geodia hentscheli and glass sponges dominated the slopes; whereas, large structure-forming sponges (e.g. Geodia parva, Stelletta rhaphidiophora, and Schaudinnea rosea) and ascidians characterized the summit. Species richness and density was greatest at the summit. Environmental variables, such as water current speed, substrate type, nutrient availability, and water mass properties, are likely influencing the community patterns observed.

Loïc N. Michel, IFREMER; Michel Segonzac, Museum National d'Histoire Naturelle (MNHN); Marie-Anne Cambon-Bonavita, IFREMER; Florence Pradillon, IFREMER

Among hydrothermal vent species, Rimicaris exoculata is one of the most emblematic, hosting abundant and diverse ectosymbioses that provide most of its nutrition. Rimicaris exoculata co-occurs in dense aggregates with the much less abundant Rimicaris chacei in many Mid-Atlantic Ridge vent fields. This second shrimp also houses ectosymbiotic microorganisms, but has a mixotrophic diet. Recent observations have suggested potential misidentifications between these species at their juvenile stages, which could have led to misinterpretations of their early life ecology. Here, we confirm erroneous identification of the earliest stages, and propose a new set of morphological characters unambiguously identifying juveniles of each species. On the basis of this reassessment, combined use of C, N and S stable isotope ratios reveals distinct ontogenic trophic niche shifts in both species, from photosynthesis-based nutrition before settlement, towards a chemosynthetic diet afterwards. Furthermore, isotopic compositions in the earliest juvenile stages suggest differences in larval histories. Each species thus exhibits specific early life strategies that would, without our re-examination, have been interpreted as ontogenetic variations. Overall, our results provide a good illustration of the identification issues persisting in deep-sea ecosystems and the importance of integrative taxonomy in providing an accurate view of fundamental aspects of the biology and ecology of species inhabiting these environments.

Greg Rouse, Scripps Institute of Oceanography University of California San Diego

Crinoidea (sea lilies and feather stars) is the least understood of the five living echinoderm classes and includes the fewest described species (~660). However, the group remains undeservedly obscure. Here, we report the growing body of research that reveals the importance of crinoids across a wide range of deep-sea marine habitats. Remotely operated vehicle and submersible dives reveal that crinoids may occur at high densities, constitute locally dominant benthic invertebrate megafauna, and contribute to three-dimensional habitat frameworks in both Atlantic and Pacific oceans. These operations have also extended geographic and bathymetric distributions of described taxa and discovered new species. Unfortunately, the taxonomy required for understanding their ecological contributions remains imperfect. Although recent molecular phylogenies have supported some morphologically-based taxa at generic through ordinal levels, they have rendered others paraphyletic and polyphyletic. Similarly, whereas earlier species-level taxonomy suffered from poor understanding of ecophenotypic and ontogenetic variability and resulted in over-splitting, sequence data has revealed morphologically indistinguishable cryptic species. We are currently undertaking revisions at all categorical levels and searching for phylogenetically robust morphological features that will also apply to fossil taxa.

Amy Baco, Florida State University

Vertical patterns of distribution in deep-sea fishes on seamounts have recently been documented to show strong changes in assemblages with depth, while horizontal variability patterns within a single seamount and among seamounts remain drastically understudied. Papahānaumokuākea Marine National Monument is a part of an extensive seamount chain that provides relatively unimpacted deep-sea ecosystems as well great variability in physiographic and oceanographic characteristics. Three seamounts: Necker Island, French Frigate Shoals, and Pioneer Bank were explored in this area using AUV surveys to document the deep-sea fish assemblages and their horizontal patterns of distribution at three different depths. Comparisons were made at a given depth among sides of the seamount and among the three seamounts. Stomiiformes were the most abundant order with the highest number of individuals at 300 and 450 m, and the highest abundance on French Frigates. At 600 m, Myctophiformes showed the highest number of individuals overall and were most abundant on Necker. Significant differences in abundance by side, seamount, and the interaction were observed at 300 and 600 m. Significant differences in some diversity metrics occurred in one, both or the interaction of the factors of seamount and side at each depth. At all depths, the fish assemblage structure showed a significant variation among sides and seamounts that was explained mostly by the interaction term. The most common environmental factors related to assemblage structure at all depths were temperature, % sand, slope, rugosity, direction of the substrate, current vectors u and v, chla-a, POC, and time of day. These results show significant horizontal variability in deep-sea fish abundance, diversity, and assemblage structure both within and among seamounts. The results obtained in this study provide baseline data that can be taken into consideration for management and conservation in the Monument and other seamount chains.

Amy Baco, Florida State University

Knowledge of deep-sea fish assemblages and their spatial variation is a critical gap in our understanding of seamount ecology and is relevant to designing deep-sea marine protected areas. Pioneer Bank is a seamount located in the Northwestern Hawaiian Islands that has been protected since 2000 as part of the Papahānaumokuākea Marine National Monument. There are no published studies on either shallow or deep water ecosystems on this seamount and the seamount has no history of human impacts, thus it is a good location to describe spatial variation in deep-sea fish assemblage structure, including abundance and diversity as well as variability in relation to environmental parameters. Using AUV photos, 81 species were identified on three sides of Pioneer at depths of 300, 450 and 600 m. The fish assemblages were dominated by Gadiformes, Perciformes and Stomiiformes. Relative abundance of fishes was significantly different among sides of the seamount and the interaction of side and depth, with the NW side having the highest relative abundance at 450 m. Species richness, rarefaction, Shannon diversity and Simpson dominance showed significant differences between the S and NW side; with the S side having the lowest diversity and high dominance. The fish assemblage structure had significant differences among both sides and depths, with depth as the most important factor in the explanation of the model. Fish assemblage structure was most strongly correlated with dissolved oxygen. These scales of spatial variability both with depth and across short horizontal distances on a single seamount are similar to those found on the nearby seamount, Necker Island, and on other seamounts, which reaffirms the spatial variation in deep-sea fish assemblages on these underwater features. This study provides an ecological baseline for the management and conservation of seamounts in the Monument and other areas.

Adrian G. Glover, Life Sciences Department, Natural History Museum, London; Daniel O. B. Jones, National Oceanography Centre; Steve Persall, UK Seabed Resources Ltd., Sunnyvale, USA; Erik Simon-Lledó, National Oceanography Centre; Craig R. Smith, University of Hawai'i at Manoa; Kerry L. Howell, School of Biological and Marine Sciences, University of Plymouth

Although abyssal plains are the largest habitat on earth, this environment remains poorly studied. Using an extensive archive of historic image data collected in the 1970s from across the Clarion-Clipperton Fracture Zone (CCZ), we explored patterns in the composition, life-history traits and diversity of epibenthic megafauna and xenophyophores across nine transects, covering a total of 7,200m2 within a large area of the abyssal CCZ rich in polymetallic nodules. This study observed 90 morphotypes, across nine phyla, with nearly 20 times greater density of xenophyophores than megafauna. By abundance, 72% of megafauna were suspension feeders, 60% were associated with nodules, 65% were sessile and 79% were rare morphotypes (fewer than 10 records). Similar patterns were observed in the xenophyophore community, with 100% sessile organisms and 63% nodule-associated. Rare, nodule-associated, suspension feeding and sessile organisms thus formed a large proportion of the CCZ megafauna and xenophyophore communities. In addition, while the dominant taxa appeared homogenous over large scales (> 1,000 km), there was high turnover of rare morphotypes, suggesting that many morphotypes either have a very limited geographic extent or occur at very low densities (although confidence in determining species ranges with morphotypes is limited). A significant proportion of the variation in megafauna diversity between sites was explained by broad-scale topographic features, providing support for the inclusion of these variables in predictive modelling and spatial planning at a broad, regional scale (1,000s km). Predictive modelling could play a role in supporting spatial planning in the CCZ where biological data are limited.

Caitlin Feehery, Scripps Institution of Oceanography, UC San Diego; Greg Rouse, Scripps Institution of Oceanography, UC San Diego

Bathymodiolus Kenk and Wilson, 1985 includes fourteen currently recognized species from deep-sea chemosynthetic environments in the Pacific, Atlantic, and Indian oceans. In this study, phylogenetic analyses of mytilid mussels sampled from seeps along the Costa Rica margin reveal the presence of three new Bathymodiolus species, sampled from depths across ~1000-1900 meters. Bathymodiolus billschneideri n. sp., B. earlougheri n. sp., and B. nancyschneiderae n. sp. differ genetically from congeneric species of Bathymodiolus and show some stratification by depth. The depth ranges of Bathymodiolus billschneideri n. sp., B. nancyschneiderae n. sp., and B. earlougheri n. sp. were ~1400-1900 m, 1000-1100 m, and ~1000-1900m, respectively. Bathymodiolus billschneideri n. sp. and B. earlougheri n. sp. were found to be closely related to Bathymodiolus thermophilus Kenk and Wilson, 1985, while B. nancyschneiderae n. sp. exhibited closer relationships to non-East-Pacific taxa. Bathymodiolus thermophilus was the first Bathymodiolus mussel discovered, sampled from a vent along the Galápagos Rift Zone in 1985 and later recorded along much of the East Pacific Rise. This study also confirms the presence of B. thermophilus at the Costa Rica margin, representing the first DNA and morphological samples of B. thermophilus at a seep environment. Analysis of habitat evolution suggests that B. thermophilus and its closest relative, B. antarcticus Johnson & Vrijenhoek, 2013, are of seep ancestry.

Jozée Sarrazin, Ifremer; Marjolaine Matabos, Ifremer; Eva Ramirez-Llodra, REV ocean / NIVA; Riwan Leroux, Trois-rivières Québec University ; Stephane Hourdez, Observatoire Océanologique de Banyuls-sur-Mer; Cécile Cathalot, Ifremer; Agathe Laes-Huon, Ifremer; Ana Colaço, MARE

Understanding colonization processes is particularly essential to assess the natural regeneration capacity of vent communities in response to a disturbance. To identify the environmental and biological processes governing the recovery of benthic communities inhabiting the active vent edifice Montségur and two surrounding habitats, we implemented an innovative experimental project based on an induced disturbance. A total of 12 experimental and 5 reference quadrats were deployed at three targeted habitats on the Lucky Strike vent field, Mid-Atlantic Ridge : (1) on Montségur, (2) at a sedimented peripheral area and (3) at an inactive chimney. A disturbance was induced on each quadrat by removing all visible fauna. Then, we monitored the recolonisation dynamics of the benthic communities in terms of macrofaunal diversity, density, faunal composition and population size structure over two years. At the active vent site, the taxonomic richness was not significantly different from pre-disturbed communities one and two years after the disturbance. However, the total density of organisms was significantly lower, with a recovery rate ranging from 16% to 68%, 1 year post-disturbance and from 20% to 79%, two years after the disturbance in comparison to baseline communities. In addition, the structure of faunal communities after the disturbance was significantly different than that of the baseline communities, with a higher evenness of distribution among different species. Indeed, we noticed a decrease of the relative abundance of some typical vent species coupled with an increase of some gastropod species, suggesting a key role of biotic factors in shaping more mature vent communities. To complete the picture, these recovery rates should be investigated at much larger spatial (>1m) and temporal (>2 years) scales to better understand the resilience of active and inactive communities and propose restoration methods that will help protecting the unique fauna they harbour.

David Kerstetter, Nova Southeastern University; David Wyanski, South Carolina Department of Natural Resources, Marine Resources Research Institute; Tracey Sutton, Nova Southeastern University

The most abundant fishes on Earth live in the meso- and bathypelagic (deep-pelagic, collectively) zones of the open ocean, where they play a key role in deep-sea food webs by mediating energy flow from surface waters to great depth. Of these fishes, the most speciose taxon is the family Stomiidae (dragonfishes). Despite being the numerically dominant predators of the global mesopelagic zone, stomiid reproductive ecology is poorly known. Research surveys rarely catch larger adults, impeding reproductive ecology studies. Between 2010 and 2011, the Offshore Nekton Sampling and Analysis Program sampled the Gulf of Mexico using a research-sized, opening/closing trawl (10-m2 MOCNESS) and a commercial-sized, high-speed rope trawl (HSRT). Size-distribution analysis by gear type revealed: the HSRT caught more specimens per species, and the HSRT caught significantly larger specimens, whereas the MOCNESS sampled more juveniles. Gonads were dissected from 714 individuals representing 47 species, and the 12 dominant species were analyzed in further detail. Gonadal histology assessment indicated that stomiids are gonochoristic and exhibit asynchronous oocyte development and batch spawning. A total of 11 of the 12 species had sex ratios that did not significantly differ from a 1:1 (male:female) ratio (P < 0.05). Histological analysis indicated that females mature at larger sizes than males. Given the lack of age and growth data for this family, these data are critical for estimating stomiid production rates, a key element for quantifying the role of stomiids in the transfer of organic matter within the deep-pelagic zone, the planet's largest cumulative ecosystem.

Laura Garzoli, CNR-IRSA Verbania; Ryan Young, NUI Galway; Louise Allcock, NUI Galway; Maria Tuohy, NUI Galway; Mary Murphy, NUI Galway

Fungi have been isolated from almost any kind of marine substrate, from decaying woods to sessile animals, plants or algae and from shallow to deep habitats. Despite their wide distribution in the marine environment and estimates ranging between ten thousand and ten million species, only ~1,600 were described to date. Description of fungal communities associated to new habitats is critical to understand their magnitude in the marine environment and confirm their ecological roles. In this study we investigated the fungal biodiversity associated to deep sea sediment sampled at the western edge of the Porcupine Bank, and deep sea coral and sponge sampled at three main reefs in the Whittard Canyon. Samples were inoculated on five media, incubated at 5˚C and 24˚C and routinely checked for germination. Species identification was performed using both molecular and morphological analyses. The overall deep sea fungal community consisted in 87 isolates belonging to 47 fungal species and 24 families. Sixty-three isolates were obtained from 19 out of 20 sediment samples while 24 isolates were obtained from 12 out of 24 animal samples. Two fungal species, Cladosporium ramotenellum and Penicillium antarcticum were detected on both substrates. Predominant was the phylum Ascomycota and families Eurotiomycetes, Dothideomycetes and Sordariomycetes; confirming what previously detected in the marine environment. A putative new fungal species of the family Arachnomycetaceae was identified through phylogenetic analyses. Multivariate statistics highlighted two significantly different microbial communities associated with sediment or animal. Fungal ecological roles analysed with FUGUild tool showed predominance of saprotrophic species associated to sediment and predominance of symbionts associated to animals. Our study represents the first mycological investigation of cold water coral reefs worldwide and the first described mycobiota from the European Continental Shelf western margin.

Jose Maria Quintanilla, Instituto Espanol de Oceanografia; Raul Laiz-Carrion, Instituto Espanol de Oceanografia; Trika Gerard, NOAA NMFS

Atlantic bluefin tuna (ABFT), Thunnus thynnus is an oceanic top predator that undertakes long distance migrations from its common feeding grounds in the NE Atlantic. As adults, ABFT is an important fishery resource worldwide, however during the larval stage it is a key species in the corresponding ecosystems of its two well established spawning areas: the Gulf of Mexico (GOM) and the Balearic Sea (MED). Trophic studies using stable isotopes analysis (SIA) have proven useful in marine food webs and have been used to compare larval ABFT isotopic signatures in each spawning area. During the first few days of life (preflexion ontogenetic stage), the SIA signature obtained via maternal transmission predominates in larval ABFT. We estimated values for the maternal isotopic signature from the early larval stages from a concurrent trophic study (Quintanilla et al. 2019). For the first time, daily increment growth and otolith biometry were analyzed along with nitrogen SIA (δ15N) for preflexion ABFT larvae. These values were compared for the GOM and MED during the same spawning season (2014). Larvae were split in two groups: an optimum growth and a less efficient growth using residual analysis. We found significant intra-population differences with higher growth rates and larger otoliths that showed wider increments associated with lower values of δ15N. The two groups had a direct relationship between growth potential and δ15N at preflexion larval stages for each spawning area. These results point to the importance of the maternal isotopic signatures observed in faster larval growth associated with lower δ15N values. Faster growth during the early life stages can improve overall larval survival and may represent a key maternal legacy for this species.

Jason Mostowy, Texas A & M University at Galveston; Leif Rasmuson, Oregon Department of Fish and Wildlife; Trika Gerard, NOAA NMFS; Lourdes Vasquez Yeomans, El Colegio de la Frontera Sur, Chetumal; Eloy Felipe Sosa Cordero, El Colegio de la Frontera Sur, Chetumal; Laura Carrillo, El Colegio de la Frontera Sur, Chetumal

The invasion of the western Atlantic by the Indo-Pacific lionfish (Pterois volitans/miles) represents a serious threat to the ecological stability of the region. The early life history of this predator remains poorly understood despite the important role of larval supply in reef fish population dynamics. In this study, we characterized spatiotemporal patterns in the distribution of larval lionfish collected in the western Caribbean, US Caribbean, and the Gulf of Mexico from a number of ichthyoplankton surveys conducted between 2009-2016. Using generalized additive models (GAMs) we assessed the relative influence of oceanographic and temporal variation on the distribution of lionfish larvae. We also examined otoliths to determine larval ages and to develop growth rate estimates. Ages ranged from 4 to 17 days while mean growth rates were 0.47 mm/day. Lionfish larvae were present at 7.4% of all stations sampled, and preliminary GAM results suggest that lionfish presence is associated with warmer surface waters and the lunar cycle. Year and location also strongly affected the larval distribution, likely a result of the ongoing expansion of the species during the sampling timeframe. Much of the variation in larval lionfish presence remained unexplained, and future studies can incorporate additional environmental factors that may enhance the predictive capabilities of the model. This study improves our understanding of the complexity of the lionfish larval stage and accentuates the need for further research into the early life history of this invasive species. The design and implementation of effective long-term lionfish control mechanisms will require a complete understanding of their life cycle.

Evert de Froe, NIOZ Royal Netherlands Institute for Sea Research; Furu Mienis, NIOZ Royal Netherlands Institute for Sea Research; Marc Lavaleye, NIOZ Royal Netherlands Institute for Sea Research; Beauchard Olivier, NIOZ Royal Netherlands Institute for Sea Research; Anna van der Kaaden, NIOZ Royal Netherlands Institute for Sea Research; Boris Koch, AWI Alfred Wegener Institute for Polar and Marine Research; Karline Soetaert, NIOZ Royal Netherlands Institute for Sea Research; Dick van Oevelen, NIOZ Royal Netherlands Institute for Sea Research

Cold-water coral (CWC) reefs create deep-sea hotspots of metabolic activity, but their organic matter (OM) mineralization by far exceeds local OM deposition from the vertical particle flux. In the present study, we approach this mismatch, and identify potential drivers of the highly active reef communities. The highest diversity of the reefs is associated with the dead degrading coral framework. Video images collected along a transect across the ~700 m- deep Haas Mound, Rockall bank (NE Atlantic), revealed that degrading framework covers 50% of the reef surface. Sampled framework was visually classified as less- and more degraded framework (LF, MF), which harboured different communities. The sessile and mobile macrofauna appear more attracted to the intact surface of the LF, while the porous MF is characterized mostly by cryptic fauna and microorganisms inside the framework branches. LF and MF metabolic activity and organic matter uptake, mineralization and recycling were investigated in (a) incubations in natural reef water, and (b) feeding experiments with 13C-tracer-enriched phytodetritus and 13C-dissolved organic matter (DOM). We found that the LF and MF communities contribute substantially to the reef metabolic activity, likely driven by (1) effective filtration of phytodetritus by the suspension-feeding community and the porous framework matrix, in combination with (2) efficient recycling of DOM by the entire framework community, and (3) recycling of fauna-produced ammonium by the MF microbial community. The CWC reef framework hence creates a huge filtration and recycling plant, similar to an aquarium filter; however, the framework is particularly vulnerable to ocean acidification, which may jeopardize this fine-tuned reef functioning.

Bridget Sparrow-Scinocca, Imperial College London; Martin Blicher, Greenland Institute of Natural Resources; Nanette Hammeken Arboe, Greenland Institute of Natural Resources; Mona Fuhrmann, Zoological Society of London; Kirsty Kemp, Zoological Society of London; Rasmus Nygaard, Greenland Institute of Natural Resources; Karl Zinglersen, Greenland Institute of Natural Resources; Chris Yesson, Zoological Society of London

The term vulnerable marine ecosystem (VME) was introduced to facilitate the spatial management of deep-seas, identifying those habitats vulnerable to anthropogenic disturbance, such as trawling. Consistent interpretation of the VME definition has been hampered by an underlying paucity of knowledge about the nature and distribution of deep-sea habitats. Photographic and video platforms yield data rich, quantifiable imagery to address these knowledge gaps. A low-cost towed benthic video sled has been used to investigate deep-sea habitats and trawling impacts in west Greenland. A review of imagery from multiple cruises highlighted an area where benthic megafauna contributes to notable structural complexity on the continental slope of the Toqqusaq Bank. Quantitative analysis of imagery from this area provides the first description of a soft coral garden habitat and other communities. The coral garden and observed densities are considered in relation to the FAO VME guidelines and wider literature. The study proposes a 486 km2 area spanning ~60 km of continental slope as a VME. This has direct implications for the management of economically important deep-sea trawl fisheries, which operate on the western and eastern boundary of the proposed VME area. This furthers our knowledge and understanding of VMEs in North Atlantic, in a previously understudied region and demonstrates the utility of a low-cost video sled for identifying and describing VMEs.

Chong Chen, Japan Agency for Marine-Earth Science and Technology (JAMSTEC); Hiromi Kayama Watanabe; Shinsuke Kawagucci; Tetsuya Miwa; Hiroyuki Yamamoto; Shinji Tsuchida; Yoshihiro Fujiwara, JAMSTEC

Deep-sea environments are highly dynamic through space and time, but continuous observation over extended periods remains challenging. The monitoring of underwater soundscapes has been proposed as a rapid and cost-effective way to assess the community structure and population dynamics of marine soniferous animals. This passive sensing technology can also produce information associated with the surrounding geophysical environment and anthropogenic activities. From July 2019 to March 2020, we deployed autonomous sound recorders on baited cameras, the Edokko MARK I, and other seafloor observation platforms of JAMSTEC to collect underwater sounds from multiple deep-sea habitat types with a bathymetric range between 250 m to 5500 m deep. The spectral characteristics of deep-sea soundscapes significantly varied among habitats. In coastal regions, soundscapes at Tohoku waters (250 – 1011 m) and Sagami Bay (1700 m) were dominated by shipping noise. At the 1385 m deep Suiyo Seamount vent field, soundscapes were characterized by low-frequency sounds (<100 Hz) from venting orifices. Even at 5500 m deep, we could still detect sounds produced from soniferous fish and cetaceans. Habitat-specific soundscapes are likely important for the dispersal and settlement of deep-sea larvae and should be carefully monitored, especially in habitats attracting mining interests such as vents. To further utilize soundscapes as a tool of deep-sea conservation, we urge for an international collaboration that aims to acquire long-duration recordings from both healthy ecosystems and those disturbed by anthropogenic activities.

Maria Baker, National Oceanography Center, University of Southampton; Kristina Gjerde, IUCN, DOSI; Elva Escobar, Universidad Nacional Autonoma de Mexico; Harriet Harden-Davies, University of Woolongong and Tufts University; Hannah Sharman, University of Southampton

In a world and time faced with challenges on multiple fronts, we deep-sea scientists often wonder how what we do can be meaningful, relevant or even transformative. Where deep-sea science was once an esoteric domain, today it can help tackle the rapidly growing challenges facing society of climate change, biodiversity extinction, habitat degradation, novel viruses and more. This decade, significant decisions will be made that affect the deep ocean - from resource extraction and biodiversity to contaminants and conservation. In this context, science diplomacy is an essential vehicle for conveying critical deep-sea science to managers and policy makers in a way that can enhance and influence decision-making, and vice versa. The Deep-Ocean Stewardship Initiative (DOSI) assembles experts into working groups to assimilate and translate to policy the leading scientific research in 10 priority areas: Minerals Mining, Oil and Gas, Fisheries, Climate, Deep-sea Tailings Disposal, Biodiversity Beyond National Jurisdiction, Marine Genetic Resources, Pollution and Debris, Decade for Ocean Science and New Technology. With official observer status at many international proceedings, including the United Nations, DOSI injects science where it counts the most. We will present DOSI-inspired examples of how science can make a difference, and how scientists from all career stages can directly participate in this process. Beyond the reward of making science count, the communication skills and contacts built through working at the science-policy interface can help advance careers and broaden our horizons.

Laura Robson, Joint Nature Conservation Committee; Liam Matear, Joint Nature Conservation Committee; Harvey Tyler-Walters, Marine Biological Association of the UK; Samantha Garrard, Marine Biological Association of the UK

The Canyons Marine Protected Area (MPA) is located in the south-west corner of the UK’s continental shelf and contains two large canyons that indent the shelf break, adding to the topographic complexity of the seafloor. The MPA includes protection for four deep-sea habitats: cold-water coral reefs, coral gardens, sea-pen and burrowing megafauna communities and the deep-sea bed. The Joint Nature Conservation Committee (JNCC) has a statutory remit for the MPA and provides advice on the conservation and management of the site, specifically on the potential impacts of activities and associated pressures on the protected features, and methods to mitigate against these. A key gap in our understanding, however, relates to the sensitivity of the MPA features to pressures associated with climate change and the functional role of MPA features in supporting mitigation and adaptation to climate change. To address this, a Defra-funded project led by JNCC and the Marine Biological Association of the UK, assessed the sensitivity of deep-sea biotopes comprising The Canyons MPA features, to two climate change pressures: ocean warming and ocean acidification. Benchmarks for these pressures were developed using greenhouse gas emission scenarios, based on a range of climate change projections. Existing literature was reviewed to assess the resistance and resilience of the key species associated with each biotope, and therefore their sensitivity to these pressures. Biotope assessments were then aggregated to MPA feature-level, enabling an overall understanding of potential sensitivities of The Canyons MPA features to ocean warming and acidification. This evidence could be used to support decision-making around adaptive management of MPAs in relation to climate change, in the context of the wider marine environment.

Stéphane Hourdez, UMR 8222 CNRS-Sorbonne Université, LECOB, France; Loïc Michel, Ifremer, Laboratoire Environnement Profond (REM/EEP/LEP), France; Marie-Anne Cambon-Bonavita, 2 Ifremer, Univ Brest, CNRS, UMR6197, Laboratoire de Microbiologie des Environnements Extrêmes (REM/EEP/LM2E), France; Florence Pradillon, Ifremer, Laboratoire Environnement Profond (REM/EEP/LEP), France

The cryptic gastropod genus Alviniconcha (Provannidae) is one of the most emblematic hydrothermal-vent taxa from the Central Indian Ridge and the Southwest (SW) Pacific, inhabiting the walls of active chimneys. Alviniconcha possess species-specific chemosymbiotic bacterial assemblages in their gill, thought to be their principal source of nutrition. SW-Pacific species A. kojimai, A. boucheti – and to a lesser extent A. strummeri – regularly co-occur within a single vent field and in rare instances, the same edifice. These proximate but discrete distribution patterns appear to align with distinct geothermal fluid emissions, suggesting host-specific symbiont compositions somehow enable the partitioning of energetic resources. However, knowledge gaps concerning the functional anatomy of Alviniconcha – documented in the type species only – undermine our capacity to validate this hypothesis. Using specimens of all three species collected from neighbouring vents located off the Wallis and Futuna Islands (North of Fiji), this research examines the host’s role, if any, in habitat partitioning by assessing the presence of host-specific adaptive traits and provides preliminary data on bacterial assemblages in several alimentary tissues, described for the first time. Gill symbioses are similar to previously published data. Notable compositional and phylogenetic differences between gill, foregut and midgut bacterial assemblages provide evidence for at least one mode of symbiont assimilation. Classical and CT-derived anatomical data reveal all species to be highly adapted to a chemosymbiotic lifestyle and functionally synonymous. Subtle differences in host morphoanatomy, though highly useful for species identification, are unlikely to influence habitat partitioning. The current study therefore further corroborates the hypothesis that symbiont-mediated physiological factors are determining host distributions, with evidence of one mode by which symbionts are being assimilated.

Kazuaki Yamaguchi, RIKEN; Mitsumasa Koyanagi, Osaka City University; Akihisa Terakita, Osaka City University

Elasmobranchs (sharks and rays) consist of more than 1200 species, and their habitats range from coral reefs to deep seas. As fundamental resources for molecular studies of elasmobranchs, we previously reported a comprehensive genome-wide analysis on three shark species (Hara et al., 2018. Nat. Ecol. Evol. 2: 1761-1771) and released associating sequence data at the online archive Squalomix (https://transcriptome.riken.jp/squalomix/). This study revealed the repertories of genes potentially responsible for homeostatic controls, vision, and olfaction in shark genomes. We are extending our study on these genes of more diverse elasmobranch species, with an exhaustive search of potential homolog and phylogenetic analysis. For visual opsins, we performed a spectroscopic analysis using synthetic peptides to obtain their absorption spectra. Our phylogenetic analysis indicated the absence of three visual opsin genes (Rh2, SWS1, and SWS2) from the genome of the whale shark Rhincodon typus, while we identified the orthologs of rhodopsin (RHO) and long wavelength-sensitive (LWS) genes. Also, the cloudy catshark (Scyliorhinus torazame) was shown to have lost all visual opsin genes but the RHO ortholog. Our spectroscopic analysis of the RHO pigments revealed blue-shifted spectra for the whale shark (478 nm) and the cloudy catshark (484 nm), suggesting the adaptation to deep-sea vision with dim light. Our result was consistent with occasional migrations of the whale shark down to the bathypelagic zone besides daytime surface feeding habits. Our study portrays the diversity of visual opsin gene repertories among elasmobranchs and illustrates the potential of in vitro molecular experiments supported by genome sequencing, in understanding the visual ecology of deep-sea organisms.

Oscar Puebla, GEOMAR Helmholtz- Centre for Ocean Reserach Kiel; Pedro Martínez Arbizu, German Center for Marine Biodiversity Research (DZMB), SENCKENBERG am Meer

Studying the population genetics of deep-sea animals helps us understand their divergence, dispersal potential, as well as their ability to overcome natural barriers like oceanic trenches. Here, we report on a population genetic study of the deep sea ophiuroid Ophiacantha pacifica (Ophiuroidea: Ophiacanthidae) distributed across the Kuril-Kamchatka Trench (KKT) in Northwest Pacific. Using 2b-RAD sequencing, 7,877 genomewide single nucleotide polymorphisms (SNPs) were obtained from 36 individuals collected from six stations located on both sides of the trench. Previous haplotype network analyses based on the mitochondrial gene cox1 showed that only one of more than two dozen haplotypes was shared between sampling areas, indicating low genetic exchange across the trench. Nevertheless, when using SNP data, almost all individuals formed a single genetic cluster, with the exception of a few outliers−indicating that the KKT is no barrier to gene flow between the Sea of Okhotsk and the Northwest Pacific. The species seems to be under the influence of the East Kamchatka Current and several anticyclonic eddies, so although virtually nothing is known of the reproductive life history of O. pacifica, the genetic homogeneity shown here suggests that it likely includes a planktotrophic larval dispersal stage. In conclusion, the present study offered novel perspectives on the population connectivity of O. pacifica ophiuroids, revealing the potential interaction of ocean currents and geological barriers with reproductive adaptations in shaping genetic structure patterns in the Northwest Pacific.

Aplacophora is an ecologically important and phylogenetically significant clade of mostly deep-sea worm-shaped marine molluscs. Basic questions about aplacophoran biodiversity and evolution, such as the number of species, evolutionary relationships, and ancestral states of key characters remain unanswered. The number of aplacophoran taxonomists, which has always been small, has declined in recent years. Meanwhile, known but undescribed species and specimens collected in environmental surveys that remain unidentified continue to grow in number. Specimen identification often requires the labor-intensive process of histology, but newer technologies such as micro-CT scanning and DNA barcoding could significantly accelerate this process. I will present on a new project aimed at dramatically accelerating the pace of the study of aplacophoran biodiversity and systematics while training the next generation of invertebrate systematists. Specimen identification will employ a novel workflow combining stereo light microscopy, micro-CT, and SEM of whole specimens, DNA barcoding, and compound light microscopy of permanent sclerite mounts - all from the same animal. Goals of this project include identification of thousands of specimens, description of >50 new species, characterization of the faunas of particularly diverse and understudied regions, monographs for select taxa in need of revision, and production of a reference DNA barcode library. Further, the first aplacophoran genomes will be sequenced, enabling target-capture phylogenomics. A well-resolved and broadly sampled phylogenetic framework will make possible a revised classification that accurately reflects the group’s evolutionary history as well as ancestral state reconstruction of key traits for Aplacophora and Mollusca as a whole. Moreover, this integrative taxonomic workflow has applications on diverse other clades of understudied, deep-sea marine invertebrates.

Aggeliki Georgiopoulou, School of Environment and Technology, University of Brighton; Evan Edinger, Geography Department, Memorial University of Newfoundland; Katleen Robert, School of Ocean Technology, Fisheries and Marine Institute, Memorial University of Newfoundland

Seamounts, elevations greater than 1,000m, have been identified as biodiversity hotspots in numerous studies and are found throughout all five ocean basins. The Charlie-Gibbs Fracture Zone (CGFZ) is a prominent geological feature located along the Mid Atlantic Ridge (MAR), consisting of two parallel fractures, creating a highly variable seafloor bathymetry. It has been described as the most important latitudinal biodiversity transitional zone on the MAR but the faunal communities which live on the fracture zone have not been substantially documented or described. The Hecate seamount is on the CGFZ and has been officially designated as a Vulnerable Marine Ecosystem (VME), but there is limited knowledge of its biodiversity, with only a single trawl survey conducted back in 2004. The remotely operated vehicle (ROV) Holland I was utilised during the TOSCA (Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone) survey in 2018 to examine geological processes occurring at the CGFZ. The survey included 5 ROV video transects, with one spanning the Hecate seamount from the start point at 2,900m to its peak at 560m, a 2,340m ascent. The objective of the current study was to use this video footage to quantify the biodiversity of the Hecate seamount and determine which habitats provide the highest levels of biodiversity. Preliminary results show multiple FAO-recognised VME indicator species. These indicators include a coral garden (Octocorallia, n=238, Antipatharia, n=63), deep-sea sponge aggregation, mud- and sand-emergent fauna and tube-dwelling anemone patches. VME-indicators were observed on a range of substrates including mud flats, boulder fields and bedrock. Fishing nets observed in the ROV video on the seamount confirm that fishing efforts have affected the area and can have potentially devastating impacts on these vulnerable habitats, highlighting the importance of protecting this seamount into the future as it contributes to the biodiversity of the CGFZ.

Karen Croke, NUIG; Andrea Quattrini, National Museum of Natural History, Smithsonian, Invertebrate Zoology, Washington DC, USA; Claire Laguionie-Marchais, NUIG; Louise Allcock, NUIG

Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) are becoming increasingly prevalent in deep-sea research. This has resulted in more video footage of the deep sea being collected, concurrent with a decline in physical specimens recovered. As a result, identification of organisms is increasingly based on visual analysis of footage which may be subject to poor visibility and restricted views. The creation of ‘In-house’ guides by individual labs to analyse their own video data makes cross reference study between collections difficult. Our aim here is to compare visual identification of Alcyoniidae and Paramuricea with genetic data obtained from collected samples to enhance our guide on Irish deep-sea fauna. Video footage and genetic samples were obtained during 2017-18 as part of the Science Foundation of Ireland (SFI) project ‘Exploiting and conserving deep-sea genetic resources’. Collections took place in the Irish deep-sea area from Whittard Canyon and Porcupine Bank. Haplotype networks were constructed from mitochondrial mutS DNA sequences generated from collected samples. Morphology was compared from analysis of video footage as well as in situ photos. We obtained seven mutS haplotypes of Alcyoniidae versus six visual morphotypes. In some, but not all cases, the molecular haplotypes correspond to the morphotype, suggesting some groups can be discriminated visually. Morphological differences which can be used to distinguish among Alcyoniidae include number and shape of polyps, colour, overall size and the shape of holdfast. It is therefore possible to use information from the haplotype networks to correct our guide. For Paramuricea six haplotypes were produced compared with one morphotype. Visual discrimination between Paramuricea species is impossible and identification from images alone is limited to genus. Using genetic data will help establish the taxonomic level to which we can identify organisms based on videos and images.

Inmaculada Frutos, University of Lodz; Terue Kihara, INES Integrated Environmental Solutions; Maciej Studzian, University of Lodz; Łukasz Pułaski, University of Lodz; Polish Academy of Sciences; Magdalena Błazewicz, University of Lodz

Understanding the ecological and evolutionary processes that shape deep-sea diversity and distribution is vital to predicting likely faunal responses to human impacts. However, every biological analysis has to start with a robust species identification that enables comparison of diversity at different spatial and temporal scales. Yet, in notoriously under-sampled regions like the deep sea, many species are undescribed (>80%) and thus assessment of their diversity, origin and diversification remains fragmentary or unknown. Owing to low specimen number usually found in deep-sea samples puts constraints on assessing intra- vs. inter-specific variation. In the course of morphological examination, methods need to be optimised to receive sufficient information. Here we focus on two peracarid crustacean orders, isopods and tanaidaceans, among the most common and diverse deep-sea macrofaunal taxa, to evaluate the use of Confocal Laser Scanning Microscopy (CLSM) in deep-sea taxonomy. Both the exoskeleton and internal organs of crustaceans contain various strongly fluorescent pigments, some of them still chemically uncharacterised, yielding detailed, high contrast images of even very small morphological features of appendages, cuticle and tissues. Nonetheless additional staining with fluorescent dyes is beneficial enhancing signal to noise ratio and allowing uniform signal acquisition in well-defined fluorescence channels. A particular advantage of CLSM is that invaluable deep-sea material that contains only few specimens remains intact, while providing high-resolution visualization (as opposed to more widely used SEM) to delineate the species. In that way, CLSM has the potential to significantly enhance the quality of taxonomic descriptions and also to serve as a proxy or even as supplementary replacement for type material. The research has been financed by the Narodowa Agencja Wymiany Akademickiej (Poland) under the ULAM program (SK) and NCN 2018/31/B/NZ8/03198 (MB)

Tina Kutti, Institute of Marine Research in Norway, Bergen (IMR), Norway; Melissa Chierici, Institute of Marine Research in Norway, Bergen (IMR), Norway; Wolf-Christian Dullo, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany; Sascha Flögel, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany

Ocean acidification and warming are predicted to pose serious threats to cold-water corals (CWCs) within the next decade. Yet, little is known about the natural seasonal and short-term variability of ambient environmental conditions in CWC settings. This data is needed to create a baseline definition of modern temperature and carbonate chemistry conditions, which is vital for an accurate monitoring of warming and acidification trends and will furthermore help in elucidating the resilience of CWCs to climate change. Here, we provide continuous observational data of the hydrodynamic regime (recorded using two benthic landers) and point measurements of the carbonate- and nutrient systems, from five Lophelia pertusa CWC reefs in the Langenuen Fjord, southwestern Norway from 2016 to 2017. In this fjord setting we found similar mean biogeochemical conditions at all five reefs (composing three wall reefs and two bank reefs). These are in the range of that measured around other L. pertusa reefs in the northern Atlantic. However, the maximum and minimum values of the biogeochemical parameters measured differed between the five reefs, mainly driven by differences in the hydrodynamic regime. Over a tidal (<24 h) cycle, the variability of measured parameters at CWC depths was comparable to the intra-annual variability, demonstrating that single point measurements are not sufficient for documenting (and monitoring) the biogeochemical conditions in highly dynamic CWC sites. Due to seasonal and diurnal forcing, parts of the wall reefs experienced temperatures up to 4 °C warmer than the mean conditions (i.e. >12 °C) and high DIC concentrations of 20 µmol/kg over the suggested CWC threshold (i.e. >2170 µmol/kg) during some of our measured timepoints, indicating that shallow CWC reefs in fjords may act as an early hotspot for ocean warming and acidification and could forewarn us of the consequences of climate change on CWC diversity and function.

Ana Hilário, University of Aveiro; Louise Allcock, National University of Ireland Galway; David Bailey, University of Glasgow; Maria Baker, University of Southampton; Malcolm Clark, National Institute of Water and Atmospheric Research; Ana Colaço, Universidade dos Açores; Jon Copley, University of Southampton ; Erik Cordes, Temple University; Roberto Danovaro, Stazione Zoologica Anton Dohrn; Awantha Dissanayake, University of Gibraltar; Elva, Escobar, Universidad Nacional Autónoma de México; Patricia, Esquete, University of Aveiro; Austin, Gallagher, Beneath the Waves; Andrew, Gates, National Oceanography Centre; Sylvie, Gaudron, Université de Lille; Christopher, German, Woods Hole Oceanographic Institution; Kristina, Gjerde, IUCN Global Marine Program; Nicholas, Higgs, Cape Eleuthera Institute; Nadine, Le Bris, Sorbonne University; Lisa, Levin, Scripps Institution of Oceanography; Elisabetta, Manea, Institute of Marine Sciences Venice; Craig, McClain, Louisiana Universities Marine Consortium; Lenaick, Menot, Ifremer; Nelia, Mestre, Universidade do Algarve; Anna, Metaxas, Dalhousie University; Rosanna, Milligan, Halmos College of Natural Sciences and Oceanography; Agnes, Muthumbi, University of Nairobi; Bhavani, Narayanaswamy, Scottish Association for Marine Science; Sofia, Ramalho, University of Aveiro; Eva, Ramirez-Llodra, Norwegian Institute for Water Research / REV Ocean; Laura, Robson, The Joint Nature Conservation Committee; Alex, Rogers, REV Ocean; Javier, Sellanes, Universidad Católica del Norte; Julia, Sigwart, Senckenberg Research Institute; Kerry, Sink, South African National Biodiversity Institute; Paul, Snelgrove, Memorial University of Newfoundland; Paris, Stefanoudis, University of Oxford / Nekton Foundation; Paulo, Sumida, Universidade de São Paulo; Michelle, Taylor, University of Essex; Andrew, Thurber, Oregon State University; Rui, Vieira, Centre for Environment Fisheries & Aquaculture Science; Hiromi, Watanabe, Japan Agency for Marine-Earth Science and Technology; Lucy, Woodall, University of Oxford / Nekton Foundation; Joana, Xavier, University of Porto / University of Bergen

The health of the global ocean, on which society is dependent, is in decline. The importance of sustainable use to ocean health has long been recognized. The First World Ocean Assessment highlighted increasing ocean pressures from accelerated expansion of human activities affecting all ocean regions. In response to this concern, and in keeping with several international policy commitments, the UN General Assembly proclaimed 2021-2030 the Decade of Ocean Science for Sustainable Development. The Ocean Decade Roadmap recognizes the deep sea as a frontier of science and discovery, calling for research to advance understanding of deep-sea ecosystems. Published in March 2020, the draft Implementation Plan for the Ocean Decade describes a framework to guide the design and implementation of Actions throughout the Decade. These Actions underpin the move from the ‘ocean we have’ to the ‘ocean we want’. The draft plan calls upon the scientific community to develop Actions to help deliver on four key objectives. The Deep-Ocean Stewardship Initiative and the Scientific Committee on Oceanic Research have responded to this call through establishing working groups tasked with this development. In keeping with the Ocean Decade’s focus on fair and equitable partnerships, these groups gather experts from developed and developing nations, representing diverse ethnic backgrounds, different genders and career stages. Together, we propose a new Action, Challenger 150, a deep-sea biological science programme designed to deliver the capacity and knowledge to help achieve the desired state of the ocean at the end of the Decade. Here we provide a deep-sea context for the Ocean Decade’s four Objectives and outline how Challenger 150 will contribute. We urge the deep-sea community to engage with the programme as a shared endeavour; to forge regional and inclusive consortia, co-develop research bids aligned with the programme, and help achieve the Ocean Decade objectives.

Mercer Brugler, Division of Invertebrate Zoology, American Museum of Natural History, University of South Carolina; Andrea Quattrini, National Museum of Natural History, Smithsonian Institution; Peter Cowman, James Cook University; Tom Bridge, James Cook University, Queensland Museum; Dennis Opresko, National Museum of Natural History, Smithsonian Institution

The taxonomy and evolutionary history of black corals (Anthozoa: Antipatharia) are relatively unknown because they have few, varying, and sometimes overlapping morphological features, can occur deep (>8,000 m), and have scant and debated fossil records. Over the last 25 years, single-locus barcodes have been employed to bridge these knowledge gaps. However, slowly evolving and uninformative molecular markers have led to genera and species-level polytomies and general uncertainty regarding taxonomic boundaries. Genomic scale methods such as targeted enrichment can result in 100-1000s of nuclear loci for phylogenetic reconstruction and have proved useful in resolving long-standing taxonomic and evolutionary questions in anthozoan coral groups. Here, we test the utility of a baitset designed to target conserved element loci. We recovered a mean of 970 ± 260 SD loci per specimen. Phylogenomic reconstruction of a 75% complete alignment with representatives of all seven currently recognized families resulted in the first phylogenetic tree with high resolution and support at the generic and species level in black corals, eliminating polytomies that have previously confounded taxonomy. The phylogeny provides evidence for numerous amendments to the taxonomy at the family, genus and species-level. For example, our results suggest that Bathypathes patula consists of multiple undescribed species, the genus Alternatipathes is a junior synonym of Umbellapathes, and the family Aphanipathidae is polyphyletic, consisting of at least three distinct lineages. Lastly, using maximum likelihood methods for lineage age estimation, we investigate when and how deep and shallow water families diverged. These results highlight the effectiveness of target capture methods in resolving the taxonomy and evolutionary origins of difficult taxa. Future work to increase taxon sampling will help resolve the taxonomy of black corals and allow further investigation into their evolutionary history.

Robert Young, University of Southampton

Holothurians (sea-cucumbers) form a dominant part of the abyssal megafauna and are an important link between microbes and invertebrates within food-limited benthic habitats. Holothurian feeding activities may influence sediment microbial structure and distribution, benthic nutrient cycling and carbon processing. Despite their importance, the effect of holothurian bioturbating activity on benthic microbial communities is poorly understood. The gut microbiomes of six genera of holothurians with two distinct feeding strategies were examined from the North-East Atlantic, by using 16S rRNA gene amplicon sequencing and compared with sediment and water column samples. We found that microbial community composition and diversity varied with habitat type, gut compartment and holothurian feeding strategy. Taxa related to carbon and nitrogen fixation and cycling were highly abundant in the holothurian gut microbiomes. In particular, ammonia-oxidising Archaea (Thaumarchaeota) and non-photosynthetic Cyanobacteria (Melainabacteria) were more prevalent in gut microbiomes of subsurface deposit feeders. Both Thaumarchaeota and Melainabacteria were also observed in the ambient sediment, with the latter more abundant in the deeper sediment layers. Overall, the results indicate that gut microbes in holothurians may offer a nutritional advantage to the host by breaking down refractory organic matter in a food limited environment, especially for holothurians with a largely stationary lifestyle.

Jennifer A Dijkstra, University of New Hampshire Center for Coastal and Ocean Mapping

Species composition on low temperature ridge flank hydrothermal systems (RHFS) is unknown, yet important to understand due to the varying natural environmental conditions that surround venting and non-venting sites. This study uses thousands of images to examine community composition at venting and non-venting sites on Dorado outcrop and then couples images with collected environmental variables and bathymetric data. Dorado outcrop is an elongated 1 km x .5 km, 150-m tall discharge outcrop in 3100-m of water in the NE Pacific on the Cocos plate (9°N, 87°W). Unlike typical hydrothermal vents, waters discharging from venting sites on Dorado are slightly warmer (≤12°C) than ambient water temperatures. They are also oxygen deficient (≥54 µmol). The natural environmental variability on Dorado outcrop, therefore, make it an ideal study site to understand the drivers of community composition. Overall, eight phyla were observed: Annelida, Arthropoda, Chordata, Cnidaria, Echinodermata, Mollusca, Nematoda, and Porifera. Surprisingly, no significant differences in overall (mobile and sessile included) or with sessile only species composition was found between venting and non-venting sites. The most abundant family in venting and non-venting regions were Isididae (octocoral) and Brisingidae (sea star), respectively. Our results suggest that the variable environmental conditions associated with venting on low temperature RFHSs does not influence community composition.

Craig McClain, LUMCON ; Clifton Nunnally, LUMCON; River Bryant, ULL

Wood in the deep-sea serves as substantial food sources in an otherwise barren environment, forming specialized and diverse community assemblages and adding to diversity in the deep-sea. Little information is known of how wood fall community assemblages differ between wood types (species) and carbon availability. Forty three logs composed of eleven species and four distinct log masses (2, 4, 6, and 8 kg) were deployed in 2017 in the northern Gulf of Mexico along the continental slope at approximately 2,000 meters depth. Wood fall communities were analyzed after recovery in 2019 in efforts to identify the effects of wood type and carbon availability on Gulf of Mexico wood fall community assemblages. Three main conclusions can be drawn from this study: (1) Species abundance, richness, and diversity were found to increase with increasing wood mass in softwood communities; (2) species abundance, richness, and diversity were found to be highest in softwood when compared to hardwood, and (3) Gulf of Mexico wood fall community assemblages were found to be significantly more rich in species than wood fall communities off the coast of northern California. Our findings here suggest that natural variations in wood-falls, including wood type and size, may have a great impact on terrestrial carbon driven communities in the deep-sea.

Sarah Samadi, MNHN (Muséum National d’Histoire Naturelle), Paris, France ; Laure Corbari, MNHN; Tin-Yam CHAN, National Taiwan Ocean University, R.O.C., Institute of Marine Biology, Keelung, Taiwan ; Aurélien Arnaubec, Ifremer, Centre Méditerranée; Catherine Borremans, Ifremer; Karine Olu, Ifremer

Seamounts support biodiversity likely partly structured by habitat heterogeneity at various spatial scales. Few studies has considered the influence of substrate and microtopography on very fine scale by a quantitative approach. Locally, the 3D structure of habitat-forming species (corals, sponges) is also a factor of heterogeneity. Imagery use is growing in deep-sea community studies but megafauna identification is commonly assess by morphotypes that remains subjective. Taxonomic support by physical collect of specimens is often missing while many diagnostic characters cannot be seen on images. This is especially challenging for the identification of habitat-forming species that show high morphological plasticity and between species convergence. It is thus necessary to develop methodologies that consider these pitfall to assess benthic megafauna biodiversity robustly, and especially in areas with limited sampling such as the Mozambique Channel. We analysed image transects on several seamounts and island slopes in the Mozambique Channel. To assess the fine scale heterogeneity, we adapted a substrate size classification, and microtopography (10cm) were quantified from 3D mosaic reconstruction (Matisse3D SW). For the biodiversity characterization, our methodology is based on image annotation with BIIGLE software, allowing collaborative work with taxonomists and vouchers specimens collected on the same transects or area. This complementarity help to formalize image-based identification of fauna by providing better taxonomic support and to develop identification keys for target taxa. Finally, for corals and sponges, we propose a functional classification from morpho-functional traits observable or measurable on images. This allow to assess the role of habitat-forming species in shaping the community structure and their responses to abiotic constraints. Thesis co-funded by TOTAL and Ifremer as part of the Passive Margin Exploration Laboratories scientific project.

Emma Cavan, Imperial College London, UK; Kerrie Swadling, Institute for Marine and Antarctic Studies, Australia; Diana Davies, CSIRO, Australia; Tom Trull, CSIRO, Australia; Philip Boyd, Institute for Marine and Antarctic Studies, Australia

Our understanding of intra- and interannual variability in the deep Southern Ocean ecosystem is hampered by logistical constraints that come with working in this remote region of the planet. One solution for this problem is automated moorings; for example, at the Southern Ocean Time Series site (SOTS) at 47˚S in the subantarctic. Sediment traps have been deployed at the mooring site since 1998, located at different depths below the mesopelagic zone (1000, 2000 and 3800 m water depth) to measure the variability in sinking organic carbon flux. These devices also collect “swimmers”; live zooplankton swim into the traps and are killed by preservative but are subsequently separated from the smaller size fraction of passively sinking particles. Zooplankton play an important role in the food web as they transfer energy from phytoplankton to higher trophic levels including fish and marine mammals. Due to their short life span, they are sensitive to environmental change and used as an indicator of the structure and health of the Southern Ocean ecosystem. Here, we will present a look at this zooplankton time-series with a focus on the main groups, i.e. copepods, amphipods, pteropods, chaetognaths and ostracods in relation to carbon flux and environmental drivers such as temperature. With this important time series, we can increase our understanding of seasonal and inter-annual variability of plankton composition and identify environmental drivers responsible for community shifts. Finally, we can predict future changes in ecosystem functioning that can inform conservation and management decisions in the subantarctic Southern Ocean.

Oliver S. Ashford, Scripps Institution of Oceanography/University of California San Diego; Wânia Duleba, School of Arts, Science and Humanities/University of São Paulo; Lisa A. Levin, Scripps Institution of Oceanography/UC San Diego

Methane seepage creates gradients in food availability and sulfide stress within continental margin sediments. The influence of seepage on the density, composition and vertical distribution of meiofauna (> 42 µm) was investigated for sediments collected in 2017 at Mound 12 (~1000 m) on the Costa Rican Pacific margin. 8,216 metazoan individuals were sorted from the upper 3 cm of 10 cores from actively seeping (4), transition (4) and background (2) habitats. Approximately 40% of the metazoans were found both in the 0-1 and 1-2 cm, 20% in the 2-3 cm fractions, but this meiofauna in active sites were concentrated in the uppermost fraction (~86%). Transition sites exhibited highest metazoan densities (470.39 ± 416.17 ind/cm2), with a more homogeneous vertical distribution. Nematoda was the dominant meiofaunal taxon, comprising ~65% in the active sites, 80% in transition and ~92% in the background sites. Other permanent meiofaunal taxa (Copepoda, Ostracoda, Kinorhyncha) presented higher densities in the transition sites. Meiofaunal polychaetes, bivalves, and gastropods were more abundant in the active sites. Macrofauna (> 300 µm) collected from the same cores exhibit density patterns similar to the metazoan meiofauna, possibly generated by lesser sulfide toxicity at the transition than active seep and lesser predation than in the background sediments. As for the foraminiferans, thanatocenosis (death assemblage) comprised 98% of the total, concentrated in active sites (~83%). Biocenosis (living calcareous, agglutinated and organic-shelled ‘monothalamic’ foraminifera) contributions were slightly higher and more evenly distributed throughout the sediment profile in transition sites, with densities of 18.34 ± 6.37 ind/10cm3 and presenting its higher density in the background sites (23.47 ± 5.06 ind/10cm3).

Most species living in the deep sea have not been sampled and remain undiscovered. This is especially true for Australia where taxonomic research lags behind that of other developed countries. A lack of taxonomic information presents a major challenge for mapping biodiversity, species distribution and connectivity, information which is critical for managing and protecting the unique deep-sea environment. A pioneering 2017 expedition on RV Investigator sampled the Australian eastern lower bathyal and abyssal environments from Tasmania to southern Queensland including Marine Parks. A total of about 6000 annelid specimens (Polychaeta, Sipuncula and Echiura) were collected. All specimens were registered at museums and then sent to 23 annelid taxonomists around the world. Over 200 species were recorded, 81 of which may be new to science. Species lists were combined into an annotated and illustrated checklist of all annelids collected from the cruise. This work reports critical baseline knowledge about benthic invertebrates from a previously unknown abyssal region of the world’s ocean. We emphasise the importance of lodging voucher specimens and of taxonomic names in and environment where the majority of species have no name.

Michelle L. Taylor, University of Essex

Investigating population structure in non-model-organisms is becoming increasingly common using next generation sequencing (NGS) techniques. Different NGS techniques require specific outputs from DNA extractions to perform as desired and meet individual research needs: ample DNA yield, provide high molecular weight (HMW) DNA, to be time-cost effective, and increasingly considered- minimal plastic waste usage. Here we compare five DNA extraction methods: a phenol-based extraction, salting-out protocol, and three commercially available kits from Qiagen: Blood and Tissue, Plant Mini, and PowerSoil Pro. These protocols were tested across non-model organisms: deep-sea octocorals and scleractinians. We included four individuals from each of the octocorals: Acanella arbuscula, Paragoria sp., and Pennatula sp. as well as four individuals from each of the scleractinian corals: Madrepora oculata, Lophelia pertusa, and Desmophyllum dianthus. DNA yield, purity, ratio of high to low molecular weight DNA, time and cost, and plastic waste produced were measured and compared across methods. The Qiagen Plant Mini kit produced the highest ratio of HMW DNA to degraded DNA in all corals tested. Kit DNA extractions used significantly more plastics than non-kit protocols. Time-cost analyses found that the salting-out protocol was most cost effective. Overall for NGS methods requiring “clean” HMW DNA, if cost and plastic waste are not a concern, the Plant Mini kit is suggested; however, the salting-out method is a good alternative taking into account: yield, HMW to degraded DNA ratios, cost (lowest), and plastic use (lowest). For NGS methods requiring the most DNA yield possible regardless of HMW needs, the phenol-based extraction used here is suggested.

Ashley Rowden, Victoria University of Wellington; National Institute of Water and Atmospheric Research; David Bowden, National Institute of Water and Atmospheric Research; Malcolm Clark, National Institute of Water and Atmospheric Research

Seamounts are a significant source of habitat for deep-sea benthic communities, providing fauna with access to hard substrata and shallower water masses compared to surrounding sedimentary plains. Additionally, productivity near seamounts can be enhanced by interactions between seamount topography and the water column. Within a single seamount, the uneven distribution of reliefs and physical structures produces a mosaic of various habitat patches and current regimes, which can contribute to high intra-seamount variability in megabenthic community structure. To investigate potential drivers of community variability within a seamount, analyses must therefore be conducted at a fine spatial scale (several-10s metres). To do so, we analysed data from two deep seamounts, located on the central northern and eastward flanks of Chatham Rise, a plateau which extends for ~1000 km east from New Zealand. Using data from two seamounts of differing sizes, depth ranges, and locations of Chatham Rise enabled us to examine both intra- and inter-seamount variability in megabenthic community structure. Each seamount was surveyed with NIWA’s underwater towed camera to collect imagery and video. Transects were conducted from the peak of each seamount to its base along the cardinal directions, and images were taken at 15s intervals. Every image from four select transects of each seamount was annotated using the online image annotation tool BIIGLE 2.0 to quantify substrate composition and taxon abundance. These data were combined with other environmental variables obtained from multibeam bathymetry data (ruggedness, slope, depth, seafloor aspect and curvature) and analysed with multivariate statistical routines to examine the correlation between habitat and environmental variables with community structure; these results will be presented. This analysis is part of an ongoing study using a modelling approach to predict the resilience of benthic communities on New Zealand seamounts.

Paul Yancey, Whitman College, Walla Walla, WA, USA; Olga Tikhonova, Institute of Biomedical Chemistry, Moscow, Russia; Nikita Vavilov, Institute of Biomedical Chemistry, Moscow, Russia; Victor Zgoda, Institute of Biomedical Chemistry, Moscow, Russia; Dmitri Davydov, Washington State University, Pullman

We explore the principles of pressure tolerance in enzymes of deep-sea ﬁshes using lactate dehydrogenases (LDH) as a case study. We compared the effects of pressure on the activities of LDH from hadal snailﬁshes Notoliparis kermadecensis and Pseudoliparis swirei with those from a shallow-adapted Liparis ﬂorae and an abyssal grenadier Coryphaenoides armatus. We then quantiﬁed the LDH content in muscle homogenates using mass-spectrometric determination of the LDH-speciﬁc conserved peptide LNLVQR. Existing theory suggests that adaptation to high pressure requires a decrease in volume changes in enzymatic catalysis. Accordingly, evolved pressure tolerance must be accompanied with an important reduction in the volume change associated with pressure-promoted alteration of enzymatic activity (dVpp). Our results suggest an important revision to this paradigm. Here, we describe an opposite effect of pressure adaptation—a substantial increase in the absolute value of dVpp in deep-living species compared to shallow-water counterparts. With this change, the enzyme activities in abyssal and hadal species do not substantially decrease their activity with pressure increasing up to 100–200 MPa, well beyond full-ocean depth pressures. In contrast, the activity of the enzyme from the tidepool snailﬁsh, L. ﬂorae, decreases nearly linearly from 1 to 250 MPa. The increased tolerance of LDH activity to pressure comes at the expense of decreased catalytic efﬁciency, which is compensated with increased enzyme contents in high-pressure-adapted species.The newly discovered strategy is presumably used when the enzyme mechanism involves the formation of potentially unstable excited transient states associated with substantial changes in enzyme-solvent interactions.

Sebastian Hennige, University of Edinburgh

The ecosystem services provided by coral reefs are worth over $100 billion annually and include coastline protection, tourism, food and medical derivatives. However, the health of the constituent corals can be significantly impacted by climate change. The proliferation of corals is reliant upon optimal light and current conditions. The ‘Goldilocks Zone’, where conditions are ‘just right’ will promote coral growth compared to sub-optimal zones. By creating a 3D Computational Fluid Dynamics (CFD) model to understand coral growth in ‘optimal conditions’ it is possible to simulate a variety of different future environments. Such a model could be a powerful tool for coral reef management. Ocean acidification is a major threat to cold-water coral reefs as the ever shallowing aragonite saturation horizon could leave up to 70% of cold-water corals in aragonite under-saturated zones by 2100. In these more acidic ocean conditions, the net cold-water coral growth becomes more difficult, as the cold-water coral skeletons can be dissolved in under-saturated water. This dissolution will affect dead coral framework and may lead to a net loss of reef accretion. Modelling the mechanisms behind coral skeleton dissolution in various acidification scenarios is a helpful way to visualize the effect of ocean acidification to cold-water coral reefs and can help determine reef recovery times under various scenarios. The Smoothed Particle Hydrodynamics (SPH) method is used for the models as its mesh-free Lagrangian nature is ideal for simulations where the examined object (i.e. a coral) is growing dynamically. SPH can readily simulate free-surface boundaries and turbulent environments, while it is essentially ‘3D ready’. The SPH solver is written using the C++ programming language and is parallelized with the Open Multi-Processing (OpenMP) application programming interface to allow for time-effective high-resolution simulations. 

Sergi Taboada, Natural History Museum UK, Universidad Autónoma de Madrid & Universidad de Alcalá Spain ; Ana Riesgo, Natural History Museum UK; Cristina Díez-Vives, Natural History Museum UK; Fabio C. De Leo, Ocean Networks Canada & University of Victoria, Canada; Rachel M. Jeffreys, University of Liverpool UK; Jonathan T. Copley, University of Southampton UK; Crispin T. S. Little, University of Leeds & Natural History Museum, UK; Pilar Ríos, Instituto Español de Oceanografía, Spain; Javier Cristobo, Universidad de Alcalá & Instituto Español de Oceanografía, Spain; Jon T. Hestetun, Norwegian Research Centre (NORCE), Norway; Adrian G., Glover, Natural History Museum UK

The peripheral areas of deep-sea hydrothermal vents are often inhabited by an assemblage of animals distinct to those living close to vent chimneys. For many such taxa, it is considered that peak abundances in the vent periphery relate to the availability of hard substrate as well as the increased concentrations of organic matter generated at vents, compared to background areas. However, the peripheries of vents are less well-studied than the assemblages of vent-endemic taxa, and the mechanisms through which peripheral fauna may benefit from vent environments are generally unknown. Understanding this is crucial for evaluating the sphere of influence of hydrothermal vents and managing the impacts of future human activity within these environments, as well as offering insights into the processes of metazoan adaptation to vents. In this study, we explored the evolutionary histories, microbiomes and nutritional sources of two distantly-related sponge types living at the periphery of active hydrothermal vents in two different geological settings (Cladorhiza from the E2 vent site on the East Scotia Ridge, Southern Ocean, and Spinularia from the Endeavour vent site on the Juan de Fuca Ridge, North-East Pacific) to examine their relationship to nearby venting. Our results uncovered a close sister relationship between the majority of our E2 Cladorhiza specimens and the species Cladorhiza methanophila, known to harbour and obtain nutrition from methanotrophic symbionts at cold seeps. Our microbiome analyses demonstrated that both E2 Cladorhiza and Endeavour Spinularia sp. are associated with putative chemosynthetic Gammaproteobacteria, including Thioglobaceae (present in both sponge types) and Methylomonaceae (present in Spinularia sp.). These bacteria are closely related to chemoautotrophic symbionts of bathymodiolin mussels. Both vent-peripheral sponges demonstrate carbon and nitrogen isotopic signatures consistent with contributions to nutrition from chemosynthesis.

James Lunden, Department of Biology, Temple University; Alexandria Rhoads, University of Rhode Island; Andrew Davies, University of Rhode Island; Erik Cordes, Temple University

Coral reefs support key ecosystem processes and harbor an abundant and diverse fauna, yet their ecological niche and distribution on the deep (> 200 m) seafloor remain poorly understood. Recent mapping expeditions and submersible dives on the the U.S. Atlantic margin have confirmed the presence of numerous coral mounds and linear reef structures that were not detected in coarser-resolution surveys. Previous predictive habitat models for scleractinians placed a low probability of corals in much of this area. Here, we use these newly acquired bathymetry and coral distribution data to create predictive habitat models both for the presence and abundance (% cover) of Lophelia pertusa, the primary reef-forming species. In addition, the distribution of coral mounds in two different regions was estimated using a pixel-based, semi-automated classification method. Our results suggest that large swaths of seafloor surrounding the new observations that are likely to support scleractinians. We also test the validity of the model by projecting it onto two sites surveyed on subsequent ROV dives and assessing model performance in predicting L. pertusa presence and abundance. Notably, these areas are outside of the Mid-Atlantic Fisheries Management Council Deep-Sea Coral Habitat Areas of Particular Concern (HAPC) and may represent climate refugia for reef-building corals due to their location eastward of the main axis of the Gulf Stream. We test this climate refugia hypothesis using data from multiple climate change scenarios. These models represent an extension of the realized niche of this species, and may aid in conservation and exploration efforts through prediction of other of L. pertusa presence, abundance, and climate refugia.

Patricia Esquete, CESAM (Center of Environmental and Marine Studies), Universidade de Aveiro; Marina Cunha, CESAM.

The Tanaidacea are ubiquitous and amongst the most abundant taxa in the deep sea. However, their diversity in submarine canyons, remains largely unknown. Here, two new tanaidomorph tanaidaceans, belonging to the genera Paranarthrura and Paranarthrurella are formally described. Paranarthrura cousteaui sp. nov. is distinguished for the combination of the following characters: uropod endopod bi-articulated; uropod exopod shorter than first endopod article, presence of one penicillate seta in the basis of pereopods 4-6, one seta in the maxilliped endite, and one long midventral seta in cheliped. This species was found at the upper reaches of three Portuguese canyons Cascais, Setúbal and Nazaré Canyons and adjacent open slope, between 897 and 1001 m water depths. Paranarthrurella flamenco sp.nov. has been included in this genus, for which the diagnosis has been modified. It can be differentiated from the other Paranarthurella species by the presence of pleopods, presence of a dorsodistal spine in the antenna article-2, uropod endopod article-1 clearly shorter than article-2, absence of hyposphaenium and pleotelson apex directed downwards. This species was found at the middle reaches of Setúbal Canyon (3214-3219 m water depth).

Hiroshi Yamasaki, Kyushu University; Taeko Kimura, Mie University; Susumu Ohtsuka, Hiroshima University; Reinhardt M. Kristensen, University of Copenhagen

Loricifera is a metazoan phylum characterised by its introvert and neck bearing numerous scalids, and sclerotized abdomen with longitudinal subdivisions. It is exclusively found in marine sediments from shallow waters to the deep-sea. So far, 38 species have been described and many more undescribed new species are known from published and unpublished literature. More than half of the described species are known from depths deeper than 200 m. The undescribed genus and species we report was collected from several sites in the Sea of Kumano (water depth ranging from 321 m to 1,059 m) and Yaku-Shin-Sone bank (177 m deep), Northwest Pacific, during the research cruises of TR/V Toyoshiomaru and T/V Seisuimaru. The undescribed genus and species’ numerous longitudinal folds in the adult lorica and the internal armature and mucrone-free toes of the Higgins larva indicate its membership in the family Pliciloricidae. However, its morphology distinguishes it from the three described pliciloricid genera as follows: the adult has a long, rigid mouth tube with a membrane-like umbrella extruded from the mouth opening and 15 single trichoscalids and the Higgins larva with clavoscalids having ventral, sub-terminal swelling, scalids of second row as a short, simple spine, no clearly delimited collar, thorax with numerous folds, two pairs of posterior setae, and slender toes. Further, we conducted morphological comparison of our undescribed genus and species to previously reported deep-sea taxa not formally described, in an attempt to integrate these information in a more reliable context.

Peter Etnoyer, NOAA National Centers for Coastal Ocean Sciences; Andrea Quattrini, Smithsonian Institution, National Museum of Natural History; Thomas Greig, NOAA National Centers for Coastal Ocean Sciences

Following the catastrophic Deepwater Horizon Oil spill in the Gulf of Mexico (GoMx) in 2010, surveys of mesophotic reefs in the Pinnacles Trend region revealed significant injury to about one-third of large gorgonian octocorals. Plans to restore these reefs require a better understanding of their genetic diversity and distribution. To support a larger population connectivity study of impacted octocorals in the GoMx, this study combined sequences of mitochondrial marker mutS and nuclear 28S rDNA to confirm the identity of Swiftia sea fans in the Gulf of Mexico and examined the phylogeny of the genus. Our data show that Swiftia exserta is very distinct from other Swiftia sequences at both gene regions. In addition, we provide strong evidence of Swiftia polyphyly, suggesting major revision of the genus is warranted. This information enhances our understanding of the geographical distribution of the impacted corals and will help guide management and restoration efforts in the northwestern Gulf of Mexico.

Brian Bett, National Oceanography Centre; Emily Mitchell, University of Cambridge Dept of Zoology; Henry Ruhl, MBARI / National Oceanography Centre

Spatial heterogeneity in the benthic environment affects the diversity and distribution of organisms, and ecosystem function. While large-scale bathymetric variation has been studied on abyssal plains, mesoscale community variation has been overlooked. We investigated the role of mesoscale variation in the structure and function of abyssal megafaunal assemblages across modest bathymetric variation (~10 m water depth intervals) on an abyssal hill, and horizontal variation at the 0.1 – 10 km scale across three areas at the Porcupine Abyssal Plain. We used seabed photographs captured with an autonomous underwater vehicle and sediment cores to assess the sedimentary habitat and megafaunal ecology. Sediment particle size and organic carbon content varied significantly with bathymetric variation. The density, biomass, diversity, and composition of megafaunal communities were significantly different between ~10 m depth intervals, and also between spatial areas. Notably, megabenthic communities were significantly different in two plain areas with no differences in sediment characteristics and only a 2 m difference in water depth. We also quantified spatial distributions and conducted a network analysis of associations in the communities in the three areas. We found non-random intraspecific distributions of most morphotypes in all areas. Organisms on the abyssal plain had high connectance, while the network on an abyssal hill was highly dependent on one morphotype. The reduced connectance of the hill community suggests that it is potentially more vulnerable to perturbation than those on the plain. Interspecific associations on the abyssal plain occurred across broad taxonomic groupings, likely related to sedimentary habitat needs and competition for detrital resource. These observations indicate that abyssal mesoscale heterogeneity has been greatly underestimated, with implications for the appropriate design and interpretation of abyssal survey and monitoring programmes.

Jorge León, Anadarko Colombia Company; Vladimir Puentes, Anadarko Colombia Company; Santiago Herrera, Department of Biological Sciences, Lehigh University

Methane-seep chemosynthetic communities are found in patchy areas where methane and other hydrocarbons leak through the seafloor. Although relatively common in continental margins, chemosynthetic communities in the Caribbean region are poorly known. Their existence in Colombian waters has been suggested by the presence of carbonates and specimens belonging to seep-endemic species obtained through trawling surveys, and some indicative information from seismic, geothermal, and multi-beam data. Predictive habitat models incorporating bathymetry and backscatter data have also indicated the presence of hard ground areas (presumably authigenic carbonates formed due to chemosynthetic activity), which are consistent with water column plume anomalies. Here, we further validate the predictions of these models, and present the first visual characterization of methane seep communities in the Colombian Caribbean using seafloor images taken with a towed camera system and samples collected through piston coring. The results demonstrate that the habitat predictive model reliably predicts the location of seep habitats, however it may overestimate the habitat areas. Chemosynthetic communities at these sites resemble those ones found off Trinidad and Tobago and the Gulf of Mexico. Dominant species include tubeworms (Lamellabranchia sp. and Escarpia sp.), mussels (Bathymodiolus sp.), shrimp (Alvinocaris sp.), and squat lobsters (Munidopsis sp.). These results represent foundational knowledge of Colombian deep-sea ecosystems. This research also represents the starting point for the understanding of the patterns and processes that have shaped biodiversity in the deep waters of the Southern Caribbean.

Tammy Norgard, Fisheries and Oceans Canada

In recent years, Fisheries and Oceans Canada scientists and partners have documented evidence of rapid changes in the deep ocean of the Northeast Pacific—changes that threaten life in what should be remarkably stable environments. Deep ocean chemistry is changing. The region is losing oxygen (15% since 1960), and calcium carbonate saturation horizons are shoaling at 1-2 m/year. Deep seafloor ecosystems are changing. Ghost fishing, habitat destruction, and other impacts of historical fishing continue for decades or longer. Species distributions are changing. Tropical “jelly blooms” at high latitudes alter deep ocean nutrient flux. Each environmental change has cascading ecological implications. These findings warrant moving beyond the precautionary approach towards plans that support and build resilience for future large-scale declines in ocean ecosystem health. Mitigating direct human impacts will be vital as deep ocean species continue to suffer environmental changes that are beyond our immediate control. The Canadian Government and coastal First Nations are working to safeguard the biological diversity in deep ocean ecosystems within new and pre-existing Marine Protected Areas in the Northeast Pacific.

Helena Wiklund, Natural History Museum London; Muriel Rabone, Natural History Museum London; Magdalena Georgieva, Natural History Museum London; Thomas Dahlgren, University of Gothenburg; Adrian Glover, Natural History Museum London

The Clarion Clipperton Zone (CCZ) is a vast region of abyssal seafloor situated in the central Pacific ocean that has been the subject of intense seabed mining exploration for polymetallic nodules in recent decades. Documenting and understanding the biodiversity and ecology of the CCZ will be integral to understanding the potential impacts of mining in this region. In this poster, we present a new species of abyssal annelid (Nereididae; Neanthes) described from the CCZ – a relatively large animal found living both inside polymetallic nodules and in xenophyophores (giant foraminifera) growing on nodules, highlighting the importance of the mineral resource itself as a distinct microhabitat. Widespread, abundant, charismatic, and easily recognisable, this new Neanthes species is also considered to be a suitable candidate for further assessments of biogeography and population connectivity patterns in the region, and as a potential indicator taxon for future monitoring of the impacts of seabed mining.

David Barnes, British Antarctic Survey; Saul Cunningham, Australian National University; Bruce Doran, Australian National University

Sponges are key long-living components of deep polar seafloor habitats, often supporting thousands of individual seabed animals and performing important nutrient-cycling functions. In order to support numerous and varied research and management needs in the current and near future, good quality taxonomic, temporal and spatial data is vital. The implications of quality impact our ability to monitor and model impacts to deep-sea sponge communities, decision-making in relation to the management and conservation of vulnerable deep-sea habitats, and limit our ability to assess deep-sea ocean health. Over 60,000 polar sponge data records have been assessed using newly developed quality control and completeness of sponge distribution records provided by OBIS (Ocean Biogeographic Information System). This assessment evaluates the current variability in quality of sponge data across polar oceans, including taxonomic, spatial, and temporal resolution; the quality of information in protected regions; and regions that are currently or in the future, predicted to be undergoing rapid human-mediated and/or climatic changes. Strengths and weaknesses of current sponge data are highlighted. Emphasis is placed on the important future implications of the quality of spatial, temporal and taxonomic information on deep-sea polar sponges for understanding impacts and improving management.

Mackenzie Gerringer, State University of New York Geneseo ; Michael Coronado, Whitman College; Paul Yancey, Whitman College

Atmospheric CO2 levels are increasing, causing major climatic changes that affect ecosystems across the planet. In the ocean, increasing temperatures result in less dissolved oxygen. While thermohaline circulation keeps most of the deep sea well-ventilated, expanding oxygen minimum zones increasingly threaten deep-sea species. Although research in this area has advanced, much remains unknown about how deep-sea species will respond to changing oxygen levels, especially in deeper waters. Here, we investigate hemoglobin (Hb) in deep-sea fishes as a metabolic and environmental bioindicator to understand the impacts of declining oxygen levels in the deepest ocean zones. We analyzed blood from deep-sea fishes from the Marina and Kermadec trenches and abyssal plains, with specimens from families Zoarcidae (eelpouts), Ophidiidae (cusk eels), Macrouridae (rattails), and Liparidae (snailfishes), with a collection depth range of 1,554-7,626 meters. These dominant fish families in the abyssal and hadal zones serve as strong test systems for understanding metabolism in deep-sea fishes. We found that Hb content was higher in locations with lower oxygen levels (p <0.05, n = 18). Presumably more Hb allows greater uptake of oxygen from hypoxic surroundings, and could potentially be upregulated. We also found that in species with lower Hb levels, anaerobic enzyme activity was higher than aerobic activity. Less Hb indicates less oxygen intake, which might mean that these species rely more heavily on anaerobic respiration than aerobic respiration. Spectrunculus grandis did not conform to this trend. This cusk eel has high water content in its muscles, subdermal gelatinous tissues, and a relatively lethargic lifestyle. These data simultaneously inform us about the conditions of the environment these species inhabit and their individual metabolic functions and role in the deep-sea ecosystem.

Katrin Linse, British Antarctic Survey; Huw Griffiths, British Antarctic Survey; Christian Haas, Alfred Wegener Institute for Polar and Marine Research; Hanieh Saeedi, Senckenberg Research Institute and Natural History Museum; Angelika Brandt, Senckenberg Research Institute and Natural History Museum

The RRS James Clark Ross and the RV Polarstern carried out expeditions in the Atlantic sector of the Southern Ocean (SO) and in the Weddell Sea, sampling peracarid crustaceans using an epibenthic sledge (EBS). The expeditions sampled three different areas characterised by different regimes of ice coverage (the ice free South Orkney Islands, the East Antarctic Peninsula including the Prince Gustav Channel which ice shelf collapsed in 1995 and the seasonally ice-covered Filchner Trough Filchner Trough). The aim of the study was to assess the influence of ice coverage on peracarid composition and abundance. Besides, the influence of other environmental parameters (including chlorophyll-a and phytoplankton concentrations, depth, temperature, salinity, sediment type, current velocity, oxygen, iron, nitrate, silicate and phosphate) was also investigated. A total of 64766 peracarids were sorted and identified at order level (Amphipoda, Isopoda, Cumacea, Tanaidacea and Mysidacea). The calculated trawling distances were normalised to 1000 m hauls in order to carry out comparative analyses. Amphipods were the most abundant group representing the 32% of the total abundances, followed by Cumacea (31%), Isopoda (29%), Mysidacea (4%), and Tanaidacea (4%). Statistical analysis showed a significant correlation between the total abundance of peracarids from different areas and environmental parameters such as chlorophyll concentration, depth, ice coverage, salinity and temperature. In particular, higher values of chlorophyll and ice coverage result in an increase of peracarid abundance. Our study shows the interaction between environmental parameters and macrobenthic peracarids providing us useful information on how possible changes of such parameters could have an influence on their actual distribution and abundance. A better understanding of the aforementioned interactions can be an important factor to predict the ecological impact induced by the on-going climate change.

Heather Bracken-Grissom, Florida International University

Diel vertical migration of deep-sea animals represents the largest migration on our planet. Vertically migrating fauna are subjected to a variety of light fields among other environmental conditions that can have notable impacts on sensory mechanisms, including an organism’s visual capabilities. Among deep-sea migrators are oplophorid shrimp, that vertically migrate 100s of meters (m) to feed in shallow waters at night. These species also have bioluminescent light organs called photophores that emit light during shallow-water migrations to aid in a dynamic form of camouflage known as counterillumination. The organs have recently been shown to contain opsins and other genes that infer light sensitivity. Knowledge regarding the impacts of this vertical migratory behavior, and fluctuating environmental conditions, on sensory system (visual/photophore) evolution is unknown. In this study, the oplophorid Systellaspis debilis was either collected pre-sunset (Day) from 450-750 m, or pre-dawn (Night) from 150-330 m to ensure sampling across the vertical distributional range. RNA was then extracted and sequenced from the light sensitive tissues (eyes/photophores). De novo transcriptomes were assembled discretely for each tissue from Day (n=5) and Night (n=5) specimens and analyzed to characterize opsin diversity, visual and light interaction genes within a phylogenetic context. Gene expression analyses were also conducted to quantify expression differences associated with the migration. This study sheds light on the visual system of a deep-sea bioluminescent shrimp and provides additional evidence for photophore light sensitivity. Our findings also suggest opsin coexpression and subsequent fluctuations in opsin expression may play an important role in diversifying the visual responses of this deep-sea vertical migrator.

Anna Metaxas, Dalhousie University

Deep-water corals, including sea pens, provide nursery and feeding areas, and increase habitat complexity. Deep-water corals have been identified as indicator species of vulnerable marine ecosystems, because of their lifestyles and exposure to threats such as bottom contact resource extraction activities. We compared deep-sea tools (remotely operate vehicle, drop camera, and research trawl) used to quantify epibenthic megafauna at two stations in the Laurentian Channel Marine Protected Area, eastern Canada. Data from the cameras of the remotely operated vehicle are augmented with advanced positioning, sampling, and metadata allowing for a wider range of analyses, with least disturbance and most real-time control. Imagery tools (both remotely operated vehicle and drop camera) captured sessile epifauna and recruits, and provided locations for abundance, making further examination of spatial structure and species associations possible. The drop camera better captured taxon-specific abundance and diversity at one but not both stations. Data from trawls can provide biomass and size estimates for taxa with greater coverage, but was not efficient for sea pens, and cannot elucidate fine-scale distribution (< 0.75 nautical miles). Overall, this research will be applicable to other deep-sea ecosystems globally and inform a monitoring framework for deep-sea Marine Protected Areas.

Tanja Stratmann, Utrecht University; Lidia Lins, Ghent University; Ann Vanreusel, Ghent University; Autun Purser, Alfred Wegener Institute; Yann Marcon, University of Bremen; Clara Rodrigues, Universidade de Aveiro; Ascensão Ravara, Universidade de Aveiro; Patricia Esquete, Universidade de Aveiro; Marina Cunha, Universidade de Aveiro; Erik Simon-Lledó, National Oceanography Centre Southampton; Peter, van Breugel, NIOZ Royal Netherlands Institute for Sea Research; Andrew K., Sweetman, Heriot-Watt University; Karline, Soetaert, NIOZ Royal Netherlands Institute for Sea Research; Johan, van de Koppel, NIOZ Royal Netherlands Institute for Sea Research; Peter C., de Ruiter, University of Amsterdam; Dick, van Oevelen, NIOZ Royal Netherlands Institute for Sea Research

Deep-sea ecosystems are under increasing anthropogenic pressure, sparking research into sustainable usage of our ocean’s natural resources. Disturbance studies, using both naturally occurring stressors and experimental stressors, are employed to understand the effects of different types of disturbances, and results are extrapolated to predict how future ocean conditions might impact deep-sea ecosystems. In this talk I want to demonstrate how in situ observations can be combined with energy-flux food-web modeling to study both ecosystem functioning and ecosystem stability. Our benthic food-web model of the ‘DISturbance and reCOLonization’ (DISCOL) experiment in the Peru Basin showed that, 26 years after the initial sediment disturbance, abyssal ecosystem functioning measured as total system C throughput was still significantly reduced by 15%, mostly due to significant reduction (35%) of microbial C cycling. Furthermore, I will present preliminary results of recovery time and ecosystem stability of a submarine canyon system as inferred from a previously published energy-flux food-web model with the new R-package ‘fwstability’. Integration of in situ observations into food web models can help us understand ecosystem wide effects of disturbances to make better informed choices regarding natural resource exploitation.

Elizabeth Hetherington, UCSD; Anela Choy, UCSD; Steven Haddock, MBARI; Casey Dunn, Yale University

Siphonophores are abundant and diverse predators in the Offshore Central California Current (OCCC) ecosystem. Due to limited access to the deep midwater environment, little is known about the diets of most deep-dwelling species. Early work on siphonophore diets relied on visual gut content inspection, which can rarely detect and identify soft-bodied prey which does not leave recognizable parts behind. Observation-based studies using Remotely Operated Vehicles (ROVs) overcome this issue and placed siphonophores in an important mid-trophic position, consuming crustaceans, fish, and jellyfish. However, ROV-based methods are unable to detect small prey (such as copepods, ostracods, and larval fish) whose capture cannot be easily observed through video recordings. Recently, DNA metabarcoding in other marine predators have revealed the importance of prey taxa that were overlooked by traditional methods. Moreover, metabarcoding can detect prey that was ingested hours before specimen collection from traces of DNA released during digestion and thus is better suited for the study of deep-sea species with long intervals between prey captures. In this study, we perform DNA metabarcoding of the gut contents of 27 siphonophore species and characterize their diets. We collected siphonophore specimens using blue water diving and ROVs. We extracted DNA from the feeding bodies, then amplified and sequenced six barcode markers along the 18S gene. OTUs are being assigned to prey taxa using a local zooplankton database of 18S amplicons. We expect this method to detect both small prey and gelatinous prey overlooked by other methods. Our results may reveal hidden links between mesozooplankton and higher trophic levels in the midwater food-web. This study will improve our understanding of the role of siphonophores in the open ocean, and the importance of their local species diversity in the OCCC for nutrient flow and ecosystem functioning.

Jon Copley, University of Southampton; Adrian Glover, Natural History Museum, London; Maria Baker, University of Southampton

The deep-sea mining industry is interested in seafloor massive sulphide deposits, formed at hydrothermal vents, which display high abundances of highly-specialised, often endemic fauna. The industry regulator, the International Seabed Authority, requires Contractors to undertake environmental baseline and monitoring studies within contract blocks, including quantifying diversity. These data, when combined with other global data sources, inform contract and regional level environmental management decisions. Species richness is the most common and straightforward measure for characterising the diversity of faunal assemblages, but this measure is highly affected by sampling effort. To overcome this issue, we can go back to our deep-sea biology roots. Rarefaction techniques can be used to compare species richness of samples collected with different sampling effort, and this study applies rarefaction tools to compare diversity at hydrothermal vents. Using data from UK-led cruises to hydrothermal vents in the North Atlantic, Southern Ocean, Indian Ocean, and Cayman Trough, where complete records of sampling effort (individual samples and numbers of ROV dives) are available, we applied rarefaction to estimate: (1) species richness of individual vent fields, accounting for variation in sampling effort; (2) levels of sample completeness; and (3) additional samples required to obtain certain levels of sample completeness. Our study focuses on vent endemic fauna at the species level, and will be expanded to include additional vent fields and biogeographic provinces where data are available. This study will develop tools to aid environmental management at local (Contractor) and regional (REMP) levels, enabling assessments of whether an area has been sufficiently sampled to reveal diversity levels, determining how much additional sampling may be required to achieve that goal, and informing management decisions with diversity estimators that account for variation in sampling effort.

Shannon Johnson, MBARI, Moss Landing; Warren Francis, University of Southern Denmark; Jacob Winnikoff, MBARI; Darrin Schultz, MBARI; Steven Haddock, MBARI

Ctenophores (comb jellies) inhabit marine environments from the surface to the deep-sea and exhibit a wide range of different body morphologies. Many shallow-living species are well-studied, however, most deep-living ctenophores remain undescribed because specimens are difficult to access and are often damaged during collection. Sequence data from the nuclear 18S ribosomal gene have provided a molecular phylogenetic framework for the relationships within Ctenophora. However, 18S-rDNA genes from ctenophores are highly conserved, and an 18S-based phylogeny often does not discriminate between closely related genera. One example is the order Lobata, where many species and even some distinct genera have identical 18S sequences. As a result, a great deal of biodiversity within the phylum is overlooked. The “barcoding” mitochondrial gene cytochrome-c-oxidase subunit-1 (COI) is typically more useful for revealing intra-specific relationships across taxa. Due to high rates of mitochondrial evolution in ctenophores, many commonly used “universal” primers fail to amplify the COI locus. As a result, few COI sequences are present in public databases. The paucity of data are especially important with the advent of mitochondrial metabarcoding efforts, where ctenophores may be under-represented because they cannot be amplified by the commonly-used primers. For this study, we designed multiple new COI primers based on transcriptome data we obtained from a diverse set of ctenophores, including many deep-sea species. These primers provide COI sequence data across all major groups of ctenophores, echoing diversity observed with morphology in some lobate species that was not reflected in 18S data. Furthermore, the COI fragment revealed several cryptic species. As we continue to sequence a broader diversity of ctenophores, new sequence information will help with species identification and descriptions, and will also provide a better understanding of relationships within Ctenophora.

Hiromi Kayama Watanabe, JAMSTEC; Shannon B. Johnson, MBARI

Discovered just four decades ago, deep-sea chemosynthetic ecosystems are now known to include rich oases formed around a variety of environments such as hydrothermal vents, hydrocarbon seeps, and organic falls (e.g., whale and wood). Although molluscs are a major component of these ecosystems with hundreds of endemic species worldwide, few groups have achieved endosymbiosis, the singular constrained evolutionary pathway to successful exploitation of chemosynthetic energy. Among these, abyssochrysoid gastropods are especially intriguing, as abyssochrysoid genera restricted to chemosynthetic ecosystems have extremely diverse ways of life – for example Provanna include deposit feeders and grazers, Ifremeria relies on endosymbionts, and Rubyspira feeds on whale bones. In the present study, we quantitatively explore the anatomical modifications of abyssochrysoid snails with different ecology using 3D reconstruction based on cutting-edge synchrotron CT data, with a focus on the three abovementioned genera. The emphasis is on the digestive and respiratory systems which are highly modified in each genus, for example the extremely hypertrophied digestive system in Rubyspira associated with bone digestion and similarly hypertrophied gill in Ifremeria associated with its holobiont condition.

Amanda E. Bates, Department of Ocean Sciences, Memorial University of Newfoundland; Marina Carreiro-Silva; Daphne Cuvelier; Eva Giacomello; Christopher Pham; Rui Prieto; Ana Colaço, IMAR, Instituto do Mar, OKEANOS - Centro I&D da Universidade dos Açores

Community ecology based on biological and/or functional traits rather than taxonomic criteria informs general ecological patterns through the study of ecological niches, function, and resistance and resilience to perturbations. There are no repositories for diverse species traits from non-chemosynthetic deep-sea ridges and associated seamounts, where the impacts of current and prospective human activities (i.e., seabed mining, fishing, and climate change) accelerate. We built a trait database standardized across different groups of taxa (i.e., macro- and megafauna, demersal and pelagic fishes, and cetaceans) from Condor Seamount (Mid-Atlantic Ridge) to identify general ecological patterns in these settings. The selected traits described morphological, trophic, physiological, structural, and behavioural features and were extracted from the literature, biodiversity repository databases, and complemented with expert knowledge. To identify trade-offs and traits relevant to ecosystem function we investigated covariance among traits and between traits and functions. Larger cold-water coral species host more associated epifauna compared to smaller corals, and species with wider bathymetric range show a broader distribution range within the Azores. We expect the understanding of relationships across diverse taxa and functional diversity within the ecosystem will lead to improved conservation outcomes underpinned by management frameworks that are informed by hierarchical monitoring of where species occur and their traits.

Ulrike Hanz, NIOZ Royal Netherlands Institute for Sea Research ; Furu Mienis, NIOZ Royal Netherlands Institute for Sea Research ; Benjamin Mueller, University of Amsterdam,; Andre Franke, Institute of Clinical Molecular Biology, Kiel; Emyr Martyn Roberts, University of Bergen; Hans Tore Rapp, University of Bergen; Ute Hentschel, GEOMAR Helmholtz Centre for Ocean Research Kiel

Seamounts represent ideal systems to study the influence and interdependency of environmental gradients at a single geographic location. While it is known that seamounts are globally abundant structures, it still remains unclear how and to which extent the complexity of the seafloor is intertwined with the local oceanographic mosaic, biogeochemistry and microbiology of a seamount ecosystem. Hence, we aimed to explore whether and to what extent seamounts can have an imprint on the microbial community composition of seawater and of sessile benthic invertebrates, sponges. Seawater samples were collected at two sampling depths from a total of 19 sampling sites along Schulz Bank seamount, and analysed for microbial structure and nine biogeochemical parameters. The results of our study reveal a seamount effect on the microbial mid-water pelagic community at least 200 m above the seafloor. Further, we observed a strong spatial heterogeneity in the pelagic microbial landscape across the seamount, with planktonic microbial communities reflecting oscillatory and circulatory water movements, as well as processes of bentho-pelagic coupling. Depth, NO32-, SiO4-, and O2 concentrations differed significantly between the determined pelagic microbial clusters close to the seafloor, suggesting that these parameters were presumably linked to changes in microbial community structures. While sponge-associated microbial communities were found to be mainly species-specific, we also detected significant intra-specific differences between individuals, depending on the pelagic near-bed cluster they originated from. Over all, this study shows that topographic structures such as the Schulz Bank seamount can have an imprint on both the microbial community composition of seawater and of sessile benthic invertebrates (sponges) by an interplay between the geology, physical oceanography, biogeochemistry and microbiology of seamounts.

Clifton Nunnally, Louisiana Universities Marine Consortium; Granger Hanks, Louisiana Universities Marine Consortium; Craig McClain, Louisiana Universities Marine Consortium

Deep-sea food falls are known to have varying effects of enrichment and disturbance on benthic communities, as well as provide novel habitat structure. Previous food fall work has centered on large (e.g., whales) or small (e.g., kelp, fish, wood) food parcels, and the effect of intermediately sized carcasses on sediment macrofauna communities remains poorly understood. Here, we deployed an individual Alligator mississippiensis carcass as organic enrichment to an otherwise food-poor landscape in the deep Gulf of Mexico. Sediment cores collected at three distances from the alligator fall experiment following decomposition were used to describe changes in macrofauna abundance and alpha- and beta-diversity along a gradient from relatively high food content (nearest the carcass) to low food content (furthest from the carcass). We found that the carcass enriched nearby sediments up to three times more than the carbon content of the background seafloor. This enrichment allowed macrofauna communities closer to the alligator carcass to host both more individuals and more species. The alligator carcass drew in a suite of species unique from the background fauna. The results of this experiment show that large reptiles may represent a previously unknown, yet important, carbon pathway to deep-sea macrofauna communities.

Satoshi Mitarai, Okinawa Institute of Science and Technology; Verena Tunnicliffe, University of Victoria

Hydrothermal vent fields are discrete ‘oases’ of high biological productivity in the deep sea. Local communities of vent-endemic species are spatially isolated but demographically linked through planktonic larval dispersal forming multi-vent metacommunities. Understanding of connectivity between spatially distinct vent sites is important because it supports higher levels of local diversity and productivity while maintaining regional stability, all of which are targets of conservation management. Observations of species presence at vent sites in the North-West Pacific were used to infer connectivity, using network theory to detect biogeographic boundaries and assess the role of each vent site in maintaining connectivity across the region. Two complimentary networks were created; a bipartite network of species nodes with links to the vent site nodes at which they are present, and a dissimilarity network where vent site nodes are linked by edges that are weighted based on the pairwise similarity between their communities. The results suggest the presence of three distinct sub-regions within the North-West Pacific that are separated by both regional dispersal barriers and local environmental filters. Both networks show that a small number of vent sites play a disproportionately important role in maintaining regional connectivity while the bipartite network also identifies vent sites that are important for connectivity within their respective sub-region. These network methods show distinct advantages in the detection of biogeographic boundaries when compared to more commonly used hierarchical clustering approaches. Furthermore, they are able to compare the role of vent sites in driving regional and local connectivity, which is of particular value when prioritizing sites for conservation and predicting the multi-vent scale impacts from proposed deep-sea mining in the North-West Pacific.

Veerle A.I. Huvenne, National Oceanography Centre, University of Southampton Waterfront Campus; Katharine R. Hendry, School of Earth Sciences, University of Bristol, UK

Habitat complexity influences the diversity and abundance of biological assemblages, particularly those associated with the occurrence of vulnerable marine ecosystems (VMEs). Observations of VME indicator species have been reported on the continental slope offshore SW Greenland; a region characterised by high relief, rugged terrain and a strong current regime. Traditional sampling methods struggle in these conditions, hence the megabenthic community structure and relative abundance of VME indicator species in this region at depths >500 m remain relatively unquantified. Using seabed images collected by ROV in 655–954 m water depth, we identified the taxonomic composition and abundance of epibenthic megafauna on the flank of a cross-shelf glacial trough at Nuuk, SW Greenland. A total of 26,695 individuals from 294 morphospecies were recorded. The community is dominated by suspension feeders, particularly crinoids, brittle stars and demosponges. VMEs occur in low abundance, most notably an isolated patch of Desmophyllum pertusum on a vertical cliff. Hierarchical cluster analysis of standardised abundance data indicates that community structure changes with substrate and/or depth, resulting in different assemblage zones. The intermediate slope zone (700 – 890 m) hosts the highest diversity (H’) and the largest diversity of VME indicator species. The relationship between habitat complexity and observed community patterns was modelled using a distance-based linear model (DistLM). Dominant substrate type, slope angle and depth are the main factors correlated with the change in assemblage zones. Morphospecies abundance is highest on consolidated bedrock with high relief, centralised in the intermediate slope zone. Our results show that variation in geomorphology influences benthic habitat complexity by supporting unique assemblages, including VME indicator species. Knowledge of the occurrence and relative abundance of VMEs is crucial in conservation and management planning.

David Barnes, British Antarctic Survey, UK; James Bell, Centre for the Environment, Fisheries and Aquaculture Science, UK; Rebecca Ross, Institute of Marine Research, Norway; Kerry Howell, University of Plymouth

Although latitudinal and bathymetric species diversity gradients in the deep sea have been identified and investigated, studies rarely focus characterising these gradients across seamount and oceanic island ecosystems. Drop camera images from 39 transects were collected between 250 m and 950 m and are used to characterise species richness from nine seamounts and oceanic islands spanning 8 °S to 40°S within the EEZs of Ascension Island, Saint Helena and Tristan da Cunha. Linear modelling showed surface primary productivity and substrate hardness to both have significant positive effects on species richness, with significantly higher species richness being recorded in temperate latitudes. No significant relationship between species richness and depth is detected. Findings suggest that although traditional latitudinal gradients of deep-sea species richness may be adhered to within seamount/oceanic island ecosystems, bathymetric gradients are not identified.

Thomas G. Dahlgren, University of Gothenburg; Diva Amon, Natural History Museum; Regan Drennan, Natural History Museum; Jennifer Durden, National Oceanography Centre; Kirsty McQuaid, University of Plymouth; Muriel Rabone, Natural History Museum; Craig R. Smith, University of Hawai’i at Mānoa; Erik Simon-Lledó, National Oceanography Centre; Helena Wiklund, University of Gothenburg; Adrian G. Glover, Natural History Museum

There is a growing interest in the exploration of deep-sea mineral deposits, particularly on the abyssal plains of the central Pacific Clarion-Clipperton Zone (CCZ), which are rich in polymetallic nodules. To assist with the efficient management of this potential new industry, it is necessary to have accurate estimates of biodiversity, and to understand community structure, species ranges, and connectivity across a range of scales. The benthic megafauna plays an important role in the functioning of deep-sea ecosystems and represents an important component of the biodiversity. Megafaunal surveys in the area, from video and still images, have provided insight into the biodiversity and community structure, but the physical collection of samples of this fauna is still required to improve estimates of species richness and species ranges, and is very rarely carried out. Using a Remotely Operated Vehicle (ROV), we collected 55 specimens of benthic megafauna from seamounts and abyssal plains in three Areas of Particular Environmental Interest (APEI-1, APEI-4, and APEI-7) at around 3100-5100 m depth in the western CCZ. We found, using both morphological and molecular evidence, 49 different species belonging to five phyla, of which only eight represented known species, with the rest representing species new to science.

Thomas Dahlgren, University of Gothenburg; Jeffrey C. Drazen, University of Hawai’i at Mānoa; Regan Drennan, Natural History Museum; Tammy Horton, National Oceanography Centre; Kirsty McQuaid, University of Plymouth; Craig R. Smith, University of Hawai’i at Mānoa; Sergio Taboada, Natural History Museum; Helena Wiklund, University of Gothenburg; Adrian G. Glover, Natural History Museum

In the last few years, there has been a resurgent interest in the exploration of deep-sea mineral deposits, particularly polymetallic nodules in the Clarion-Clipperton Zone (CCZ) in the central Pacific. Critical to the effective management of a new industry is accurate environmental impact assessment, dependent on a sound understanding of species taxonomy, biogeography, and connectivity across a range of scales. Connectivity is one of the most important parameters in determining ecosystem resilience, as it helps to define the ability of a system to recover post-impact. Scavenging amphipods in the superfamilies Alicelloidea and Lysianassoidea are quite abundant and play an important role in deep-sea ecosystems. They are relatively easy to sample and, in recent years, have become the target of several molecular and taxonomic studies. But in the CCZ they are poorly studied. Here, we use a molecular approach to identify and delimit species, and to investigate evolutionary relationships of the scavenging amphipods from both abyssal plain and deep (>3000m) seamount habitats in three APEIs (Areas of Particular Environmental Interest) in the western CCZ. We also assess connectivity within and between these regions, spanning about 1500 km. We found 17 different species, including the most common species reported for other basins, as well as all of the species previously reported for the eastern CCZ. Only four species are shared between the three sites. The two abyssal plain sites analysed are dominated by common species, while the seamount site is dominated by new species not shared with the abyssal plains. The presence of the most common species in all sites, as well as shared haplotypes, indicates connectivity over evolutionary time scales between the regions. Similarly to recent studies, the differences in amphipod assemblages we find between seamount and abyssal sites suggests that ecological conditions on seamounts yield distinct community composition.

Natasha Karenyi, University of Cape Town

Offshore marine invertebrates are the most understudied group of organisms despite occupying the most expansive habitat on the planet. The offshore sea floor of South Africa is largely unexplored, with most benthic marine invertebrate samples limited to depths shallower than 100 m. The aim of this project is to explore the macrobenthic infaunal diversity of the Agulhas shelf edge for the first time. Seven grab samples were opportunistically collected along the shelf edge. Species were identified, counted and weighed. Using multivariate analysis techniques on biotic data acquired from the shelf edge grab samples, the patterns in infaunal diversity and their potential environmental drivers are explored. From this project, the first workable species list of the macrobenthic infauna of the shelf edge has been created. No distinct infaunal communities were clear from the data. Based on the species abundance data, the average similarity across the benthic shelf edge sites is 7.02 %. Contributing the greatest proportion to the similarity between sites (22.03 %) is the polychaete, Onuphis geophiliformis. Polychaeta are the most dominant group of organisms found, composing 48.18 % of the total abundance. The environmental drivers which best predict the diversity patterns across the shelf edge are depth and sediment grain size (ρ = 0.77). The environmental drivers can aid predictions of biodiversity patterns across the shelf edge where biological data is scarce.

Amanda Demopoulos, U.S. Geological Survey; Jason Chaytor, U.S. Geological Survey; Samantha Joye, University of Georgia; Jonathan Quigley, Cherokee Nation Technologies; Penny McCowen, U.S. Geological Survey; Erik Cordes, Temple University; Caroline Ruppel, U.S. Geological Survey

The occurrence of hundreds of methane seeps along the U.S. Atlantic margin extending from offshore New England to the Blake Ridge Diapir has prompted multiple investigations to characterize these habitats. Visual surveys using remotely operated and human occupied vehicles have confirmed seep communities, including deep-sea mussels, microbial mats, clam beds, and active methane bubbling habitats, which often represent different chemical environments related to variation in the flow of methane through sediments. However, infaunal communities have only been characterized at three sites, leaving gaps in our understanding of the broad-scale relationships between benthic communities, localized geochemical environments, and regional connectivity among taxa. Between 2015 and 2019 sediments were collected from seep habitats at 12 sites along the western Atlantic margin encompassing a depth range of 227-2592m. Sediments were assessed for macrofaunal abundance, diversity, and community structure, and corresponding sediment physical and geochemical properties. This is the first large-scale study to investigate seep communities across a broad latitudinal and depth gradient. Record high densities of macrofauna were observed at shallow seeps, with overall lower abundance at deep seeps indicating a potential relationship to surface productivity. Patterns of community structure related to depth, geographic separation, habitat heterogeneity, and geochemical drivers will be discussed. This work enhances our understanding of the large-scale and fine-scale environmental controls on diversity and community composition in seep habitats and the overall regional connectivity among seep environments. As seeps provide a unique environment that enhances the broader biodiversity and supports multiple ecosystem services provided by the deep sea, an increased understanding of the relationships among habitats will better inform effective management and conservation strategies for the deep sea.

Malcolm Clark, National Institute of Water and Atmospheric Research; Ashley Rowden, NIWA; Jonathan Gardner, Victoria University of Wellington

The deep sea is subject to multiple anthropogenic disturbances, including potential mining of hydrothermally-formed seafloor massive sulfides (SMS). As a first step towards a full Ecological Risk Assessment (ERA) for SMS exploitation, faunal sensitivity to mining activities was assessed based on the functional traits of epibenthic megafauna. Faunal distribution and abundance data at two different spatial scales were used from video surveys conducted at SMS deposit-hosting seamounts on the Kermadec Arc, New Zealand. For each taxon, sensitivity was scored for six functional traits: adult size, environmental position, living habit, feeding habit, mobility, and structural fragility. Sensitivity was scored separately for three mining disturbances: passage of mining vehicles along the seafloor, sediment plumes generated by mining activity, and mineral extraction. Sensitivity to mining impacts was summed within samples and mapped to show the spatial distribution of assemblage sensitivity. For both spatial scales, the sensitivity of taxa and the sensitivity summed within each assemblage was greatest to mineral extraction, followed by plume impacts, with the least sensitivity to vehicle impacts. The location of most very highly sensitive assemblages coincided with the occurrence of hydrothermal vent fauna and hydrothermally active habitat. Highly sensitive assemblages occurred at hydrothermally inactive sulfide structures, such as chimneys, and other locations where assemblages were dominated by fragile, sessile, suspension-feeding taxa, such as scleractinian branching corals. The approach taken here illustrated spatial patterns in sensitivity within seamounts and sites and provides an important first step towards a more comprehensive ERA. This assessment has the potential to inform decisions on spatial management of SMS mining activities, and the suitable placement of area-based management measures, such as marine protected areas.

Jordi Grinyo, Institute of Marine Sciences, CSIC, Barcelona,Spain; Stefano Ambroso, CSIC; Claudio Lo Iacono, CSIC; Veerle Huvenne, National Oceanography Centre; Marie-Claire Fabri, Ifremer; Ruth Duran, CSIC; Albert Palanques, CSIC; Andrea Gori, University of Barcelona; Stefano Piraino, University of Salento, Lecce, Italy; Sergio Rossi, University of Salento; Jose-Maria Gili, CSIC; Pere, Puig, CSIC

The Blanes Canyon is located in Northwest Mediterranean, and incises the Catalan margin. Bottom trawling is a common activity in the area, frequently occurring around the canyon rims and flanks, and causing resuspension of a substantial amount of sediment within the canyon. The present study is based on the analysis of video transects performed with the ROV Liropus 2000 in the Blanes Canyon, between 600 and 1100 m depth, in order to characterize cold water coral (CWC) communities in a region undergoing severe human pressure. Structurally controlled vertical walls have been observed to provide suitable habitat for a wide variety of CWCs, forming rich communities that are internationally recognized as Vulnerable Marine Ecosystems (VMEs). Major communities consisted of the reef-forming species Lophelia pertusa and Madrepora oculata, the solitary scleractinian Desmophyllum dianthus and the black coral Leiopathes glaberrima. Our findings highlight the importance of deep-sea canyons acting as refuge for CWC communities, which however suffer from the indirect impacts of fishing activities, such as sediment resuspension and lost fishing gear.

Ashley Rowden, Victoria University of Wellington, National Institute of Water and Atmospheric Research; David Bowden; Daniel Leduc, National Institute of Water and Atmospheric Research

Turbidity flows – underwater avalanches – are large-scale disturbance events that are believed to have profound and lasting impacts on benthic communities in the deep sea. However, only a few of these flows have ever been studied and most of the hypotheses about the effects of turbidity flows on benthic communities come from studies of events that occurred hundreds to thousands of years ago. Moreover, studies of more recent turbidity flows lack data from before the turbidity flow occurred, which are necessary to truly understand the resilience, or lack thereof, of a community to these large-scale disturbances. An earthquake in 2016 which triggered a turbidity flow in Kaikōura Canyon (New Zealand) presents a unique opportunity to study immediate and medium-term impacts on benthic communities. A time-series of photographic transects and sediment cores collected before and after the event are the basis of a study which aims to build models predicting rates of benthic community recovery from large disturbances in the deep sea. These models will contribute to better understanding of natural disturbances from turbidity flows and will be useable as proxies for anthropogenic disturbance from seabed mining. Preliminary results of megafauna resilience from the photographic transects are presented. Megafauna appear to be in the early stages of recovery, and temporary chemosynthetic habitats and communities have arisen.

Brendan Roark, Texas A & M University; Amy Baco-Taylor, Florida State University

Deep sea bottom contact fisheries leave large patches of disturbed substrate void of megafauna. It had been hypothesized that life history characteristics of dominant benthic megafauna on seamounts would result in little or no recovery of these communities from this disturbance. A recent study has countered this prediction with observations of some recovery on protected seamounts on 30-40 year time scales. However the scale of taxonomic resolution in that study prevented addressing whether seamount communities were recovering to the same or an alternate state. Starting in the 1960s, seamounts of the Northwestern Hawaiian Islands (NWHI) and lower Emperor Seamount Chain (ESC) were heavily targeted for fisheries trawling and tangle net dragging for precious corals. The widespread impacts to hard substrate coral and sponge communities on these seamounts has enabled the investigation of natural recovery and resilience to large scale disturbance. Seamounts were separated into three treatment groups based on historical fishing effort; Never Trawled, Recovering, and Still Trawled. Recovering seamounts have had 30-40 years to recover since the establishment of the US EEZ in 1977. Using the Pisces IV and V submersibles, replicate 500m length transects were collected from each seamount at a depth of 500m on the same sides of each seamount. These were then annotated for species composition and abundance. Preliminary results from 11 transects show abundance was highest on the Still Trawled seamounts and lowest on the Recovering seamounts. Diversity was highest on Yuryaku seamount, one of the still trawled sites, but in an area that was naturally protected from trawling by steep topography. Based on cluster analyses, community structure on the recovering seamounts was more similar to the never trawled seamounts than to the still trawled. This suggests communities on the recovering seamounts are recovering to the same state. Further data analyses are needed to verify these results

Patricia Blackwelder; Tracey Sutton; Natalie Slayden; Jose Lopez, Nova Southeastern University

The pelagic tunicate, Pyrosoma atlanticum, is known for its brilliant bioluminescence, but the mechanism causing this bioluminescence has not been fully characterized. This study identifies the bacterial bioluminescent symbionts of P. atlanticum collected in the northern Gulf of Mexico using several methods such as light and electron microscopy, as well as molecular genetics. The bacteria are localized within the pyrosome light organs. Greater than 50% of the bacteria taxa present in the tunicate samples (n=3) were the bioluminescent symbiotic bacteria Vibrionaceae as determined by utilizing current molecular genetics methodologies. A total of 396K MiSeq16S rRNA reads provided total pyrosome microbiome profiles to determine bacterial symbiont taxonomy. After comparing with the Silva rRNA database, a 99% sequence identity matched a Photobacterium sp. R33-like bacterium (which we refer to as Photobacterium Pa-1) as the most abundant bacteria within P. atlanticum samples. Specifically-designed 16S rRNA V4 probes for fluorescence in situ hybridization (FISH) verified the Photobacterium Pa-1 location as internally concentrated along the periphery of each pyrosome luminous organ. While searching for bacterial lux genes in 2 tunicate samples, we also serendipitously generated a draft tunicate mitochondrial genome which was used for P. atlanticum pyrosome identification. Scanning (SEM) and transmission (TEM) electron microscopy confirmed the presence of intracellular rod-like bacteria in the light organs. This intracellular bacterial localization may represent a bacteriocyte formation reminiscent of other invertebrates.

Uwe Wolfram, Heriot-Watt University; J. Murray Roberts, University of Edinburgh; Sebastian Hennige, University of Edinburgh

Framework-forming species of cold-water corals (CWC) like Lophelia pertusa create deep sea biodiversity hotspots by providing habitats for thousands of species. However, climate change threatens CWC and the ecosystem services they provide. To quantify global driver threats, previous studies have explored impacts of increased temperature, decreased pH, and decreased oxygen on both live and dead corals. This review synthesizes physiological response experiments to date which have varied results that can be explained by stressor exposure time with short-term studies eliciting negative responses and longer-term experiments indicating CWC can undergo acclimatization to a limited degree. While short-term exposure (≤ 1 month) to increased temperatures saw decreased respiration rates and increased mortality, CWC showed acclimatization during longer-term studies (> 1 month) to temperatures comparable to end-of-century projections. Similarly, while the majority of short-term decreased pH studies found depressed calcification rates, many of which experienced net dissolution, most CWC acclimatized to aragonite undersaturated waters in long-term experiments. However, despite living CWC’s ability to grow in low pH conditions, ocean acidification threatens dead exposed skeleton lacking protective tissue with dissolution, decreasing reef framework structural integrity. Deoxygenation remains understudied, with only two published laboratory-based studies, which found negative impacts on respiration and survivorship. These findings suggest deoxygenation may limit living CWC ranges while decreased pH may determine dead reef framework functionality. Areas for further study include multiple stressors, long-term experiments, dead skeleton responses, lesser- studied species, and CWC collected from the global south.

Aluwani Nemukula, University of KwaZulu-Natal, Westville; David Glassom, University of KwaZulu-Natal, Westville

Ocean temperatures continue to rise due to global climate change and anthropogenic activities, resulting in coral bleaching even mortalities. Symbiotic microalgae (zooxanthellae) living within reef-building corals are responsible for photosynthesis, contributing to coral bleaching tolerance. Our study investigated physiological response of zooxanthellae to elevated temperatures, using data of maximum quantum yield (Fv/Fm) for photosynthetic health fitness and non-photochemical quenching (NPQ) for excess energy dissipation. Massive A. irregularis and branching P. verrucosa were collected from the south coast of KwaZulu-Natal. Zooxanthellae were prepared and exposed to ambient (26°C) and elevated (30, 32 and 34°C) temperatures in cultures for 28 days and within colonies for 5 days, respectively. Fv/Fm and NPQ were regularly measured with PAM-fluorimeter. Zooxanthellae in cultures and within corals achieved highest Fv/Fm at 26, 30 and 32°C, falling within 50-80% reported for healthy corals than 34°C. Branching (e.g., Acropora) and massive (e.g., Dipsastraea) corals similarly showed high tolerance at 30-32°C. Fv/Fm was below 50% at 34°C, indicating signs of photosynthetic damage often linked to coral bleaching. In parallel, zooxanthellae had highest NPQ, indicating susceptibility at 34°C than 26, 30 and 32°C. Zooxanthellae of A. irregularis attained higher Fv/Fm, showing better physiology adjustments than those of P. verrucosa. Differential responses could be associated with differing zooxanthellae clades, coral morphologies, tissue thickness and adaptations. The study suggests zooxanthellae of either species can determine coral bleaching tolerance, achieving maximum photosynthesis at 26-32°C. Further, massive corals seemed more robust than branching corals to thermal stress. Scientists, coral and environmental managers should use and expand present results to better predict and mitigate impact of climate change.

Rita Vargas-Castillo, Museo de Zoología, Escuela de Biología, Universidad de Costa Rica

This study reports on the re-discovery of 33 crustacean specimens collected during the 1973 expedition onboard the MY Velero IV from deep-sea waters in the Pacific of Costa Rica, which were accidentally stored in a fish collection, where remained unidentified. A total of 13 species were identified: seven krill species (family Euphausiidae), five shrimp species (two Benthesicymidae, two Sergestidae, and one Acanthephyridae), and one swimming crab of the family Portunidae. Four species were new records for Costa Rica: Bentheogennema burkenroadi, Gennadas scutatus, Neosergestes consobrinus, and Phorcosergia filicta.

Juan Carlos Azofeifa-Solano, Universidad de Costa Rica; Yolanda E Camacho-García, Museo de Zoología, Escuela de Biología, Universidad de Costa Rica; Ingo S. Wehrtmann, Unidad de Investigación Pesquera y Acuicultura (UNIP), Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), Universidad de Costa Rica

The deep sea is the least studied and most vulnerable realm on Earth. Latin American deep-sea fisheries have limited bycatch data, and knowledge on associated molluscs is often non-existent. The resent study provides information on deep-sea shelled molluscs collected by commercial shrimp trawlers during 2010 and 2011 between 112 and 271 m depth. A total of 26 species were identified, with 23 gastropods and three bivalves. These collections support a depth range extension for 14 species. In addition, Homalopoma cf. gripii is reported for the first time in Costa Rica. The most abundant species were Fusinus spectrum, Polystira nobilis, and Solenosteira gatesi. Only Sinum debile was collected deeper than 250 m. The catch per unit effort of benthic shelled molluscs in the deep-sea shrimp fishery in Costa Rica was influenced by depth, while seasonality or region showed no influence. It is suggested that long-lasting trawling practices on the deep-sea bottoms might have caused negative effects on molluscs’ diversity and biomass, and a monitoring program is needed to assess these possible impacts.

Mary Deere, Department of Biology, Temple University; Odalisca Breedy, Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), Universidad de Costa Rica; Jorge Cortés, CIMAR, Universidad de Costa Rica; Erik Cordes, Department of Biology, Temple University

Oxygen minimum zones (OMZs) are among the most significant abiotic environmental gradients found in the deep ocean. In the eastern tropical Pacific, species distribution records of important habitat-forming megafauna, like deep-water corals, inhabiting OMZs are limited thus hindering our understanding of how sharp oxygen gradients influence community composition and diversity. To better understand this relationship for deep-water corals off Costa Rica, we analyzed seafloor video and associated collections across bathyal depths from a 2019 R/V Falkor cruise using the ROV SuBastian. At 8 seamounts off the Costa Rica margin and one canyon north of Cocos Island, we observed 3675 coral occurrences and identified 75 morphospecies between 177-1565 m. Assemblages within OMZ depths (300-700 m) were observed to be significantly different from those at deeper bathyal depths. Upper and lower OMZ boundaries saw the most rapid rates of species turnover across all sites and indicated a strong sensitivity of some coral taxa, such as colonial scleractinians, to the lowest concentrations of dissolved oxygen. Stylasterid hydrocorals were disproportionately abundant above and within the OMZ, while octocoral and black coral species dominated in the more oxygenated waters below. Coral assemblage diversity and species abundances were both depressed within the OMZ, but diversity metrics rebounded at mid-bathyal depths between 1200-1500 m. These results highlight the importance of seamount OMZ communities in increasing regional deep-water coral diversity and provide new insight to the drivers of deep-water coral community assembly in a data-deficient locality. In addition to informing marine conservation and management efforts off Costa Rica, these baseline datasets are pertinent to evaluating change in deep-sea benthic communities in response to expansion and intensification of the eastern tropical Pacific OMZ from ocean warming and other climate-linked drivers.

Shuzhe Guan, Scripps Institution of Oceanography; Dante Capone, University of California Santa Cruz; Katherine Rigney, Carleton College, Minnesota; Katelynn Rowley, Scripps Institution of Oceanography; Victoria Orphan, California Institute of Technology; Sean Mullin, California Institute of Technology; Kat Dawson, Rutgers University, New Jersey; Jorge Cortés, Centro de Investigación en Ciencias del Mar y Limnología, Universidad de Costa Rica; Greg Rouse, Scripps Institution of Oceanography; Guillermo Mendoza, Scripps Institution of Oceanography; Raymond Lee, Washington State University; Lisa Levin, Scripps Institution of Oceanography

Ecotones have been described as ‘biodiversity hotspots’ from myriad environments, yet have not been studied extensively in the deep ocean. Whilst physiologically challenging, methane seeps host highly productive communities fuelled predominantly by chemosynthetic pathways. We hypothesised that the biological and geochemical influence of methane seeps extends into background habitats, resulting in the formation of a ‘chemotone’ where chemosynthesis-based and photosynthesis-based communities overlap. To investigate this, we analysed the macrofaunal assemblages and geochemical properties of sediments collected from ‘active’, ‘transition’ (potential chemotone) and ‘background’ habitats surrounding five Costa Rican methane seeps. Sediment geochemistry demonstrated a clear distinction between active and transition habitats, but not between transition and background habitats. In contrast, biological variables confirmed the presence of a chemotone, characterised by intermediate biomass, a distinct species composition (including habitat endemics and both active and background species), and enhanced variability in species composition among samples. However, chemotone assemblages were not distinct from active and/or background assemblages in terms of faunal density, biological trait composition or diversity. Biomass and faunal stable isotope data suggest that chemotones are driven by a gradient in food delivery from chemosynthetic production towards lower quantity and quality photosynthetic-based resources. Our findings suggest that chemosynthetic food supplements are delivered across the chemotone at least in part through the water column, as opposed to reflecting exclusively in situ chemosynthetic production in sediments. Management efforts should be cognisant of the ecological attributes and spatial extent of the chemotone that surrounds deep-sea chemosynthetic environments.

Aaron Lim, University College Cork; Kimberley Harris, University College Cork; Ruth O'Riordan, University College Cork; Luke O'Reilly, University College Cork; Andrew Wheeler, University College Cork

Submarine canyons support high biomass communities as they act as conduits where sediments, nutrients and organic matter from continental shelves, or carried by along slope currents, are transported into the abyssal zone. The Porcupine Bank Canyon (PBC), located on the Irish continental margin, reveals a complex terrain and variable substrata that affect the distribution of benthic fauna. Here, ROV based benthic video, Conductivity-Temperature-Depth (CTD) and bathymetric data were assessed to show the effects of environmental processes on the distribution of benthic megafauna throughout the canyon. Multivariate analysis of the benthic community reveals significant (0.091 < R < 0.166, P < 0.05) differences in the community structure between the habitats throughout the canyon. Furthermore, the analysis shows that non-coral habitats exhibit more variation in the composition of benthic taxa than coral habitats, with the following taxa most contributing to the structural differentiation: Leiopathes glaberrima (12.46%), Hexadella dendritifera (10.37%), Cidaris cidaris (9.31%), Aphrocallistes beatrix (9.33%), Areaosoma fenestratum (9.11%), Stichopathes cf. abyssicola (7.39%), Anthomastus glandiflorus (4.66%) and Benthogonea rosea (3.84%). In addition, bathymetric variables (depth, slope), habitats and sites are the most important environmental drivers that affect benthic taxa distribution in the PBC. Habitat variability, bathymetry and oceanographic processes most likely control benthic taxa distribution in the canyon. The findings of the current study will inform fishermen on how to responsibly interact with the canyon and can help inform policy makers on the effective management of the cold water coral (CWC) environment in the PBC.

Heather Coleman, NOAA Deep Sea Coral Research and Technology Program; Thomas Hourigan, NOAA Deep Sea Coral Research and Technology Program; Mashkoor Malik, NOAA Office of Exploration and Research

The deep sea appears far-removed from anthropogenic impacts, yet deep-sea habitats face similar threats to shallow-water habitats such as fishing stress, ocean acidification, and pollution. Deep-sea coral and sponge ecosystems are often hotspots of biodiversity, providing habitat for invertebrates and fishes, including those of commercial importance. Thus, species that are vital to the U.S. economy may also be threatened by anthropogenic impacts such as marine debris. Few studies examine the relationship between marine debris and deep-sea coral and sponge habitats because these ecosystems are difficult and expensive to study. I conducted an analysis of the past six years of NOAA Ship Okeanos Explorer ROV video data, discerning all observed instances of marine debris to examine its association with deep-sea corals and sponges in the U.S. Northeast and Southeast, Gulf of Mexico, and Caribbean regions. The largest category of observed debris was plastic, 71.9% being single-use plastics. Several debris items were entangled around corals and sponges, while others provided new substrata for coral and sponge settlement, allowing for the possibility of invasive species transport around the globe. Images of debris and managed species associated with deep-sea corals and sponges can be used to inform policy and the public on the importance of protecting deep-sea coral habitats from anthropogenic impacts using tools such as Habitat Areas of Particular Concern and Marine National Monuments.

Francis Marsac, Institut de Recherche pour le Développement (Sète, France); Jean-François Ternon, Institut de Recherche pour le Développement; Anne Lebourges-Dhaussy, UMR LEMAR, IRD/CNRS/UBO/Ifremer; Gildas Roudaut, UMR LEMAR, IRD/CNRS/UBO/Ifremer; Steven Herbette, UMR LOPS, UBO/IRD/Ifremer/CNRS; Yves Cherel, Centre d’Etudes Biologiques de Chizé; Evgeny Romanov, CAP RUN – Hydrô Réunion, Le Port, Île de la Réunion, France

Seamounts are ubiquitous topographic features across all ocean basins. Depending on their size, shape and summit depths, seamounts have an impact on the physical flow regimes. Some seamounts located in the Atlantic and Pacific oceans have been shown to promote the aggregation of zooplankton, micronekton, and top predators above or in the immediate vicinity of their summits. The dynamics of micronekton was investigated as part of a multi-disciplinary research project carried out at two shallow seamounts of the south-western Indian Ocean: La Pérouse (summit depth, ~60m) and MAD-Ridge (summit depth, ~240m), located in contrasting biogeochemical provinces. Micronekton was sampled using an International Young Gadoid Pelagic Trawl, towed for 30 min-1 hour at a speed of 3-4 knots. Acoustic data were collected continuously during the day and night at 4 frequencies: 38, 70, 120 and 200 kHz at both seamounts. The published results from this study demonstrate the influence of cyclonic eddies in concentrating micronekton in the top 200 m of the water column during day time compared to the anticyclone which resulted in micronekton being concentrated below 400 m during daytime, and the influence of seamounts, aggregating specific communities of fishes (responding equally to the 38, 70 and 120 kHz frequencies) over their summits and flanks. A greater micronekton acoustic density was recorded at MAD-Ridge compared to La Pérouse owing to the differing environmental characteristics of these two seamount ecosystems. Published results do not show any enhanced biomass of micronekton at La Pérouse and MAD-Ridge, as reported to be the case for other seamounts. This study therefore suggested that seamount-associated species were the only seamount effect detected and that in a highly dynamic environment like south of Madagascar, mesoscale features have a stronger influence than seamounts on micronekton acoustic densities.

Florence Pradillon, Ifremer; Daniela Zeppilli, Ifremer; Loïc N. Michel, Ifremer; Pedro Martinez Arbizu, Senckenberg am Meer; Hayato Tanaka, Tokyo Sea Life Park; Martin Foviaux, Ifremer; Jozée Sarrazin, Ifremer

Productivity and environmental stress are major drivers of multiple biodiversity facets and faunal community structure. Little is known on their interacting effects on early community assembly processes in the deep sea. However, at hydrothermal vents productivity correlates, at least partially, with environmental stress. Here, we studied the colonization of rock substrata deployed along a deep-sea hydrothermal vent gradient at four sites with and without direct influence of vent fluids at 1700 m depth in the Lucky Strike vent field (Mid-Atlantic Ridge, MAR). We examined in detail the composition of faunal communities (>20 m) established after two years and evaluated species and functional patterns. We expected the stressful hydrothermal activity to (1) limit functional diversity and (2) filter for traits clustering functionally similar species. However, our results show that hydrothermal activity enhanced functional diversity. Moreover, despite high species diversity, environmental conditions at sites without direct vent influence appear to filter for specific traits, thereby reducing functional richness. In fact, diversity in ecological functions may relax competition allowing several species to coexist in high densities in the reduced space of the highly-productive vent habitats under direct fluid emissions. We suggest that the high productivity at fluid-influenced sites supports higher functional diversity and traits that are more energetically expensive. The observed faunal overlap and energy links (exported productivity) suggest that rather than operating as separate entities, habitats with and without influence of hydrothermal fluids may be considered as interconnected entities. Low functional richness and environmental filtering suggests that surrounding areas, with their very heterogeneous species and functional assemblages, may be especially vulnerable to environmental changes related to natural and anthropogenic impacts, including deep-sea mining.

Koeda Keita, Kuroshio Biological Research Foundation; Senou Hiroshi, Kanagawa Prefectural Museum of Natural History; Kikuchi Kiyoshi, Fisheries Laboratory / The University of Tokyo; Hirase Shotaro, Fisheries Laboratory / The University of Tokyo

Morphological identification of deep-sea fishes is difficult due to taxonomic confusion and/or their poor diagnostic features. COI-based DNA barcoding could not only be an efficient tool for species identification of deep-sea fishes, but could also lead to the discovery of their novel species diversity. However, the availability of reference sequences of deep-sea fishes for DNA barcoding is limited, especially for fishes in the Northwest Pacific Ocean. In this study, we performed COI-based DNA barcoding of mesopelagic and demersal fish species on the continental shelf and upper slope, collected by deepwater fisheries around Japan and Taiwan, to accumulate the reference sequences of the Northwest Pacific deep-sea fishes. Overall, we obtained COI sequences of 124 species from 64 families. We examined the genetic diversity within each species for which COI sequences were obtained from multiple specimens and found that Chimaera phantasma, Harpadon microchir, and Pyramodon ventralis showed high intraspecific genetic divergences of more than 2% Kimura 2-parameter distance. Among them, C. phantasma and H. microchir showed genetic divergences between the specimens from Japanese waters and Taiwanese waters, and P. ventralis had two genetic lineages that are distributed sympatrically around the Japanese waters. Moreover, for 19 cosmopolitan fishes, a comparison between our data and previously acquired COI sequence data suggested a high level of genetic differentiation between the Northwest Pacific Ocean and other oceans in each cosmopolitan species. These results suggest that several cryptic species have not yet been discovered in deep-sea fishes.

Ryan M. Young, National University of Ireland Galway; Nicole Avalon, University of South Florida; Mark Johnson, National University of Ireland Galway; Bill Baker, University of South Florida; Olivier Thomas, School of Chemistry and Ryan Institute, National University of Ireland Galway; Louise Allcock, School of Natural Sciences and Ryan Institute, National University of Ireland Galway

Samples of marine sponges and corals were collected from biogenic and geogenic reefs, ranging in depths from 1,000 – 3,000 m, as part of a program aimed at the discovery of bioactive metabolites through characterizing hotspots of biological and chemical diversity in the deep-sea of the North Eastern Atlantic Ocean. These organisms have developed unique specialized metabolites to compete for space and to defend against predation. These factors, combined with metabolic adaptations required to live in the extreme physical conditions of the deep sea, drive secondary metabolite production, some with potent bioactivity. We have observed a high rate of bioactivity when testing extracts from a broad range of corals and sponges against various diseases, including a range of cancers, viruses, and bacteria such as ESKAPE pathogens. Active extracts and fractions were further purified to allow the discovery of new bioactive specialized metabolites with unique chemical structures. These include novel glycolipopeptides isolated from the Tetractinellida Characella pachastrelloides (Carter, 1876) which have potent anti-inflammatory activity, new steroids active against C. difficile, from the bamboo coral Jasonisis sp., and brominated tyrosine derivatives from zoantharians, which activate the apoptosome resulting in the initiation of cell death.