Search

Background: Coral-associated microbiomes vary greatly between colonies and localities with functional consequences on the host. However, the full extent of variability across the ranges of most coral species remains unknown, especially for corals living in deep waters which span greater ranges. Here, we characterized the microbiomes of four octocoral species from mesophotic and bathyal deep-sea habitats in the northern Gulf of Mexico, Muricea pendula, Swiftia exserta, Callogorgia delta, and Paramuricea biscaya, using 16S rRNA gene metabarcoding. We sampled extensively across their ranges to test for microbiome differentiation between and within species, examining the influence of environmental factors that vary with depth (53–2224 m) and geographic location (over 680 m) as well as the host coral's genotype using RAD-sequencing. Results: Coral microbiomes were often dominated by amplicon sequence variants whose abundances varied across their hosts' ranges, including symbiotic taxa: corallicolids, Endozoicomonas, members of the Mollicutes, and the BD1-7 clade. Coral species, depth, and geographic location significantly affected diversity, microbial community composition, and the relative abundance of individual microbes. Depth was the strongest environmental factor determining microbiome structure within species, which influenced the abundance of most dominant symbiotic taxa. Differences in host genotype, bottom temperature, and surface primary productivity could explain a significant part of the microbiome variation associated with depth and geographic location. Conclusions: Altogether, this work demonstrates that the microbiomes of corals in deep waters vary substantially across their ranges in accordance with depth and other environmental conditions. It reveals that the influence of depth on the ecology of mesophotic and deep-sea corals extends to its effects on their microbiomes which may have functional consequences. This work also identifies the distributions of microbes including potential parasites which can be used to inform restoration plans in response to the Deepwater Horizon oil spill. [ABSTRACT FROM AUTHOR]

In this catalogue, 80 species of ophiuroids collected by the IN2021_V04 and IN2022_V08 expeditions to the Australian Christmas Island and Cocos (Keeling) Islands Territories are described and illustrated. [ABSTRACT FROM AUTHOR]

Environmental DNA metabarcoding reveals a vast genetic diversity of marine eukaryotes. Yet, most of the metabarcoding data remain unassigned due to the paucity of reference databases. This is particularly true for the deep-sea meiofauna and eukaryotic microbiota, whose hidden diversity is largely unexplored. Here, we tackle this issue by using unique DNA signatures to classify unknown metabarcodes assigned to deep-sea foraminifera. We analyzed metabarcoding data obtained from 311 deep-sea sediment samples collected in the Clarion-Clipperton Fracture Zone, an area of potential polymetallic nodule exploitation in the Eastern Pacific Ocean. Using the signatures designed in the 37F hypervariable region of the 18S rRNA gene, we were able to classify 802 unassigned metabarcodes into 61 novel lineages, which have been placed in 27 phylogenetic clades. The comparison of new lineages with other foraminiferal datasets shows that most novel lineages are widely distributed in the deep sea. Five lineages are also present in the shallow-water datasets; however, phylogenetic analysis of these lineages separates deep-sea and shallow-water metabarcodes except in one case. While the signature-based classification does not solve the problem of gaps in reference databases, this taxonomy-free approach provides insight into the distribution and ecology of deep-sea species represented by unassigned metabarcodes, which could be useful in future applications of metabarcoding for environmental monitoring. [ABSTRACT FROM AUTHOR]

Seamounts are thought to function as hotspots of megafauna diversity due to their topology and environmental characteristics. However, assessments of megafauna communities inhabiting seamounts, including diversity and density, are scarce. In this study, we provide megafauna diversity and density estimates for a recently discovered, not yet characterized seamount region (Boetius seamounts) west of Cape Verde (N17° 16′, W29° 26′). We investigated the distribution of epibenthic megafauna over a large depth gradient from the seamount’s summit at 1400 m down to 3200 m water depth and provided qualitative and quantitative analyses based on quantified video data. In utilizing an ocean floor observation system (OFOS), calibrated videos were taken as a horizontal transect from the north-eastern flank of the seamount, differentiating between an upper, coral-rich region (−1354/−2358 m) and a deeper, sponge-rich region (−2358/−3218 m). Taxa were morphologically distinguished, and their diversity and densities were estimated and related to substrate types. Both the upper and deeper seamount region hosted unique communities with significantly higher megafauna richness at the seamount’s summit. Megafauna densities differed significantly between the upper (0.297 ± 0.167 Ind./m2) and deeper community (0.112 ± 0.114 Ind./m). The seamount showed a vertical zonation with dense aggregations of deep-sea corals dominating the seamount’s upper region and colonies of the glass sponges Poliopogon amadou dominating the deeper region. The results are discussed in light of detected substrate preferences and co-occurrence of species and are compared with findings from other Atlantic seamounts. [ABSTRACT FROM AUTHOR]

Cephalopods form important components of marine trophic systems worldwide, including those in the South Pacific. Moroteuthopsis ingens (Onychoteuthidae) is one of the most abundant deep–sea squids in the Aotearoa New Zealand region and is preyed upon by predators such as the sperm whale and orange roughy. However, despite the many publications on M. ingens' diet, knowledge on its feeding ecology remains limited. In this study, we analysed the prey of M. ingens from the Chatham Rise (an ecologically and economically important region east of Te Waipounamu/New Zealand's South Island) using DNA barcoding and otolith identification. Lanternfishes (Myctophidae) were the most frequently encountered prey item, but other teleost species, cephalopods and crustacean fragments were also found, indicating opportunistic and likely cannibalistic feeding behaviour. Five fish species (including a possibly undescribed species of Gymnoscopelus) and Bathyteuthis abyssicola are reported as prey items of M. ingens for the first time. Moroteuthopsis ingens appears to be a component of several dynamic food chains and likely plays an important role in the transfer of carbon throughout marine environments in the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Orienting vertically with the head facing upward allows fish to look for the shadow of their prey against ambient light, while also making their own shadow smaller to predators beneath them. Here, we describe the in situ behavior of three midwater fish in the family Neoscopelidae, Neoscopelus macrolepidotus, Neoscopelus microchir, and Scopelengys tristis, all of which were observed facing vertically with the head downward. This behavior allows the fish to diminish its shadow to hide from predators while hunting prey below. Assessing unique behaviors helps us better understand the role of these and other poorly studied deep-sea fishes. [ABSTRACT FROM AUTHOR]

In the 1950s, the Danish Galathea Expedition undertook one of the first and most comprehensive explorations of our ocean's hadal zone, depths extending from 6,000 to nearly 11,000 m, and presented a rich collection of the diversity of Amphipoda. The subsequent papers, however, concluded that these established 'nothing essentially new' to the existing knowledge of amphipod biology. Since Dahl's foundational paper in 1959, amphipods, primarily from the superfamilies Lysianassoidea and Alicelloidea, emerged as one of the best-sampled hadal fauna, as these mobile invertebrates are readily recovered by different sampling techniques. Importantly, amphipods have become the model taxon, helping us to unlock knowledge about life in the hadal zone. In this review, we collate the knowledge gained since the Galathea Expedition and summarise the current understanding of how amphipods that appear during hadal exploration survive the trench environments. We discuss population structures across depth, inter-trench distribution and connectivity, applications in hadal microbiology, and, critically, how the hadal zone is being impacted by anthropogenic activity. [ABSTRACT FROM AUTHOR]

The article focuses on the potential impacts of ocean-based climate interventions (OBCIs) on deep-sea ecosystems. Topics include discussion on various OBCIs including carbon sequestration, ocean fertilization, ocean alkalinity enhancement, direct injection of liquid CO2 in deep water, and ocean-based technologies for renewable energy; and governance challenges and the need for an integrated research framework to centralize the consideration of deep-sea impacts in mitigation planning.

Caribbean ocean environments house several large deep-sea basins that remain poorly surveyed. Here we report observations of benthic faunal communities attracted to remote, deep-sea video landers deployed at depths between 262 and 1100 m in two deep basins in The Bahamas, the Tongue of the Ocean (n = 18 deployments) and Exuma Sound (n = 11 deployments). The video comprises >8000 min of survey data across five years of sampling (2018–2022). We estimated regional deep-sea particulate organic carbon (POC) flux using satellite-derived observations and a model of POC decay with depth to assess potential food availability to benthic communities living deeper than 800 m in these basins. The benthic POC flux helped to contextualize potential drivers of faunal biodiversity and abundances estimated from the lander measurements. Throughout twilight zone depths of The Bahamas (defined here as approximately 200–1000 m) we identified taxa from 22 families across invertebrates, teleost fishes, and elasmobranchs. Faunal communities were largely dominated by giant isopods (Bathynomus sp.), gulper sharks (Centrophorus sp.), and swimming sea cucumbers (Enypniastes eximia). Despite sampling biases toward larger individuals, our findings suggest that Bahamian twilight zone communities comprise a diversity of large predator species that are potentially sustained through high energetic connectivity with shallow neritic sources of organic carbon. Our findings suggest that the Central and Southern Tongue of the Ocean should be the focus of future sampling efforts given a lack of historical sampling combined with high export productivity to depth. This study provides new insight into community composition, assemblage structure, and POC flux in Caribbean deep-sea ecosystems, shedding light on previously unrecognized patterns of biodiversity. • We surveyed poorly studied Bahamian deep-sea basins using novel landers. • Communities were dominated by large sharks and giant isopods. • Satellite derived POC flux was highly variable across space. • Further work is needed to document cryptic biodiversity in these regions. [ABSTRACT FROM AUTHOR]

I Hidden players - Meiofauna mediate ecosystem effects of anthropogenic disturbances in the ocean i In this chapter, the authors literally leave no stone unturned, examining this topic from every pertinent viewpoint. I Cave meiofauna - Models for ecology and evolution i It seems like sheer academic opulence to actually present an entire chapter devoted to "the often disregarded cave meiofauna" (p. 330), which is a further testament to the intellectual thoroughness of this book. Among the many gems: "The fact that certain meiofauna taxa can carry out nitrate respiration instead of oxic respiration is a fascinating topic" (p. 46). [Extracted from the article]

Orienting vertically with the head facing upward allows fish to look for the shadow of their prey against ambient light, while also making their own shadow smaller to predators beneath them. Here, we describe the in situ behavior of three midwater fish in the family Neoscopelidae, Neoscopelus macrolepidotus, Neoscopelus microchir, and Scopelengys tristis, all of which were observed facing vertically with the head downward. This behavior allows the fish to diminish its shadow to hide from predators while hunting prey below. Assessing unique behaviors helps us better understand the role of these and other poorly studied deep-sea fishes.

Cold seep microbial communities are fascinating ecosystems on Earth which provide unique models for understanding the living strategies in deep-sea distinct environments. In this study, 23 metagenomes were generated from samples collected in the Site-F cold seep field in South China Sea, including the sea water closely above the invertebrate communities, the cold seep fluids, the fluids under the invertebrate communities and the sediment column around the seep vent. By binning tools, we retrieved a total of 768 metagenome assembled genome (MAGs) that were estimated to be >60% complete. Of the MAGs, 61 were estimated to be >90% complete, while an additional 105 were >80% complete. Phylogenomic analysis revealed 597 bacterial and 171 archaeal MAGs, of which nearly all were distantly related to known cultivated isolates. In the 768 MAGs, the abundant Bacteria in phylum level included Proteobacteria, Desulfobacterota, Bacteroidota, Patescibacteria and Chloroflexota, while the abundant Archaea included Asgardarchaeota, Thermoplasmatota, and Thermoproteota. These results provide a dataset available for further interrogation of deep-sea microbial ecology. Measurement(s) metagenome assembled genomes Technology Type(s) metagenome sequencing and genome binning Sample Characteristic - Organism microorganism Sample Characteristic - Environment marine cold seep biome Sample Characteristic - Location South China Sea [ABSTRACT FROM AUTHOR]

The Bay of Biscay is a structurally complex region, exhibiting high biodiversity and productivity and hosting a wide variety of benthic habitats. Unfortunately, current scientific knowledge of deep-sea ecosystems is limited. Our investigation provides an updated vision of the existing knowledge on key aspects of the deep-sea ecosystem and identifies research priorities for the definition of a research roadmap in support of sustainable management, including the protection and conservation of deep-sea ecosystem of the Bay of Biscay. To achieve this, firstly a revision of projects, surveys and studies conducted in the region, was carried out resulting in the identification of 62 publicly available scientific documents. Secondly, an online survey was carried out, receiving 51 responses from 24 research institutions in 9 countries. Finally, a workshop was attended by 39 scientists to identify and discuss ways forward on deep-sea research in the Bay of Biscay. Results indicate that knowledge of benthic habitats, and vulnerable and sensitive habitats/species is good or very good for 45% of the respondents, while limited knowledge was reported for deep pelagic habitats. Almost 75% of the scientists agreed that deep-sea processes affect shallower areas. Funding (71%) and research vessel availability (57%) were considered the most constraining aspects limiting deep-sea research. More than 50% of the scientists perceived a short- or medium-term threat from human activities and pressures, while over than 40% of the respondents considered that there are no, or limited, data available to assess the environmental status. Regarding climate change, 55% of scientists partially or fully agreed with the existence of evidence of climate change effects, but 47% of them totally or partially considered that climate change monitoring is insufficient to assess eventual changes and effects. Most respondents (63%) considered that deep-sea ecosystems are not properly represented in the current Marine Protected Areas network. In terms of future needs, the development of monitoring strategies to reduce costs and guarantee an optimal design, data sharing and an increase in transnational collaboration are most cited. Finally, a proposal for a roadmap to fill in knowledge gaps for a better understating of the ecosystem processes of the deep sea of the Bay of Biscay is delivered. • Scientific knowledge of the deep-sea ecosystem in the Bay of Biscay is limited. • An updated vision of current knowledge on key aspects of the deep-sea ecosystem is provided. • Research priorities for the definition of a research roadmap are identified. • Intended to support sustainable management, protection and conservation. [ABSTRACT FROM AUTHOR]

Aim: Latitudinal and bathymetric species diversity gradients in the deep sea have been identified, but studies have rarely considered these gradients across hard substratum habitats, such as seamount and oceanic island margins. This study aimed to identify whether the current understanding of latitudinal and bathymetric gradients in α‐diversity (species richness) apply to seamount ecosystems, as well as ascertaining whether identifiable trends were present in seamount β‐diversity along a bathymetric gradient. Location: Exclusive Economic Zones of Saint Helena, Ascension Island and Tristan da Cunha, spanning 8–40°S in the South Atlantic. Taxon: Seamount megabenthic communities. Methods: Images from 39 transects, collected between 250 and 950 m, were used to characterise species richness. We subsequently applied general linear models to test possible environmental drivers across latitudinal and bathymetric ranges. Regression models were employed to investigate the β‐diversity gradient of species turnover with depth. Results: Transects in temperate latitude had significantly higher species richness than those in the tropics. Surface primary productivity and substrate hardness both had significant positive effects on species richness, and a weak relationship between temperature and species richness was observed. No significant relationship between species richness and depth was detected, but there was significant species turnover with depth. Main conclusions: Seamounts and oceanic islands do not conform to established depth–diversity relationships within the depth range studied. However, seamounts and oceanic islands in the South Atlantic do appear to follow a parabolic latitudinal diversity gradient, closely associated with higher productivity in temperate regions. [ABSTRACT FROM AUTHOR]

The residence time of fluids circulating through deep‐sea hydrothermal systems influences the extent of water‐rock reactions and the flux of major and minor elements to the ocean. While the fluid residence times in numerous basaltic and gabbroic systems have been determined, those of the less studied ultramafic systems are currently unknown. Fluids that interact with mantle rocks have fundamentally different chemistries and therefore have unique influences on seawater chemistry. In this first investigation of radium isotopes in a serpentinite‐hosted system, vent fluids were discovered to contain 10–100 times greater activities of 223Ra (half‐life = 11.4 days) than observed in high‐temperature basalt‐hosted systems. The 223Ra activities of 10–109 dpm L−1 produce 223Ra/226Ra activity ratios ranging from 9 to 109. These extremely high 223Ra activities, which are accompanied by low activities of 226Ra, place significant constraints on fluid residence times and the adsorption coefficient of radium between fluid and rock. Our data constrain the nondimensional retardation factor (R) to very low values between 1 and 4, reflecting the extent to which Ra is transported more slowly than fluids due to adsorption and other processes. These results suggest that the residence time of fluids in contact with serpentinite is less than 2 y and perhaps as low as 0.5 y. They are surprisingly similar to those of basalt‐hosted systems. Thus, fluids in hydrothermal systems share similar hydrogeological characteristics despite differences in rock types, underlying porosity, and heat sources, enabling larger‐scale models of hydrothermal biogeochemistry to be developed across systems. Plain Language Summary: The well‐known "black smoker" hydrothermal systems occur at ocean spreading centers. High temperature (200°C–400°C) fluids in these systems pass through basalt, where they become both acidic and rich in metals. As they emerge on the seabed after a few years, they precipitate metal‐rich chimneys. Lesser‐known hydrothermal systems occur in serpentinite. These systems form as minerals found deep in the earth are uplifted to the seabed and exposed to seawater. Here chemical reactions at lower temperatures (100°C–200°C) occur that convert primary Fe‐bearing minerals to serpentine, releasing hydrogen (H2) and producing alkaline fluids. These conditions allow simple carbon molecules to be converted to more complex molecules including, potentially, amino acids, without the assistance of living organisms. Once formed, these molecules slowly degrade. A fundamental question regarding serpentinite‐hosted systems is whether the molecules can be exported to the seabed before they are destroyed. We discovered a rare radium isotope, 223Ra (half‐life = 11 days), was much enriched compared to the more common 226Ra (half‐life = 1,600 y) in fluids from the Lost City serpentinite‐hosted system. This argues fluid circulation times of less than 2 y, likely short enough to allow complex molecules to be exported into overlying ocean waters. Key Points: Lost City vent fluids are highly enriched in the short‐lived radium isotope, 223Ra, but not in longer‐lived 226Ra and 228RaRadium adsorption from Lost City vent fluids to solids is very low, similar to basalt‐hosted systemsResidence times of fluids in Lost City serpentinite are constrained to less than 2 y [ABSTRACT FROM AUTHOR]

The ocean is an important inventory of anthropogenic mercury (Hg), yet the history of anthropogenic Hg accumulation in the ocean remains largely unexplored. Deep-sea corals are an emerging archive of past ocean chemistry, which take in sinking or suspended particulate organic matter as their food sources. Such organic matter would exchange Hg with the local seawater before being consumed by the deep, sea corals. As such, the organics preserved in the coral skeleton may record the Hg evolution of the ambient seawater during the time of coral growth. Here, we report the first data on Hg concentrations variability of a deep-sea proteinaceous coral in the oligotrophic North Pacific at the water depth of 1 249 m, in attempt to understand the transfer of anthropogenic Hg into the deep Pacific ocean over the last seven centuries. We find that the Hg concentrations of different coral growth layers have remained relatively constant albeit with considerable short-term variability through time. The overall stable Hg concentration of the last seven centuries recorded in our sample suggests that anthropogenic pollution is not yet a clearly resolvable component in the deep oligotrophic North Pacific waters, in agreement with recent estimation from modelling works and observational studies of modern seawater profiles. As there is hardly an unambiguous way to separate anthropogenic Hg from the natural background based on recent seawater profiles, our historical data provide valuable information helping to understand the oceanic cycle of Hg through time. [ABSTRACT FROM AUTHOR]

A new genus and species of axiid shrimp, Carolinaxius kexuae gen. et sp. nov. is described and illustrated based on a single specimen collected from an unnamed seamount in the Caroline Ridge, northwest Pacific. Although both chelipeds are missing, the specimen can be distinguished from other axiid genera by a combination of characteristics: narrowly triangular rostrum; median carina and lateral gastric carina each with one prominent tooth; submedian gastric carinae converging posteriorly, with teeth; cornea weakly pigmented, eyestalk with acute distomesial tooth on dorsal surface; male pleopod 1 two-articled; pleopod 2 with appendix interna and appendix masculina; pleopods 3–5 with appendix interna. The molecular phylogeny suggests the new genus is most closely related to another recently described genus living inside hexactinellid sponges on seamounts in the Indian Ocean, Montanaxius Dworschak, 2016. However, it differs from Montanaxius in the shape of the rostrum, the arrangement of teeth on the carapace, and the shape of the eyestalk. Besides, the significant molecular differences support the two belonging to different genera. [ABSTRACT FROM AUTHOR]

Three deep-sea black corals belonging to the family Schizopathidae, are reported from two seamounts on the Caroline Ridge in the tropical Western Pacific: Umbellapathes parva sp. nov. with depth of 1 488–1 766 m, Telopathes cf. magna MacIsaac & Best, 2013 with depth of 937–1 016 m, and Stauropathes cf. punctata (Roule, 1905) with depth of 942–1 353 m. The latter two species are the first records in the Western Pacific Ocean. U. parva sp. nov. is characterized by monopodial corallum, relatively long unpinnulated stalk with complex pinnulated branches developing from the lowermost primary pinnules and small spines. It differs from two known congeners by much smaller spines and the present of secondary pinnules. T. cf. magna MacIsaac & Best, 2013 has sparsely branched corallum, relatively long and simple pinnules arranged in subopposite or alternate pairs. S. cf. punctata (Roule, 1905) is characterized by the corallum with almost planar pinnulated branches, and pinnules arranged in subopposite pairs. Our results indicate that the corallum size and shape are variable in conspecific specimens particularly those at different growth stages. By contrast, the size of the polypar spines as well as the abpolypar spines have little variation and can be served as a main differing feature for schizopathid species. The phylogenetic analyses using nuclear internal transcribed spacer region (spanning partial 18S rDNA, ITS1, 5.8S, ITS2, and partial 28S rDNA) and two mitochondrial fragments cox3-IGR-cox1 (COI) and trnW-IGR-nad2 (NAD2) showed Telopathes, Stauropathes, and Bathypathes had close relationships, and Umbellapathes formed a sister clade with Alternatipathes. [ABSTRACT FROM AUTHOR]

Seamount is a unique deep-sea ecosystem widely distributed in the world. Its biodiversity is vibrant due to its specific geographical and hydrological conditions. However, the diversity and features of foraminifera in such an environment have rarely been studied. We extracted environmental DNA (eDNA) in sediments and amplified the partial small subunit ribosomal DNA (SSU rDNA) of foraminifera to understand the foraminiferal diversity from four sites in Magellan Seamount (Western Pacific Ocean). Partial SSU rDNA sequencing was conducted and 912 979 foraminiferal reads were obtained and gathered into 266 operational taxonomic units (OTUs). In the available dataset, a high proportion of rare OTUs and low identity OTUs in each studied sample showed that the Magellan Seamount foraminiferal community might have a high genetic novelty. The relative abundance of foraminifera varied between replicates probably due to the existence of bias in amplification process and patchiness of the deep-sea floor. It showed that the Magellan Seamount has a relatively high benthic foraminiferal diversity characterized mainly by monothalamiids (76.37% of total reads) in association with rotaliids (19.03% of total reads), including planktic foraminiferal sequences (38.58% of rotaliids; 7.36% of total reads). The remaining reads were assigned to miliolids (0.83% of total reads) and textulariids (0.66% of total reads), and 3.11% of total reads are unassigned to a specific family. The comparative analysis with foraminiferal assemblages from coastal and deep-sea environments indicated that seamounts could aggregate species from a nearby deep-sea. [ABSTRACT FROM AUTHOR]

Laetmonice Kinberg, 1856 is a remarkable genus characterized by having harpoon notochaetae in the polychaete family Aphroditidae. We describe a new species of Laetmonice, Laetmonice iocasica sp. nov., found from seamounts on the Caroline Ridge in the tropical Western Pacific. The new species is readily distinguished from congeners, particularly those distributed in the Indo-Pacific Ocean by possessing 45 segments with 18 pairs of elytra, and the tuberculated harpoon notochaetae in the elytrigerous segments, which are replaced by tuberculated notochaetae without recurved fangs on segments 4 and 5. Laetmonice iocasica sp. nov. is closely related to L. producta Grube, 1877, but differs in both morphology and the genetic distance of the mitochondrial cytochrome oxidase subunit I (COI) sequences. Laetmonice producta Grube, 1877 contained five varieties reported in various marine areas, which have been raised to species level. However, the records of L. producta from the Sagami Bay and Suruga Bay in Japan and in the south-eastern Australia remain obscure and probably represent a different species. The data indicate that L. producta, which was originally described from Kerguelen Islands in the Southern Ocean and later commonly found on the Antarctic shelf, is probably distributed only at high latitudes of the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Deep‐sea sponge grounds are hotspots of benthic biomass and diversity. To date, very limited data exist on the range of environmental conditions in areas containing deep‐sea sponge grounds and which factors are driving their distribution and sustenance. We investigated oceanographic conditions at a deep‐sea sponge ground located on an Arctic Mid‐Ocean Ridge seamount. Hydrodynamic measurements were performed along Conductivity‐Temperature‐Depth transects, and a lander was deployed within the sponge ground that recorded near‐bottom physical properties as well as vertical fluxes of organic matter over an annual cycle. The data demonstrate that the sponge ground is found at water temperatures of −0.5°C to 1°C and is situated at the interface between two water masses at only 0.7° equatorward of the turning point latitude of semi‐diurnal lunar internal tides. Internal waves supported by vertical density stratification interact with the seamount topography and produce turbulent mixing as well as resuspension of organic matter with temporarily very high current speeds up to 0.72 m s−1. The vertical movement of the water column delivers food and nutrients from water layers above and below toward the sponge ground. Highest organic carbon flux was observed during the summer phytoplankton bloom period, providing fresh organic matter from the surface. The flux of fresh organic matter is unlikely to sustain the carbon demand of this ecosystem. Therefore, the availability of bacteria, nutrients, and dissolved and particulate matter, delivered by tidally forced internal wave turbulence and transport by horizontal mean flows, likely plays an important role in meeting ecosystem‐level food requirements. Plain Language Summary: Sponge grounds are important ecosystems in the deep‐sea that can be compared to tropical reefs. To date, very limited data exist on the range of environmental conditions in areas where deep‐sea sponges and their accompanying fauna are found. In this study, we investigated environmental conditions at a deep‐sea sponge ground located on the summit of an Arctic seamount. Measurements of the water around the seamount and close to the sponge ground were performed recording near‐bottom physical properties as well as the food supply over an annual cycle. At the summit of the seamount, the water flow interacts with the seamount itself, which produces turbulent mixing with temporarily high current speeds. At the same time, water movements around the seamount deliver food and nutrients from water layers above and below toward the sponge ground. Fresh food from the surface water was delivered only during one major event in the summer phytoplankton bloom period. The amount of food sinking from the surface is unlikely to sustain the energetic demands of this ecosystem. Therefore, the availability of other food resources such as bacteria, dissolved and particulate matter and their delivery by water movements likely play an important role in meeting ecosystem‐level food requirements. Key Points: Long‐term study at a deep‐sea sponge ground provides environmental ranges known to support spongesHydrodynamic processes deliver water with different beneficial characteristics from above and below toward the sponge groundBenthic organisms receive only a small amount of food sinking from the surface waters, which is likely not sustaining their energy demand [ABSTRACT FROM AUTHOR]

A novel species of the family Alepocephalidae (slickheads), Narcetes shonanmaruae, is described based on four specimens collected at depths greater than 2171 m in Suruga Bay, Japan. Compared to other alepocephalids, this species is colossal (reaching ca. 140 cm in total length and 25 kg in body weight) and possesses a unique combination of morphological characters comprising anal fin entirely behind the dorsal fin, multiserial teeth on jaws, more scale rows than congeners, precaudal vertebrae less than 30, seven branchiostegal rays, two epurals, and head smaller than those of relatives. Mitogenomic analyses also support the novelty of this large deep-sea slickhead. Although most slickheads are benthopelagic or mesopelagic feeders of gelatinous zooplankton, behavioural observations and dietary analyses indicate that the new species is piscivorous. In addition, a stable nitrogen isotope analysis of specific amino acids showed that N. shonanmaruae occupies one of the highest trophic positions reported from marine environments to date. Video footage recorded using a baited camera deployed at a depth of 2572 m in Suruga Bay revealed the active swimming behaviour of this slickhead. The scavenging ability and broad gape of N. shonanmaruae might be correlated with its colossal body size and relatively high trophic position. [ABSTRACT FROM AUTHOR]

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 analyses 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. Consequently, spatial point process analyses (SPPA) and Bayesian network inference (BNI) can be used to reveal key insights into the ecological dynamics of these deep-sea communities. Here we use these analyses to investigate the ecology of deep-sea glass sponge dominated community “The Forest of the Weird” (2,442 m 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: Farreidae Aspidoscopulia sp. and Euplectellidae Advhena magnifica with octocorals Narella bowersi, Narella macrocalyx, and Rhodaniridogorgia also present in large proportions. SPPA of the dead vs. alive organisms revealed a random distribution of dead amongst the living, showing a non-density dependent cause of death for the majority of taxa. However, in the high-density ridge crest region there was non-random aggregation of dead specimens, revealing density-dependent mortality for Aspidoscopulia. SPPA showed that the glass sponges and octocorals were each 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. BNI found that mutual habitat associations between different taxa resulted in inter-specific competition at larger (2–4 m) spatial scales, with instances of competition at small-spatial scales (

Deep-sea organisms survive in an extremely harsh environment. There must be some genetic adaptation mechanisms for them. We systematically characterized and compared the complete mitochondrial genome (mitogenome) of a deep-sea crab (Chaceon granulates) with those of shallow crabs. The mitogenome of the crab was 16 126 bp in length, and encoded 37 genes as most of a metazoan mitogenome, including 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, and 2 ribosomal RNA (rRNA) genes. The gene arrangement and orientation was conserved in the crabs. However, a unique mitogenome element regulator, the origin of light-strand replication (OL), was firstly predicted in the present crab mitogenome. In addition, further positive selection analysis showed that two residues (33S in ND3 and 502I in ND5) in C. granulates mitogenome were positively selected, indicated the selective evolution of the deep-sea crab. Therefore, the mitogenome of deep-sea C. granulates showed a unique OL element and positive selection. These special features would influence the mitochondrial energy metabolism, and be involved in the adaptation of deep-sea environment, such as oxygen deficits and low temperatures. [ABSTRACT FROM AUTHOR]

Kaikōura Canyon, offshore Aotearoa/New Zealand, is a hotspot for deep-sea benthic biology with globally high faunal abundance. The M w 7.8 Kaikōura earthquake in 2016 triggered a severe disturbance that reshaped the canyon, evacuating an estimated 850 metric megatonnes of sedimentary material down canyon. The Kaikōura Canyon habitat is now recovering from this removal of both seafloor substrate and associated organisms. We measured post-event benthic macrofauna density together with biomass and sediment properties and related these to infaunal bioturbation activity, sediment community oxygen consumption (SCOC) and associated benthic macronutrient biogeochemical fluxes. Three legacy sites were used as reference along a depth transect of the canyon axis at 917, 1249, and 1480 m water depths. We found distinct differences in benthic functioning between sites. While many parameters measured followed the expected relationships of decreasing with depth some benthic biological activity metrics did not. Our data suggests that the sites differ based on the relative impact and type of disturbance experienced during the earthquake-triggered, canyon-flushing event. We find SCOC was linked to bioturbatory behaviour and sediment organic matter content, rather than taxa density or biomass. While the greatest bioturbation activity was measured at the shallowest site, the greatest SCOC was measured at the middle depth site due to elevated sediment organic matter content. These observations provide a wider benchmark for infaunal bioturbation and faunal-mediated biogeochemical processes in deep-sea canyon environments and provide rare insights of recovery trajectories for deep-sea benthic communities and ecosystem function after large seafloor disturbances. • Post-event canyon benthic community abundance and function metrics decrease with depth for most parameters quantified. • Higher than expected sediment community oxygen consumption (SCOC) was measured at the middle depth site. • SCOC in the canyon is relatively high co mpared to other comparable Pacific deep-sea locations. • SCOC was linked to bioturbatory behaviour and sediment organic matter content, rather than faunal abundance or biomass. [ABSTRACT FROM AUTHOR]

The Persimmon Eelpout (Eucryphycus californicus) is a relatively unknown, deep-sea fish inhabiting temperate marine waters on the west coast of North America. Using samples collected in the mid-1970s, the most recent targeted sampling for this species, we present basic life history attributes, and an analysis of the relationship between E. californicus and drift macrophyte habitat in the Monterey Canyon, California, USA. A diet analysis revealed that the fish consumes predominantly small crustaceans, especially amphipods and copepods, including species that associate with drift macrophyte habitat. Otoliths were analyzed to yield age estimates ranging from 0 to 6 years, and growth was modeled showing a maximum length of 203 mm for males and 271 mm for females. An analysis of the reproductive ecology of E. californicus showed that like many deep-sea fishes, females lay relatively few, large eggs. The species exhibits a protracted spawning period, and females spawn with only one functional ovary. Empirical information presented in this paper and anecdotal evidence shows that E. californicus likely relies on drift algae and seagrasses, a habitat subsidy exported to the deep-sea environment from adjacent kelp forest ecosystems, for shelter and to concentrate food resources. This example of a species dependent on an ecosystem subsidy adds to our knowledge regarding the effects of cross-ecosystem connectivity in the marine environment, and furthers our understanding of the ecology of the deep-sea macrofaunal assemblage in Monterey Bay. [ABSTRACT FROM AUTHOR]