Deep-sea Habitats Research Articles

Estimating preferences for Mediterranean deep-sea ecosystem services: A discrete choice experiment

The deep sea represents Earth’s largest (but least explored) biome. It is increasingly affected by anthropogenic stressors and climate change, which threaten the provision of essential ecosystem services. The monetary value of these benefits has rarely been assessed. High biodiversity is hosted in the deep sea and, more generally, in the oceans. This paper uses a hypothetical choice experiment to investigate Italian households’ preferences for deep-sea ecosystem services. The data show wide heterogeneity of the preferences for preserving the Mediterranean deep sea. Many respondents indicate that they would refuse to pay to support the protection of biodiversity and scientific research in this remote and unfamiliar environment. Overall, global warming was of little concern for most respondents, who would not be willing to pay to limit the increase in global temperatures. High income and formal education positively influenced the willingness of the respondents to donate to Non-Governmental Organization’s initiatives to support the Mediterranean deep sea. Deep-water corals appear more ‘charismatic’ to respondents than submarine canyons among deep-sea habitats.

Healthy thalli of the invasive seaweed Rugulopteryx okamurae (Phaeophyceae) being massively dragged into deep-sea bottoms by the Mediterranean Outflow Water

ABSTRACT The invasive seaweed Rugulopteryx okamurae has recently arrived in Europe from the western Pacific. Its explosive spread on coastal areas of the Gulf of Cádiz (GoC), Strait of Gibraltar and Alboran Sea is spoiling native coastal ecosystems and inflicting heavy losses on ecosystem services. We discovered for the first time large amounts (up to 17 g m–2) of detached R. okamurae thalli on deep-sea bottoms of the GoC that are being dragged from the Strait of Gibraltar shores into the NE Atlantic by the Mediterranean Outflow Water (MOW). Laboratory experiments revealed that collected unattached macroalgae from deep-sea locations were alive and healthy and maintained intact photosynthetic capacity after long dark periods, suggesting a tremendous resilience and invasive potential. Given the rapid transport of healthy thalli by the MOW and massive accumulation of them in the GoC basin, R. okamurae could represent a major threat to NE Atlantic ecosystems, affecting not only coastal but also deep-sea habitats.

Mapping marine ecosystem services potential across an oceanic archipelago: Applicability and limitations for decision-making

Understanding the multiple benefits (i.e. Ecosystem Services, ES) that marine habitats provide to society is key for adequate decision-making that maintains our well-being in the long-term. The main objective of this research was to map and assess, in the context of marine spatial planning, the ES supply of shallow and deep-sea habitats in the Canary Islands across biological zones and substrate types. An ES-matrix was developed through a literature review to evaluate the supply potential, complemented with the habitats’ total extension to assess the supply capacity of each resulting ES. The matrix linked 34 habitats in relation to 42 ES, over ca. 485,000 km2. Cultural ES were the most abundant in the archipelago. On average, shallow habitats supplied potentially 25 ES compared to 17 ES by deep-sea habitats. This is likely to be explained by limitations regarding the available information suggesting that both provisioning ES and ES supply potential of the deep-sea were underestimated. The supply capacity analysis showed that particularly certain regulating and maintenance services may be at risk in the face of habitat degradation. Results enabled the extrapolation of already existing ES monetization, e.g. for those accounted for Cymodocea nodosa generating 25,633,919 € y-1 in the Canary Islands. This study provided the first comprehensive spatial assessment of ES supply potential in the Canary Islands, filling a regional knowledge gap. This enables accounting for previously overlooked ES in the region, strengthening the idea that coastal communities’ well-being in small islands depends on their marine ecosystems. Finally, results were discussed in relation to their applicability and limitations to marine spatial planning and protected area design informing on the potentially large societal benefits that may be at risk when allocating maritime activities spatially.

Facies created by the yellow coral Dendrophyllia cornigera (Lamarck, 1816): Origin, substrate preferences and habitat complexity

The yellow coral Dendrophyllia cornigera (Lamarck, 1816) is a NE Atlantic-Mediterranean scleractinian. It is considered a typical hard bottom species, generally reported on outcropping rocks from mesophotic to upper bathyal depths. Several evidences suggest that this species is able to tolerate a broad range of temperatures, which allows it to colonize numerous environments in a wide depth range.In the present study, we first provided a detailed ecological characterization of the D. cornigera dense aggregation thriving on the Mantice Shoal (NW Ligurian Sea, Mediterranean Sea). Information on substrate type and inclination, average extension and density, colonies size-class frequency distribution and associated fauna are reported. Then, we presented an extensive review of the available information on the ecology of this species, including 142 new ROV records from the Italian coast (40–1820 m). Results indicated that D. cornigera occurs on a wide range of substrates, including soft bottoms and hardgrounds (outcropping rocks, coralligenous rock and dead cold-water coral frameworks), with significant differences in colony density and size among different substrates.Dendrophyllia cornigera creates three main facies, each characterized by a specific combination of substrate, inclination, depth, and associated fauna. Scattered living colonies, as well as large thanatocoenoses, display a wide geographical and bathymetric distribution. Differently, the facies represented by dense meadows on horizontal soft-bottoms results rare, being reported only from the Mantice Shoal and the Amendolara Bank (Ionian Sea). The radiocarbon age of the thanatocoenoses varies between 400 (Corsica Channel) and 13000 (Vercelli Seamount) years before present.This study highlights the wide adaptability of D. cornigera in terms of environmental settings, changing the current view on the ecology of this species and providing essential insights for the implementation of international deep-sea habitat classification schemes and conservation measures.

Rock outcrops enhance abyssal benthic biodiversity

Abyssal polymetallic nodule fields represent a unique deep-sea habitat. The hard substratum provided by nodules is thought to increase habitat complexity, promoting the occurrence of highly diverse abyssal assemblages. However, hard substratum in these habitats is also available as outcropping rock fragments, but their contribution to habitat heterogeneity has been largely overlooked. Here, we assessed if the type and size of hard substratum can modulate benthic biodiversity at local scales within the Clarion Clipperton Zone (N Pacific abyss). We compared megafauna (animals >10 mm) assemblages in nodule bearing habitats with those in areas containing rocks in addition to nodules. We found a lower faunal density but a clearly higher diversity and more heterogenous composition in the assemblages of rock bearing areas compared to those with only nodules. In addition, hard substratum patch size appeared to positively influence the size of some taxa, like bamboo corals. These results suggest that rocks, in addition to nodules, constitute keystone structures enhancing habitat heterogeneity at local scales within nodule fields. Rock areas appear common in some abyssal plains and may make regionally-important contributions to abyssal biodiversity, suggesting that they may be relevant to include in conservation efforts.

Head anatomy of a lantern shark wet-collection specimen (Chondrichthyes: Etmopteridae).

In this study, we apply a two-step (untreated and soft tissue stained) diffusible iodine-based contrast-enhanced micro-computed tomography array to a wet-collection Lantern Shark specimen of Etmopterus lucifer. The focus of our scanning approach is the head anatomy. The unstained CT data allow the imaging of mineralized (skeletal) tissue, while results for soft tissue were achieved after staining for 120 h in a 1% ethanolic iodine solution. Three-dimensional visualization after the segmentation of hard as well as soft tissue reveals new details of tissue organization and allows us to draw conclusions on the significance of organs in their function. Outstanding are the ampullae of Lorenzini for electroreception, which appear as the dominant sense along with the olfactory system. Corresponding brain areas of these sensory organs are significantly enlarged as well and likely reflect adaptations to the lantern sharks' deep-sea habitat. While electroreception supports the capture of living prey, the enlarged olfactory system can guide the scavenging of these opportunistic feeders. Compared to other approaches based on the manual dissection of similar species, CT scanning is superior in some but not all aspects. For example, fenestrae of the cranial nerves within the chondrocranium cannot be identified reflecting the limitations of the method, however, CT scanning is less invasive, and the staining is mostly reversible and can be rinsed out.

Gene loss and symbiont switching during adaptation to the deep sea in a globally distributed symbiosis

Chemosynthetic symbioses between bacteria and invertebrates occur worldwide from coastal sediments to the deep sea. Most host groups are restricted to either shallow or deep waters. In contrast, Lucinidae, the most species-rich family of chemosymbiotic invertebrates, has both shallow- and deep-sea representatives. Multiple lucinid species have independently colonized the deep sea, which provides a unique framework for understanding the role microbial symbionts play in evolutionary transitions between shallow and deep waters. Lucinids acquire their symbionts from their surroundings during early development, which may allow them to flexibly acquire symbionts that are adapted to local environments. Via metagenomic analyses of museum and other samples collected over decades, we investigated the biodiversity and metabolic capabilities of the symbionts of 22 mostly deep-water lucinid species. We aimed to test the theory that the symbiont played a role in adaptation to life in deep-sea habitats. We identified 16 symbiont species, mostly within the previously described genus Ca. Thiodiazotropha. Most genomic functions were shared by both shallow-water and deep-sea Ca. Thiodiazotropha, though nitrogen fixation was exclusive to shallow-water species. We discovered multiple cases of symbiont switching near deep-sea hydrothermal vents and cold seeps, where distantly related hosts convergently acquired novel symbionts from a different bacterial order. Finally, analyses of selection revealed consistently stronger purifying selection on symbiont genomes in two extreme habitats - hydrothermal vents and an oxygen-minimum zone. Our findings reveal that shifts in symbiont metabolic capability and, in some cases, acquisition of a novel symbiont accompanied adaptation of lucinids to challenging deep-sea habitats.

Significant Differences in Planktonic Virus Communities Between "Cellular Fraction" (0.22 ~ 3.0µm) and "Viral Fraction" (< 0.22μm) in the Ocean.

Compared to free-living viruses (< 0.22m) in the ocean, planktonic viruses in the "cellular fraction" (0.22 ~ 3.0μm) are now far less well understood, and the differences between them remain largely unexplored. Here, we revealed that even in the same seawater samples, the "cellular fraction" comprised significantly distinct virus communities from the free virioplankton, with only 13.87% overlap in viral contigs at the species level. Compared to the viral genomes deposited in NCBI RefSeq database, 99% of the assembled viral genomes in the "cellular fraction" represented novel genera. Notably, the assembled (near-) complete viral genomes within the "cellular fraction" were significantly larger than that in the "viral fraction," and the "cellular fraction" contained three times more species of giant viruses or jumbo phages with genomes > 200kb than the "viral fraction." The longest complete genomes of jumbo phage (~ 252kb) and giant virus (~ 716kb) were both detected only in the "cellular fraction." Moreover, a relatively higher proportion of proviruses were predicted within the "cellular fraction" than "viral fraction." Besides the substantial divergence in viral community structure, the different fractions also contained their unique viral auxiliary metabolic genes; e.g., those potentially participating in inorganic carbon fixation in deep sea were detected only in the "cellular-fraction" viromes. In addition, there was a considerable divergence in the community structure of both "cellular fraction" and "viral fraction" viromes between the surface and deep-sea habitats, suggesting that they might have similar environmental adaptation properties. The findings deepen our understanding of the complexity of viral community structure and function in the ocean.

The Diversity of Deep-Sea Actinobacteria and Their Natural Products: An Epitome of Curiosity and Drug Discovery

Bioprospecting of novel antibiotics has been the conventional norm of research fostered by researchers worldwide to combat drug resistance. With the exhaustion of incessant leads, the search for new chemical entities moves into uncharted territories such as the deep sea. The deep sea is a furthermost ecosystem with much untapped biodiversity thriving under extreme conditions. Accordingly, it also encompasses a vast pool of ancient natural products. Actinobacteria are frequently regarded as the bacteria of research interest due to their inherent antibiotic-producing capabilities. These interesting groups of bacteria occupy diverse ecological habitats including a multitude of different deep-sea habitats. In this review, we provide a recent update on the novel species and compounds of actinomycetes from the deep-sea environments within a period of 2016–2022. Within this period, a total of 24 new species of actinomycetes were discovered and characterized as well as 101 new compounds of various biological activities. The microbial communities of various deep-sea ecosystems are the emerging frontiers of bioprospecting.

First record of the family Caprellidae (Amphipoda: Senticaudata) from the abyssal zone of the Bering Sea with description of a new species of Cercops

Three species of the amphipod family Caprellidae were collected in the area of the submarine Piip Volcano, the northwestern Bering Sea, during 75-th and 82-nd research cruises aboard the R/V Akademik M.A. Lavrentyev in 2016 and 2018 using the ROV Comanche-18. Two morphospecies of the genus Caprella (Caprellinae) were found on the Northern Summit of the Piip Volcano (depth 373 m) and on its northern slope (749–986 m). A new species, Cercops caecus Kireev and Golovan sp. nov. (Paracercopinae), was sampled in the abyssal zone adjacent to its southern slope (3362 m), where it was found on hydroids growing on a hexactinellid sponge. The new species differs from all other species of the genus by the lack of eyes and the presence of two pairs of gills in contrast to three paired gills found in the other congeners. This is the first record of an abyssal species of the subfamily Paracercopinae, whose other representatives are known from the shelf and the upper bathyal zones of the North Pacific, Arctic, and North Atlantic. This finding demonstrates the parallel processes of colonization of deep-sea habitats occurring in different subfamilies of Caprellidae. An updated diagnosis and a key to the Cercops species are provided. For the first time for Paracercopinae, data on the molecular marker (18S rRNA) was obtained.

Habitat utilization, demography, and behavioral observations of the squat lobster, Eumunida picta (Crustacea: Anomura: Eumunididae), on western North Atlantic deep-water coral habitats

Deep-sea coral habitats, comprising mostly Lophelia pertusa (Linnaeus 1758), are well developed on the upper and middle continental slope off the southeastern United States (SEUS). These habitats support a diverse and abundant invertebrate fauna, yet ecology and biology of most of these species are poorly known. Ten cruises conducted off the SEUS (Summer–Fall; Cape Lookout, NC–Cape Canaveral, FL) from 2000 to 2005, and in 2009 provided an opportunity to investigate abundance and distribution of Eumunida picta Smith1883, a large-sized species of squat lobster commonly associated with these deep-water coral habitats. Video analysis from 70 manned-submersible dives documented occurrence, density, location on the coral colony, and behavioral observations for 5774 individuals of E. picta. Individuals collected (n = 178) from coral and adjacent habitats (e.g., rubble, soft sediments) were measured and their sex determined. Males and females were comparable in size (to 53.5 mm carapace length) and exhibited a sex ratio of approximately 1:1. Eumunida picta were most frequently observed as solitary individuals on high-profile coral matrix and were noted only infrequently on coral rubble, or rarely on soft substratum. Presence of coral habitat (i.e., live/dead L. pertusa), geographic region within the sampling area, and depth significantly influenced abundances of E. picta. Additionally, coral habitat (dead versus live coral), vertical position on the coral (upper, middle, or lower zone), as well as horizontal position in relation to the coral matrix (outer surface versus embedded in coral matrix) were significant factors influencing E. picta distributions within the coral habitat. More individuals were found on dead versus live coral, and most frequently occurred on the outer surfaces of coral branches located on the upper portion or near the tops of coral colonies. Eumunida picta were most often observed with claws extended into the water column. This unique hunting stance provides this squat lobster the opportunity to capture prey from the water column. An active predator, this species utilizes both pelagic (i.e., fishes, pyrosomes) and benthic (e.g., scavenging and grazing) food resources, and may function as an important trophic link between the water column and the benthos. Although considered a facultative reef associate in the strictest sense of the term, E. picta has a complex and intimate relationship with L. pertusa. Based on observations from dive videos, E. picta is a dominant and ecologically important member of the invertebrate assemblage associated with deep-sea coral habitats off the SEUS. As such, this species figures prominently in the structure and function of this ecosystem.

New species of Ophryotrocha (Annelida: Dorvilleidae) associated with deep-sea reducing habitats in the Bering Sea, Northwest Pacific

Four species of Ophryotrocha (Annelida, Dorvilleidae) from deep-sea reducing habitats (methane seeps on the Koryak slope and hydrothermal vents of the submarine Piip Volcano) were collected in the western part of the Bering Sea, NW Pacific. Descriptions of two of these new Ophryotrocha species, namely O. beringiana sp. nov. and O. seepens sp. nov., confirmed with molecular analyses, are presented herein. The detailed descriptions with electron microscopy illustrations for the new species are presented and their differences from similar species are discussed. In addition to the morphological description, the phylogenetic relationships of the new dorvilleids are provided using two nuclear (18S RNA, histone H3) and two mitochondrial (16S RNA and cytochrome c oxidase subunit 1, COI) markers in an analysis containing 54 terminal taxa. Phylogenetic analyses using MrBayes and Maximum Likelihood analyses show that O. beringiana sp. nov. and O. seepens sp. nov. are sister species, and together with O. platykephale, O. globopalpata and O. flabella form a subclade of deep-sea Pacific species within a clade referred to here as ‘globopalpata–platykephale’. In our molecular analysis, the clade currently consists of ten species, nine of those (except for O. longidentata, the only shallow Atlantic species not reported in chemosynthetic habitats) have been described from Pacific deep-sea reducing environments (hydrothermal vents, cold methane seeps, whale-falls). The ecology and geographic distribution of the reported species are discussed.

Using habitat classification and large-scale spatial planning model to identify environmental areas: A case study in the area of the Northwest Pacific Ocean

The deep sea refers to the parts of the oceans with a depth of more than 200 m, and it comprises the largest habitat on earth with the most abundant and diverse marine life. Human activities, such as deep-sea mining, fishing, and shipping, can have severe impacts on deep-sea species and habitats. With the development of the related equipment and technology, interest in deep-sea mining continues to rise; therefore, protecting the unique and fragile deep-sea marine ecosystem has become a global focus. Given the fragility of the deep-sea habitats and the growing demand for deep-sea resources, the United Nations established the International Seabed Authority (the ISA) in 1972, which represents everyone worldwide, to manage the mineral resources in the international seabed area (also known as “the Area”) while fulfilling environmental protection obligations. The most important objective of the regional environmental management plan (REMP) in the Area initiated by the ISA is to balance deep-sea mining and environment protection, and the ISA has considered numerous types of area-based management tools (ABMTs) in the development of the REMPs (Table 1). Using the different ABMTs, several key environmental areas or sites have been identified in various regions, such as the areas of particular environmental interest (APEIs), sites in need of protection (SINPs), or areas in need of protection (AINPs). Additionally, deep-sea mining is prohibited in these sites/areas to avoid its irrecoverable impact on the environment in the Area. The designation these environmental areas or sites can improve the function and resilience of the ecosystem and avoid the unrecoverable impact of deep-sea mining. In this study, we selected the international areas of the Northwest Pacific Ocean for a case study. In order to protect representative species and habitats, such as cold-water corals and seamounts, we utilized environmental factors to classify the study area into eight types of habitats. We then used the appropriate criteria to identify candidate AINPs in two scenarios with a large-scale spatial planning model and analyzed the differences in the protected proportion of the eight types of habitats. The results indicate that identifying the candidate AINPs can reach the protection target of approximately 30% of the area, and each representative species and habitat can be protected. The results obtained in this study can provide technical references for the implementation of REMPs and the designation of AINPs in the study area.

Unveiling deep-sea habitats of the Southern Ocean-facing submarine canyons of southwestern Australia

Here we present the outcomes of the first deep-sea remotely operated vehicle study of previously unexplored submarine canyon systems along the southwest Australian continental margin. This was conducted around: (1) the Bremer Marine Park; (2) the Mount Gabi seamount and nearby slope-shelf margin at the interface of the Southern and Indian oceans; with new information from (3) the Perth Canyon Marine Park located in the SE Indian Ocean. These canyons differ from many explored around the world in having no connectivity to continental river systems, thus little detrital input, with the Bremer systems and Mount Gabi facing the Southern Ocean which plays a key role in the global ocean circulation and climate systems. Such studies in the vast deep waters around the Australian continent are rare given the lack of local ROV capability available for research, thus little is known about these environments.Using the resources of the Schmidt Ocean Institute, we characterised the submarine topography from high-resolution bathymetric mapping, geology, physical and chemical oceanography, and provide an overview of these environments including the fauna observed and collected. We show that these Southern Ocean-influenced environments incorporate South Indian Central Water, Subantarctic Mode Water, Antarctic Intermediate Water, and Upper and Lower Circumpolar Deep Water, with Antarctic Bottom Water present in deep water just south of the Bremer canyon systems. The richness in megabenthos, especially along the steep, rocky substrates of the canyon heads and walls around the Bremer canyon systems, contrasts to the comparatively depauperate fauna of the more northerly Perth Canyon. Various corals serve as important substrates for a range of other species and often exhibit particular faunal associations. Especially notable are distinct ecological zones including a bryozoan and sponge-dominated (animal) forest on the shelf edge, spectacular coral gardens along canyon margins, and the occurrence of solitary scleractinians well below the aragonite saturation horizon. Subfossil coral deposits were discovered across all three study areas, reflecting periodic waxing and waning of deep-water Scleractinia throughout this southwest region. Extensive pre-modern assemblages at Mount Gabi contrast markedly with the sparse populations of living species and suggest that it might have once been a major coral hotspot, or whether they reflect long-term coral aggregations is yet to be determined. Nevertheless, stark differences in both living and past coral distribution patterns across our study sites point to at least localised fluctuations in Southern Ocean-derived nutrient and/or oxygen supplies to these deep-sea communities.

Phylogenetic placement, morphology and gill-associated bacteria of a new genus and species of deep-sea mussel (Mytilidae: Bathymodiolinae) from the South China Sea

Mussels in the subfamily Bathymodiolinae are common inhabitants of deep-sea chemosynthetic habitats, but in many places their diversity remains unknown. Here we describe Nypamodiolus samadiae n. gen. et n. sp. (Mytilidae: Bathymodiolinae) based on samples collected from the Haima cold seep in the South China Sea. Phylogenetic analyses based on fragments of three mitochondrial (cox1, 16S rRNA and nad4) and three nuclear (18S rRNA, 28S rRNA and histone H3) genes show that this new species belongs to a new genus, Nypamodiolus, which includes three named species (Myrina longissima Thiele and Jaeckel, 1931, Myrina simpsoni Marshall, 1900, Idasola japonica Habe, 1976) and a few undescribed species. Nypamodiolus n. gen. is characterized by small-sized, modioliform to fan-shaped shells with the umbones in a non-terminal position, and by robust anterior and posterior byssal retractor muscles arranged in roughly one plane. Most closely related to Nypamodiolus samadiae n. sp. is an undescribed species from the northern Papua New Guinea, to which it has a Kimura-2-parameter genetic distance of 11.8% for cox1. Sequencing the V3–V4 region of the microbial 16S rRNA gene reveals two dominant gill-associated bacteria in the new species, including one sulfur-oxidizing Gammaproteobacteria (relative abundance: 43.8–58.8%) and one unclassified Spirochaetes (relative abundance: 23.9–28.1%). Morphologically, N. samadiae n. sp. is similar to N. simpsoni, while can be distinguished by a larger maximum shell size (45.0 mm vs. 40.0 mm), larger length/height ratio (2.6–2.9 vs. 2.1–2.4), broader posterior end, slightly curved dorsal margin, and more anterior umbones.

Improving knowledge of Funiculina quadrangularis and vulnerable marine ecosystems in the south Adriatic

The Adriatic Sea is one of the most exploited areas in the Mediterranean; however, a large part of the South Adriatic Sea remains largely unexplored. Unfortunately, direct and indirect anthropogenic impacts are increasing exponentially, causing a loss of flagship species and threatening ecosystem functioning. This has led to several international conventions demanding better protection and management of sensitive species and areas worldwide. Soft mud facies bearing the sea pen Funiculina quadrangularis are indicators of vulnerable marine ecosystems (VMEs). This study aimed a) to contribute to the knowledge on the distributions of F. quadrangularis and VMEs, and b) to assess the main threats, thus enabling better identification of areas that need protection and ecosystem base management. The results show that F. quadrangularis are distributed from 160 m to 400 m depth, with the highest population density of 0.83 colony/m2 reported in the Adriatic Sea at a 162 m depth. However, using video ground truthing, we registered stresses on deep-sea habitats originating from fishery and marine litter. Further research is needed to ascertain other potentially vulnerable areas. Moreover, international discussion is needed to determine future steps for the protection and sustainable use of resources beyond national jurisdictions.

Evaluating deep-sea communities' susceptibility to mining plumes using shallow-water data

Increased suspended sediment concentrations (SSC) are a major stressor across aquatic habitats. Here, the literature was synthesized to show that animal responses to increases in relative SSC (test concentration/natural background concentration) were similar in type and negative across different shallow-water (marine, estuarine, freshwater) habitats. Further, animal sensitivities are similar across habitats based on relative SSC and occur starting at low relative SSC increases in all habitats despite differences in natural background SSC. Based upon these similarities in relative SSC sensitivities, deep-sea sensitivity values for acute exposure to increased SSC, where empirical data are almost non-existent, were estimated. Because of the low natural SSC in deep sea environments, very small increases in absolute SSC could result in acute effects. How the methods and results can be used to inform regulatory thresholds are discussed. Because of the large variability in shallow water datasets and differences between deep-sea and shallow-water habitats, deep-sea specific data are needed to verify the estimates and improve their precision. Following the precautionary principle and the results presented here, it is recommended that the threshold for acute plume impacts is set very close to natural background levels.

Development of microsatellites markers for the deep coral Madracis myriaster (Pocilloporidae: Anthozoa)

In 2013 Colombia made an important step towards the construction and management of Marine Protected Areas (MPAs) by establishing the first Deep Corals National Park (PNNCP). Inside this MPA, the coral Madracis myriaster (Cnidaria: Pocilloporidae) was found as the main reef builder, offering habitat for many species of fish and invertebrates. In order to improve the study of deep-sea coral habitats, their connectivity and prospective management, nine new genetic markers (microsatellites) were developed for M. myriaster and tested in samples from PNNCP. We present the assessment of these markers, with a specificity for the deep coral, and its prospective use in future analysis for the PNNCP and other areas in the Caribbean and the Atlantic, where M. myriaster is reported. We also include an additional taxonomic analysis performed on samples of M. myriaster using scanning electron microscopy.

3D-Representations for studying deep-sea coral habitats in the Lacaze-Duthiers Canyon, from geological settings to individual specimens

The Lacaze-Duthiers Canyon is located in the western Mediterranean Sea and is long known for hosting cold-water coral colonies in the canyon head region at depths ranging from 250 to 550 m. In 2019 during the CALADU cruise, three kinds of 3D-reconstructions were applied to better understand the distribution of coral colonies, their habitat and their skeleton morphologies.The canyon's flanks were mapped using a hull-mounted echosounder and an ROV multibeam echosounder. Digital terrain models were built with resolutions of 5 and 1 m and examined in three dimensions. ROV bathymetric data collected on the canyon's flanks made it possible to highlight a series of sub-parallel structures identified as lithified sedimentary strata along which coral colonies grow.Coral assemblages were explored at four locations and photographic images were assembled using structure from motion techniques to build photogrammetric models. Coral assemblages reconstructed in 3D enabled geo-localizing and recreating coral colonies on 16 models over a total area of 4370 m2. Two colonial species, Madrepora oculata and Desmophyllum pertusum were plotted and reported on bathymetric models to interpret their location at the scale of the canyon. The coordinates and depth of the colonies were used to calculate the vertical distribution (limited to our small bathymetric exploration, between 339 and 214 m depth) and density of populations (up to 4.3 colonies per m2). The spatial coverage of the 16 assemblages measured between 100 and 600 m2 each. The sizes of the colonies were measured to analyze the population structures of both species (mean sizes of 28 cm for D. pertusum and 18 cm for M. oculata, maximum sizes 1 m and 0.5 m, respectively, bushes 2.5 m long). In addition, lost fishing gears were quantified, longlines measured and their densities calculated (0.16 m/m2, up to 0.30 m/m2). An area with exuberant orange colonies of D. pertusum was discovered for the first time in the Lacaze-Duthiers Canyon.Five deep-sea scleractinian species were collected and micro-tomographic scans computed to view their intrinsic skeleton organization. Micro-CT scans of M. oculata, D. pertusum, Desmophyllum dianthus, Caryophyllia smithii, and Dendrophyllia cornigera enabled longitudinal and transversal cuts, highlighting morphological criteria for species identification and the multidirectional examination of specimens. We observed a thin canal connecting calices along the axis of D. pertusum colonies, and separate calices along the axis of M. oculata colonies.

Bioaccumulation of Essential and Potentially Toxic Elements in the Muscle and Liver of the Spotted Ratfish (Hydrolagus colliei) From Deep-Sea Waters off the Northern Gulf of California.

This study aimed to establish the distribution of As, Cd, Cu, Pb, and Zn, in the muscle and liver of the spotted ratfish Hydrolagus colliei from the northern Gulf of California to establish the bioaccumulation background data in this species. The individuals (n = 110) were obtained by bycatch from the Gulf of California hake fisheries, and the metals and metalloid were measured by atomic absorption spectrometry. The element with the highest concentration in the muscle (15.19 ± 5.40mgkg-1) and the liver (20.98 ± 10.30mgkg-1) was As, followed by essential elements (Zn > Cu), and the lowest were the non-essential Pb (0.029 ± 0.014 and 0.048 ± 0.038mgkg-1, muscle and liver, respectively) and Cd (0.022 ± 0.014 and 0.796 ± 0.495mgkg-1, muscle and liver, respectively). The liver showed higher bioaccumulation than the muscle in all the studied elements. The sex was not a factor that influenced the bioaccumulation. The concentrations of As in the muscle did not exceed the maximum permissible limits of Mexican legislation, and < 50% of the samples exceed Cd and Pb limits of the Mexican, European Union, and WHO/FAO regulations. The differences found between the elements and tissues could be related to the different diets of the species, their migratory patterns, and their life conditions. Studies in the deep-sea water H. colliei are limited, and further investigations are needed regarding the feeding habits of H. colliei as well as the interactions of potentially toxic elements within the deep-sea water habitat.