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Modern cold-water corals (CWCs) occur in a wide range of water depths, with Desmophyllum pertusum being one of the most common species. Pleistocene, Holocene, and modern coral mound formation by living CWC reefs have previously been described in the Porcupine Seabight from water depths greater than 700 m in the vicinity of the transitional zone between the Eastern North Atlantic Water and Mediterranean Outflow Water. Here we document occurrence of fossil corals retrieved from two cores at 370 m depth in the Macnas Mounds, a relatively shallow occurrence for mounds on the Irish shelf-edge. Both cores feature D. pertusum restricted to the upper two metres, immediately overlying an erosive surface and a coeval major down-core change in grain size from sand to mud. Radiocarbon dating of coral specimens indicates the CWC mounds initiated 7.82 Cal ky BP. Our study unequivocally documents the existence of Holocene shelf-edge coral mounds in the eastern Porcupine Seabight and highlights the possibility of other occurrences of CWCs in similar settings elsewhere in the northeast Atlantic. Given that no living CWCs were encountered in the study area, we suggest that the area previously experienced more favourable conditions for CWC mound initiation and development along the shelf-edge margin, possibly due to differing conditions in the European Slope Current which flows northward along the continental slope from south of the Porcupine Bank to the Faroe-Shetland Channel. [ABSTRACT FROM AUTHOR]

Climate change is reorganizing the planet's biodiversity, necessitating proactive management of species and habitats based on spatiotemporal predictions of distributions across climate scenarios. In marine settings, climatic changes will predominantly manifest via warming, ocean acidification, deoxygenation, and changes in hydrodynamics. Lophelia pertusa, the main reef-forming coral present throughout the deep Atlantic Ocean (>200 m), is particularly sensitive to such stressors with stark reductions in suitable habitat predicted to accrue by 2100 in a business-as-usual scenario. However, with new occurrence data for this species along with higher-resolution bathymetry and climate data, it may be possible to locate further climatic refugia. Here, we synthesize new and published biogeographic, geomorphological, and climatic data to build ensemble, multi-scale habitat suitability models for L. pertusa on the continental margin of the southeast United States (SEUS). We then project these models in two timepoints (2050, 2100) and four climate change scenarios to characterize the occurrence probability of this critical cold-water coral (CWC) habitat now and in the future. Our models reveal the extent of reef habitat in the SEUS and corroborate it as the largest currently known essentially continuous CWC reef province on earth, and also predict abundance of L. pertusa to identify key areas, including those outside areas currently protected from bottom-contact fishing. Drastic reductions in L. pertusa climatic suitability index emerged primarily after 2050 and were concentrated at the shallower end (

The health status of cold-water coral reefs on the West African coast was investigated with the main objective of obtaining knowledge of the adaptive capacity of Lophelia pertusa to environmental stressors. Three coral sites were studied, in Northern Morocco, in the Morocco/Mauritania region (both in 2020) and, in the Ghana and Ivory coast region (visited in 2012, 2017, and 2019). Area cover of live colonies, explored through underwater videos, was used as an indicator of reef health and compared with the environmental variables: reef position, depth, water mass, temperature, dissolved oxygen concentration (DO), carbonate chemistry (pH, aragonite saturation (ΩAr), macronutrients and particles (visual). For a broader picture of the adaptations presented by Lophelia our results were compared with reefs in contrasting environments. Off Ghana and Mauritania healthy reefs (i.e., having areas with more than 20 % cover of live colonies) were found to reside at DO concentrations between 1.1 and 1.6 ml L−1, in corrosive waters (pH 7.7 and ΩAr 1.0) with high nutrient concentrations. By contrast, the reefs off the North of Morocco, sitting in well-oxygenated waters with oversaturated ΩAr, had no or few live colonies. Our findings together with data from other studies show that Lophelia has a wide tolerance to hypoxia and acidification, and that in relation to climate change increased temperature and silting could pose more serious threats. These findings highlight the importance of continued studies of Lophelia reefs in contrasting environmental conditions to better understand their adaptation potential to climate change-related stressors. [ABSTRACT FROM AUTHOR]

Cold‐water corals (CWCs) are important species that provide habitat for other taxa but are sensitive to mechanical damage from bottom trawling. CWC conservation has been implemented in the form of marine protected areas (MPAs), but recovery from impact may be particularly slow in the deep‐sea environment; consequently, the use of restoration techniques has been considered. To gain some insight into CWC recruitment and growth, in 2011 we deployed small seabed moorings in the Darwin Mounds MPA (~1,000 m water depth). This site hosts hundreds of CWC mounds, that had previously (until 2003) been impacted by deep‐water trawling. In 2019, we carried out in situ visual surveys of these moorings and the surrounding seabed environment, then recovered two of the moorings. The mooring buoys, glass floats with plastic covers, were extensively colonized by a diverse epifauna that included the CWCs Desmophyllum pertusum and D. dianthus. The presence of coral recruits indicated that environmental conditions, and larval supply, remained favorable for the settlement and growth of CWCs within the MPA. Based on our observations, we consider four possible restoration methods, together with a "do‐nothing" option, for the Darwin Mounds CWCs that have shown little, if any, natural recovery despite 16 years of protection. We conclude that seabed emplacement of high‐relief artificial substrata is likely to be the most efficient and cost‐efficient means of promoting enhanced recovery of the CWCs. [ABSTRACT FROM AUTHOR]

Over the past decade, an abundance of 16S rRNA gene surveys have provided microbiologists with data regarding the prokaryotes present in a coral-associated microbial community. Functional gene studies that provide information regarding what those microbes might do are fewer, particularly for non-tropical corals. Using the GeoChip 5.0S microarray, we present a functional gene study of microbiomes from five species of cold-water corals collected from depths of 296–1567 m. These species included two octocorals, Acanthogorgia aspera and Acanthogorgia spissa, and three stony corals: Desmophyllum dianthus, Desmophyllum pertusum (formerly Lophelia pertusa), and Enallopsammia profunda. A total of 24,281 gene sequences (representing different microbial taxa) encoding for 383 functional gene families and representing 9 metabolic gene categories were identified. Gene categories included metabolism of carbon, nitrogen, phosphorus, and sulfur, as well as virulence, organic remediation, metal homeostasis, secondary metabolism and phylogeny. We found that microbiomes from Acanthogorgia spp. were the most functionally distinct but also least diverse compared against those from stony corals. Desmophyllum spp. microbiomes were more similar to each other than to E. profunda. Of 383 total gene families detected in this study, less than 20% were significantly different among these deep-water coral species. Similarly, out of 59 metabolic sub-categories for which we were able to make a direct comparison to microbiomes of tropical corals, only 7 were notably different: anaerobic ammonium oxidation (anammox), chitin degradation, and dimethylsulfoniopropionate (DMSP) degradation, all of which had higher representations in deep-water corals; and chromium homeostasis/resistance, copper homeostasis/resistance, antibiotic resistance, and methanogenesis, all of which had higher representation in tropical corals. This implies a broad-scale convergence of the microbial functional genes present within the coral holobiont, independent of coral species, depth, symbiont status, and morphology. [ABSTRACT FROM AUTHOR]

ABSTRACT Recent deep-ocean exploration has uncovered a variety of cold-water coral (CWC) ecosystems around the world ocean, but it remains unclear how microbiome is associated with these corals at a molecular levels. This study utilized metabarcoding, tissue section observation, and metatranscriptomes to investigate the microbiome (Symbiodiniaceae and bacteria) of CWC species (Narella versluysi, Heterogorgia uatumani, and Muriceides sp.) from depths ranging from 260 m to 370 m. Warm-water coral (WWC) species (Acropora pruinosa, Pocillopora damicornis, and Galaxea fascicularis) were used as control groups. Results revealed that CWC host diverse bacteria and Symbiodiniaceae cells were observed in endoderm of CWC tissues. Several new candidate bacterial phyla were found in both CWC and WWC, including Coralsanbacteria, Coralqiangbacteria, Coralgsqaceae, Coralgongineae, etc. Both the 16S rRNA gene sequencing and metatranscriptomes revealed that Actinobacteria and Proteobacteria were abundant bacterial phyla in CWC. At the gene transcription level, the CWC-associated Symbiodiniaceae community showed a low-level transcription of genes involved in photosynthesis, CO2 fixation, glycolysis, citric acid cycle, while bacteria associated with CWC exhibited a high-level transcription of genes for carbon fixation via the Wood-Lijungdahl pathway, short chain fatty acids production, nitrogen, and sulfur cycles. IMPORTANCE This study shed new light on the functions of both Symbiodiniaceae and bacteria in cold-water coral (CWC). The results demonstrated that Symbiodiniaceae can survive and actively transcribe genes in CWC, suggesting a possible symbiotic or parasitic relationship with the host. This study also revealed complete non-photosynthetic CO2 fixation pathway of bacteria in CWC, as well as their roles in short chain fatty acids production and assimilation of host-derived organic nitrogen and sulfur. These findings highlight the important role of bacteria in the carbon, nitrogen sulfur cycles in CWC, which were possibly crucial for CWC survival in in deep-water environments.

Cold-water corals form an important part of temperate benthic ecosystems by increasing three-dimensionality and providing an important ecological substrate for other benthic fauna. However, the fragile three-dimensional structure and life-history characteristics of cold-water corals can leave populations vulnerable to anthropogenic disturbance. Meanwhile, the ability of temperate octocorals, particularly shallow-water species, to respond to adjustments in their environment linked to climate change has not been studied. This study reports the first genome assembly of the pink sea fan (Eunicella verrucosa), a temperate shallow-water octocoral species. We produced an assembly of 467 Mb, comprising 4,277 contigs and an N50 of 250,417 bp. In total, 213 Mb (45.96% of the genome) comprised repetitive sequences. Annotation of the genome using RNA-seq data derived from polyp tissue and gorgonin skeleton resulted in 36,099 protein-coding genes after 90% similarity clustering, capturing 92.2% of the complete Benchmarking Universal Single-Copy Orthologs (BUSCO) ortholog benchmark genes. Functional annotation of the proteome using orthology inference identified 25,419 annotated genes. This genome adds to the very few genomic resources currently available in the octocoral community and represents a key step in allowing scientists to investigate the genomic and transcriptomic responses of octocorals to climate change. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) has provoked changes in the carbonate saturation state that may alter the formation and structural biomineralisation of calcium carbonate exoskeletons for marine organisms. Biomineral production in organisms such as cold-water corals (CWC) rely on available carbonate in the water column and the ability of the organism to sequester ions from seawater or nutrients for the formation and growth of a skeletal structure. As an important habitat structuring species, it is essential to examine the impact that anthropogenic stressors (i.e., OA and rising seawater temperatures) have on living corals and the structural properties of dead coral skeletons; these are important contributors to the entire reef structure and the stability of CWC mounds. In this study, dead coral skeletons in seawater were exposed to various levels of pCO2 and different temperatures over a 12-month period. Nanoindentation was subsequently conducted to assess the structural properties of coral samples’ elasticity (E) and hardness (H), whereas the amount of dissolution was assessed through scanning electron microscopy. Overall, CWC samples exposed to elevated pCO2 and temperature show changes in properties which leave them more susceptible to breakage and may in turn negatively impact the formation and stability of CWC mound development.

Sulfitobacter is one of the major sulfite-oxidizing alphaproteobacterial groups and is often associated with marine algae and corals. Their association with the eukaryotic host cell may have important ecological contexts due to their complex lifestyle and metabolism. However, the role of Sulfitobacter in cold-water corals remains largely unexplored. In this study, we explored the metabolism and mobile genetic elements (MGEs) in two closely related Sulfitobacter faviae strains isolated from cold-water black corals at a depth of ~1000 m by comparative genomic analysis. The two strains shared high sequence similarity in chromosomes, including two megaplasmids and two prophages, while both contained several distinct MGEs, including prophages and megaplasmids. Additionally, several toxin-antitoxin systems and other types of antiphage elements were also identified in both strains, potentially helping Sulfitobacter faviae overcome the threat of diverse lytic phages. Furthermore, the two strains shared similar secondary metabolite biosynthetic gene clusters and genes involved in dimethylsulfoniopropionate (DMSP) degradation pathways. Our results provide insight into the adaptive strategy of Sulfitobacter strains to thrive in ecological niches such as cold-water corals at the genomic level. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) has provoked changes in the carbonate saturation state that may alter the formation and structural biomineralisation of calcium carbonate exoskeletons for marine organisms. Biomineral production in organisms such as cold-water corals (CWC) rely on available carbonate in the water column and the ability of the organism to sequester ions from seawater or nutrients for the formation and growth of a skeletal structure. As an important habitat structuring species, it is essential to examine the impact that anthropogenic stressors (i.e., OA and rising seawater temperatures) have on living corals and the structural properties of dead coral skeletons; these are important contributors to the entire reef structure and the stability of CWC mounds. In this study, dead coral skeletons in seawater were exposed to various levels of pCO2 and different temperatures over a 12-month period. Nanoindentation was subsequently conducted to assess the structural properties of coral samples' elasticity (E) and hardness (H), whereas the amount of dissolution was assessed through scanning electron microscopy. Overall, CWC samples exposed to elevated pCO2 and temperature show changes in properties which leave them more susceptible to breakage and may in turn negatively impact the formation and stability of CWC mound development. [ABSTRACT FROM AUTHOR]

Vertical walls of submarine canyons represent features of high conservation value that can provide natural areas of protection for vulnerable marine ecosystems under increasing anthropogenic pressure from deep-sea trawling. Wall assemblages are spatially heterogeneous, attributed to the high environmental heterogeneity over short spatial scales that is a typical feature of canyons. Effective management and conservation of these assemblages requires a deeper understanding of the processes that affect faunal distribution patterns. Canyons are recognised as sites of intensified hydrodynamic regimes, with focused internal tides enhancing near-bed currents, turbulent mixing and nepheloid layer production, which influence faunal distribution patterns. Faunal patterns also respond to broad-scale hydrodynamics and gradients in water mass properties (e.g. temperature, salinity, dissolved oxygen concentration). Oscillating internal tidal currents can advect such gradients, both vertically and horizontally along a canyon's walls. Here we take an interdisciplinary approach using biological, hydrodynamic and bathymetry-derived datasets to undertake a high-resolution analysis of a subset of wall assemblages within Whittard Canyon, North-East Atlantic. We investigate if, and to what extent, patterns in diversity and epibenthic assemblages on deep-sea canyon walls can be explained by spatial and temporal variability induced by internal tides. Vertical displacement of water mass properties by the internal tide was calculated from autonomous ocean glider and shipboard CTD observations. Spatial patterns in faunal assemblage structure were determined by cluster analysis and non-metric Multi-Dimensional Scaling plots. Canonical Redundancy Analysis and Generalised Linear Models were then used to explore relationships between faunal diversity and assemblage structure and a variety of environmental variables. Our results support the hypothesis that internal tides influence spatial heterogeneity in wall faunal diversity and assemblages by generating both spatial and temporal gradients in hydrodynamic properties and consequently likely food supply.

Framework-forming scleractinian cold-water corals (CWCs) act as ecosystem engineers, building and supporting biodiversity hotspots in the deep sea worldwide. While spatial patterns and drivers of species distributions have been evaluated on modern CWC reefs, little is known about how reef diversity is affected by habitat variability over geologic time – the scale at which CWC reefs initiate, thrive, and decline. Using three CWC reef sediment cores as species diversity archives, we investigated temporal trends of molluscan diversity over the last ~13 kyr from a CWC mound in the Alboran Sea (western Mediterranean Sea) to evaluate (a) how spatial patterns of CWC-associated diversity are recorded in reef sediments, (b) the potential of CWC reefs as biodiversity hotspots when coral growth is flourishing and when it is not, and (c) which palaeoceanographic conditions or habitat characteristics may be driving biodiversity. Our results reveal that at the ecosystem scale ecological differences between CWC habitats are more pronounced than ecological signatures of molluscan assemblages associated with intervals of CWC framework (flourishing growth) or non-framework (negligible CWC growth). However, within habitats, significant differences emerge between these assemblages with lower molluscan diversity associated with flourishing CWC growth. Significant negative correlations between molluscan diversity and palaeoceanographic conditions conducive for CWC growth (high food availability, strong hydrodynamics, optimal bottom-water temperatures and salinities, and high aggradation rates indicative of flourishing CWC growth also imply that CWC growth and relevant environmental conditions contribute to reduced molluscan diversity. Additionally, high coral volume, used here as a proxy for habitat structural complexity, is positively correlated with molluscan diversity just as high habitat complexity is in living CWC reefs. Altogether, these patterns detected over geologic time resemble those observed spatially across living CWC reefs today – where competition with resources, particularly food, prevents high reef biodiversity in the immediate vicinity of dense living CWC colonies. Overall, our study demonstrates that (1) ecological paradigms of living CWCs are preserved in their sedimentary record, (2) flourishing CWC growth and conditions promoting CWC growth drive habitat-scale diversity patterns, and (3) a geological approach can be applied to study long-term diversity dynamics in CWC ecosystems.

Biological rhythms are widely known in terrestrial and marine systems, where the behaviour or function of organisms may be tuned to environmental variation over periods from minutes to seasons or longer. Although well characterized in coastal environments, phenology remains poorly understood in the deep sea. Here we characterized intra-annual dynamics of feeding activity for the deep-sea octocoral Paragorgia arborea. Hourly changes in polyp activity were quantified using a time-lapse camera deployed for a year on Sur Ridge (1230 m depth; Northeast Pacific). The relationship between feeding and environmental variables, including surface primary production, temperature, acoustic backscatter, current speed and direction, was evaluated. Feeding activity was highly seasonal, with a dormancy period identified between January and early April, reflecting seasonal changes in food availability as suggested by primary production and acoustic backscatter data. Moreover, feeding varied with tides, which likely affected food delivery through cyclic oscillation in current speed and direction. This study provides the first evidence of behavioural rhythms in a coral species at depth greater than 1 km. Information on the feeding biology of this cosmopolitan deep-sea octocoral will contribute to a better understanding of how future environmental change may affect deep-sea coral communities and the ecosystem services they provide. [ABSTRACT FROM AUTHOR]

The Western Antarctic Peninsula is home to a diverse assemblage of deep-sea species and is warming faster than any other region in the Southern Hemisphere. This study investigated how larval development of the Antarctic cold-water coral Flabellum impensum was affected by temperatures consistent with ocean warming trends predicted for the twenty-first century. F. impensum larvae were cultured under four temperature conditions and scanning electron microscopy, transmission electron microscopy, and flow cytometry were used to compare settlement, mortality, larval size, development, deformity, and cellular health over the course of 44 days. While temperature did not impact settlement, mortality, or larval stress, the warmer treatments did have a significant impact on developmental rate. Samples exposed to warmer conditions developed faster than those in cooler conditions. Increased developmental rates were not accompanied by increased stress indicators such as deformity, mortality, or programmed cell death, suggesting that larval health was not negatively impacted by the rate change and may indicate that F. impensum larvae are tolerant of warming temperatures. Development and deformity assessments considered larval condition during the period between release and settlement, when larvae are thought to be especially sensitive to environmental impacts, and when the effects of those impacts on settlement or mortality may be particularly consequential for biogeography and population survival. These results suggest that larval development of F. impensum may be largely resistant to ocean warming trends predicted for the twenty-first century. [ABSTRACT FROM AUTHOR]

Sulfitobacter is one of the major sulfite-oxidizing alphaproteobacterial groups and is often associated with marine algae and corals. Their association with the eukaryotic host cell may have important ecological contexts due to their complex lifestyle and metabolism. However, the role of Sulfitobacter in cold-water corals remains largely unexplored. In this study, we explored the metabolism and mobile genetic elements (MGEs) in two closely related Sulfitobacter faviae strains isolated from cold-water black corals at a depth of ~1000 m by comparative genomic analysis. The two strains shared high sequence similarity in chromosomes, including two megaplasmids and two prophages, while both contained several distinct MGEs, including prophages and megaplasmids. Additionally, several toxin-antitoxin systems and other types of antiphage elements were also identified in both strains, potentially helping Sulfitobacter faviae overcome the threat of diverse lytic phages. Furthermore, the two strains shared similar secondary metabolite biosynthetic gene clusters and genes involved in dimethylsulfoniopropionate (DMSP) degradation pathways. Our results provide insight into the adaptive strategy of Sulfitobacter strains to thrive in ecological niches such as cold-water corals at the genomic level.

The occurrence of cold-water coral (CWC) reefs off Northwest Africa that has a broad oxygen minimum zone (OMZ) is poorly studied. A 400 km long almost continuous coral mound chain off Mauritania that was investigated by earlier expeditions revealed mainly dead corals. In 2021, the EAF-Nansen Programme conducted a survey at the border between Mauritania and Senegal with the main objective to map CWCs. Acoustic mapping with multibeam echosounder was used to target mounds at 450–650 m depth and 14 video lines were conducted using a remotely operated vehicle (ROV). The occurrence and health status of CWC reefs along video transects were annotated using the software "CampodLogger", oceanographic variables were measured using a CTD sonde, and terrain and backscatter analysis were conducted. Here we present the environment and health status of 13 Lophelia reefs established in the study area, six of them were large and healthy reefs with areas having 15–50% cover of live colonies. Oxygen concentrations were measured to be as low as 1 ml L−1 and temperature ranged from 8.8 to 11.6° C. We compare reef health with the environmental variables: temp, salinity, oxygen, and particle load. A GIS based model was developed to predict the occurrence of live reefs in the study area based on the observed average range of a set of terrain descriptors measured where live Lophelia reefs occurred. Our findings of healthy Lophelia reefs are unexpected and further north in the OMZ reefs have been described as dormant. There is an urgent need for visual seafloor mapping to aid the development of spatial management plans in these understudied waters. • Low oxygen concentration in the OMZ is not hindering the growth of Lophelia reefs. • Coral reef observations and modelled distribution indicates the presence of many reefs on the west Africa coast. • Our mapping of reefs has provided urgently needed information for coastal management. [ABSTRACT FROM AUTHOR]

Culture experiments are uniquely suited for uncovering the fundamental factors controlling skeletal geochemistry because it is possible to explore conditions beyond what is found in the modern ocean and to decouple parameters that co-vary in nature. We cultured juvenile individuals of a cold-water coral (Balanophyllia elegans) in a set of experiments that decoupled carbonate chemistry parameters over a wide range of pH, DIC, and [CO 3 2−] values. Using a multi-element mixed spike isotope dilution method we then analyzed cultured skeletons for U/Ca, which has been proposed as a potential proxy for seawater pH and [CO 3 2−], as well as Sr/Ca, and Mg/Ca. We find that U/Ca and Sr/Ca ratios in cultured B. elegans are most strongly correlated with solution DIC and not pH or [CO 3 2−]. We also confirm previous observations that Metal/Calcium (Me/Ca) ratios follow the same correlated relationships between and among individuals across different experimental conditions. Interpretation of these robust Me/Ca patterns within the framework of a geochemical model of biomineralization allows us to identify two "rules" of skeletal growth for B. elegans. First, changes in seawater exchange rates can explain variability in B. elegans Me/Ca ratios, correlations between these ratios, and sensitivity of Me/Ca to changes in seawater carbonate chemistry. Second, our model best fits our data if we assume that calcifying fluid pH for B. elegans remains constant across widely varying experimental seawater compositions. Our study has implications for the recently developed Sr-U paleothermometer because it refines our understanding of the environmental parameters affecting this proxy. Our model further demonstrates that U/Ca is not a robust indicator of seawater pH or [CO 3 2−]. Instead, U/Ca may record how calcifying fluid [CO 3 2−] responds to changes in the environment or calcification dynamics, which may be useful in evaluating how corals respond to changes like ocean acidification. Measurements of U/Ca and additional Me/Ca ratios in other coral species, evaluated within a similar framework, may elucidate how those species respond to environmental change. [ABSTRACT FROM AUTHOR]

Cold‐water coral reefs constitute important biodiversity hotspots in aphotic waters around the world. The complex, highly variable morphology of the reef habitat‐forming species has important implications for the communities they harbor and for the physical processes occurring therein. Lophelia pertusa (Desmophyllum pertusum) is one of the most common reef‐building cold‐water corals, but its morphological diversity has never been characterized on a broad scale. We qualitatively and quantitatively explored the patterns of morphological variation of this species over a wide geographic and ecological range, addressing corallite and colony traits and their interrelation. Geographic variation is evident at both corallite and colony level, although with distinct trends. By linking branching patterns to colony morphology, we identified three main morphotypes (asymmetrical, bushy, and columnar) with substantial geometric and architectural differences, which suggest high functional diversity of cold‐water coral reefs across regions. Colony morphology appears strongly governed by asexual budding of individual polyps, but largely decoupled from corallite morphology. We hypothesize that colony morphology is primarily driven by local hydrodynamic conditions and associated food supply. [ABSTRACT FROM AUTHOR]

Abstract Cold‐water coral reefs constitute important biodiversity hotspots in aphotic waters around the world. The complex, highly variable morphology of the reef habitat‐forming species has important implications for the communities they harbor and for the physical processes occurring therein. Lophelia pertusa (Desmophyllum pertusum) is one of the most common reef‐building cold‐water corals, but its morphological diversity has never been characterized on a broad scale. We qualitatively and quantitatively explored the patterns of morphological variation of this species over a wide geographic and ecological range, addressing corallite and colony traits and their interrelation. Geographic variation is evident at both corallite and colony level, although with distinct trends. By linking branching patterns to colony morphology, we identified three main morphotypes (asymmetrical, bushy, and columnar) with substantial geometric and architectural differences, which suggest high functional diversity of cold‐water coral reefs across regions. Colony morphology appears strongly governed by asexual budding of individual polyps, but largely decoupled from corallite morphology. We hypothesize that colony morphology is primarily driven by local hydrodynamic conditions and associated food supply.

Cold-water coral (CWC) communities are biodiversity hotspots on the world's deep seafloor. Although deep-sea corals in the South China Sea (SCS) have been reported before, they are only sporadic. A comprehensive and systematic understanding of the CWC in the SCS would forge the basis for future protection. Here we conducted the first systematic survey on the CWCs in the following six broad-scale sub-regions, from the northwest and northeast slopes to the seamounts in the western and central basins of the SCS, through twenty-four dives of the human-occupied vehicle ShenhaiYongshi. Statistical analysis provided detailed information on the distribution, abundance, size, diversity, and density of CWCs and the in situ environmental conditions supporting coral habitats. We found that the SCS hosted highly diversified coral communities, including twelve genera of gorgonians, six genera of black corals, and one genus of stony corals. The differences in the spatial distribution patterns of coral communities suggested that several environmental variables (depth, temperature, salinity, substrate, and geomorphology) might influence the development of CWCs in the SCS. The intermediate water layer of the SCS appeared to provide suitable habitat for deep-sea coral communities and potentially promoted connectivity. Furthermore, differences between sub-regions within the SCS may be an important factor responsible for the biogeographic patterns of CWCs. These sub-regions of CWCs were observed to range from 0.004 to 0.622 corals m−2, with an average of 0.139 corals m−2. The mean density of CWCs in the SCS was relatively high compared to well-studied CWC hotspots. Overall, the results revealed the significance of the SCS as an important CWC hotspot in the world. These findings provide a fundamental basis for the protection of deep-sea coral assemblages in the SCS. • Through 24 HOV dives, numerous in-situ observations of deep-sea corals over a large range of the SCS. • This study provides a detailed first-hand documentation of cold-water corals in the SCS, which are rarely known so far. • The SCS is one of the world's most important cold-water coral hotspots. [ABSTRACT FROM AUTHOR]

Benthic fauna form spatial patterns which are the result of both biotic and abiotic processes, which can be quantified with a range of landscape ecology descriptors. Fine- to medium-scale spatial patterns (200 m2 were created and all organisms were geotagged in order to illustrate their point pattern. The pair correlation function was used to establish whether organisms demonstrated a clustered pattern (CP) at various scales. We further applied a point pattern modelling approach to identify four potential point patterns: complete spatial randomness (CSR), an inhomogeneous pattern influenced by environmental drivers, random clustered point pattern indicating biologically driven clustering and an inhomogeneous clustered point pattern driven by a combination of environmental drivers and biological effects. Reef framework presence and structural complexity determined inhabitant distribution with most organisms showing a departure from CSR. These CPs are likely caused by an affinity to local environmental drivers, growth patterns and restricted dispersion reproductive strategies within the habitat across a range of fine to medium scales. These data provide novel and detailed insights into fine-scale habitat heterogeneity, showing that non-random distributions are apparent and detectable at these fine scales in deep-sea habitats.

Cold-water corals (CWCs) are important habitats for creatures in the deep-sea environment, but they have been degraded by anthropogenic activity. So far, no genome for any CWC has been reported. Here, we report a draft genome of Trachythela sp. which represents the first genome of CWCs to date. In total, 56 and 65 Gb of raw reads were generated from Illumina and Nanopore sequencing platforms, respectively. The final assembled genome was 578.26 Mb, which consisted of 396 contigs with a contig N50 of 3.56 Mb, and the genome captured 90.1% of the metazoan Benchmarking Universal Single-Copy Orthologs. We identified 335 Mb (57.88% of the genome) of repetitive elements, which is a higher proportion compared with others in the Cnidarians, along with 35,305 protein-coding genes. We also detected 483 expanded and 51 contracted gene families, and many of them were associated with longevity, ion transposase, heme-binding nicotinamide adenine dinucleotide, and metabolic regulators of transcription. Overall, we believe this genome will serve as an important resource for studies on community protection for CWCs. [ABSTRACT FROM AUTHOR]

Submarine canyons support high biomass communities as they act as conduits where sediments, nutrients, and organic matter from continental shelves, or those that are carried along by slope currents, are transported into the abyssal zone. The Porcupine Bank Canyon (PBC), located on the Irish continental margin and isolated from terrigenous inputs, reveals a complex terrain and substrate variation that affect the distribution of benthic fauna. Here, ROV-based benthic video, conductivity-temperature-depth (CTD), current velocity profiles, suspended particulate organic matter (POM) and bathymetric data were assessed to determine the controls on the distribution of benthic megafauna throughout the canyon. Multivariate analysis of the benthic community reveals significant differences in community structure among habitats and site locations throughout the canyon. Furthermore, these results show that non-reef habitats exhibit more variation in the composition of benthic taxa than coral reef and rubble habitats, with the following species contributing most to the structural differentiation between habitats: Leiopathes glaberrima (12.46%), Hexadella dedritifera (10.37%), Cidaris cidaris (9.31%), Aphrocallistes beatrix (9.33%), Araeosoma fenestratum (9.11%), Stichopathes cf. abyssicola (7.39%), Anthomastus grandiflorus (4.66%), and Benthogone rosea (3.84%). In addition, greater diversity, taxa evenness and high abundance of motile fauna were observed in non-reef habitat and the canyon flank. Seabed terrain features (depth, slope) are the most important environmental drivers that affect benthic taxa distribution while site locations and habitat type are the categorical variables that influence taxa distribution in the PBC. The highest mean current speed was observed on the canyon flank where the highest Shannon’s diversity was recorded while mean current speed ranged from 18.2–31.3 cm s–1. As the PBC is cut off from direct terrigenous input, this research contributes to understanding cold-water coral habitat responses to natural Northeast Atlantic environmental conditions. The findings of the current study will inform key stakeholders on how to responsibly interact with the canyon benthic habitats and can help inform policy makers on the effective conservation and management of the cold-water coral habitat in the PBC and other canyons.

Knowledge of people's understanding of environmental problems is vital for the effective implementation of the ecosystem approach to marine management. This is especially relevant when conservation goals are aimed at ecosystems in the deep-sea that are remote to the consciousness of most people. This study explores public perceptions of the deep-sea environment among the Scottish and Norwegian public. It further analyses the relationships between respondents' pro-environmental concerns toward the marine environment and personal characteristics using a multiple indicators multiple causes model. The results show that public knowledge of the deep-sea environment is low for Scottish and moderate for Norwegians. Awareness of cold-water corals was high for the Lofoten case study area amongst the Norwegian public and low for the Mingulay reef complex in the Scottish case. These differences might arise because Norway is known to host the world's largest cold-water corals in the Lofoten area; a fact that has been well-publicized. We find that most people think changes in the deep-sea have at least some effect on them. On average, the public perceive the deep-sea condition to be at most “fairly good” but are dissatisfied with the management of it with approximately only one third or less thinking it is well-managed. Generally, the public perception from both countries show ecocentric attitudes toward the marine environment implying that they recognize the value of ecosystem services, the current ecological crisis and the need for sustainable management.

Aim: The Deepwater Horizon disaster resulted in the largest accidental marine oil spill in history and caused extensive injury to deep‐sea habitats, including cold‐water coral communities dominated by Paramuricea species. One of the primary difficulties in assessing the full extent of the injury to cold‐water coral ecosystems is the extreme paucity of observational data and the subsequent lack of knowledge of their distribution within the affected region. The aim of this study was to use habitat suitability modelling to estimate the number of potentially affected Paramuricea sp. corals across the northern Gulf of Mexico. Location: Northern Gulf of Mexico. Taxon: Cold‐water corals in the genus Paramuricea. Methods: High‐resolution (12.5 m) models were built using the maximum entropy (Maxent) approach using remotely sensed data including seafloor topography, seismic reflectivity, temperature and the amount of productivity exported from the surface. Model outputs were used to estimate the number of potential coral sites in the northern Gulf of Mexico, delineated as areas with both high habitat suitability scores and the presence of hard substrate. The number of coral sites was further adjusted using a ground‐truthing procedure using autonomous underwater vehicle‐transect data. Results: Across the entire study area in the northern Gulf of Mexico, there were 558 predicted coral sites, covering an area of 14.2 km2. Within a 2,291 km2 region shown to have been directly affected by the spill and subsequent oil plume, there were 66 predicted coral sites covering an area of 1.2 km2 with an average of 63 corals per site. Main Conclusions: Our results indicate that the magnitude of injury stemming from the spill was likely far higher than previously known, and will help quantify the full extent of the losses incurred as well as prioritize disturbed areas for future research and restoration efforts. [ABSTRACT FROM AUTHOR]

Cold-water coral (CWC) reefs are distributed globally and form complex three-dimensional structures on the deep seafloor, providing habitat for numerous species. Here, we measured the community O2 and dissolved inorganic nitrogen (DIN) flux of CWC reef habitats with different coral cover and bare sediment (acting as reference site) in the Logachev mound area (NE Atlantic). Two methodologies were applied: the non-invasive in situ aquatic eddy co-variance (AEC) technique, and ex situ whole box core (BC) incubations. The AEC system was deployed twice per coral mound (69 h in total), providing an integral estimate of the O2 flux from a total reef area of up to 500 m2, with mean O2 consumption rates ranging from 11.6 ± 3.9 to 45.3 ± 11.7 mmol O2 m–2 d–1 (mean ± SE). CWC reef community O2 fluxes obtained from the BC incubations ranged from 5.7 ± 0.3 to 28.4 ± 2.4 mmol O2 m–2 d–1 (mean ± SD) while the O2 flux measured by BC incubations on the bare sediment reference site reported 1.9 ± 1.3 mmol O2 m–2 d–1 (mean ± SD). Overall, O2 fluxes measured with AEC and BC showed reasonable agreement, except for one station with high habitat heterogeneity. Our results suggest O2 fluxes of CWC reef communities in the North East Atlantic are around five times higher than of sediments from comparable depths and living CWCs are driving the increased metabolism. DIN flux measurements by the BC incubations also revealed around two times higher DIN fluxes at the CWC reef (1.17 ± 0.87 mmol DIN m–2 d–1), compared to the bare sediment reference site (0.49 ± 0.32 mmol DIN m–2 d–1), due to intensified benthic release of NH4+. Our data indicate that the amount of living corals and dead coral framework largely contributes to the observed variability in O2 fluxes on CWC reefs. A conservative estimate, based on the measured O2 and DIN fluxes, indicates that CWC reefs process 20 to 35% of the total benthic respiration on the southeasterly Rockall Bank area, which demonstrates that CWC reefs are important to carbon and nitrogen mineralization at the habitat scale.

Keratoisis grayi is one of the most abundant large gorgonian corals found off Newfoundland and Labrador, yet we know little regarding the factors influencing its distribution, abundance, and condition. We employed remotely operated vehicle (ROV) transect data collected in three canyons off the Grand Banks, Newfoundland to quantitatively examine the influence of depth, bottom type, canyon, and trawling intensity on K. grayi abundance, height, and condition at small spatial scales. While surveying 105 km of seafloor with a ROV, we observed 5770 K. grayi colonies and 167 trawl marks. We found that K. grayi were significantly more likely to occur in boulder areas than in cobble or gravel. Bottom depth related positively and significantly with colony height and our models predict that the largest bamboo coral colonies occur in boulders in Halibut Channel, and in boulders and cobble in Haddock Channel. The majority of colonies observed were alive and undamaged, but tipped, broken, dead and partially dead colonies were also recorded. K. grayi were more likely to occur in trawled areas, but these colonies were more likely to be damaged, broken, smaller in size, and less abundant than colonies outside trawled areas. These results demonstrate a negative impact of bottom trawling on K. grayi colonies off Newfoundland and Labrador and that fishers may specifically target areas where these corals occur.

The “Little MonSta” benthic lander array consists of 8 ROV-deployable (remotely operated vehicle) instrumented lander platforms for monitoring physical and chemical oceanographic properties and particle sampling developed as part of the MMMonKey_Pro program (mapping, modeling, and monitoring key processes and controls in cold-water coral habitats in submarine canyons). The Little MonStas offer flexible solutions to meet the need to monitor marine benthic environments during a historically unprecedented time of climate-driven oceanic change, develop an understanding of meso-scale benthic processes (natural and man-made), and to calibrate geological environmental archives. Equipped with acoustic Doppler current profilers (ADCPs), sediment traps, nylon settlement plates and homing beacons, the compact and upgradable lander platforms can be deployed by ROVs to precise locations in extreme terrains to a water depth of 3000 m. The array allows cluster-monitoring in heterogeneous environments or simultaneous monitoring over wider areas. A proof-of-concept case study was presented from the cold-water coral habitable zone in the upper Porcupine Bank Canyon, where the Little MonStas collected 868.8 h of current speed, direction, temperature, and benthic particulate flux records, as well as 192 particle samples subsequently analyzed for particular organic carbon (POC), lithic sediment, live foraminifera, and microplastics. The potential to upgrade the Little MonStas with additional sensors and acoustic releases offers greater and more flexible operational capabilities.

Fine-scale structural complexity created by reef-building coral in shallow-water environments is influential on biodiversity, species assemblage and functional trait expression. Cold-water coral reefs are also hotspots of biodiversity, often attributed to the hard surface and structural complexity provided by the coral. However, that complexity has seldom been quantified on a centimetric scale in cold-water coral reefs, unlike their shallow-water counterparts, and has therefore never been linked in a similar way to the reef inhabitant community. Structure from motion techniques which create high-resolution 3D models of habitats from sequences of photographs is being increasingly utilised, in tandem with 3D spatial analysis to create useful 3D metrics, such as rugosity. Here, we demonstrate the use of ROV video transect data for 3D reconstructions of cold-water coral reefs at depths of nearly 1000 m in the Explorer Canyon, a tributary of Whittard Canyon, NE Atlantic. We constructed 40 3D models of approximately 25-m-length video transects using Agisoft Photoscan software, resulting in sub-centimetre resolution reconstructions. Digital elevation models were utilised to derive rugosity metrics, and orthomosaics were used for coral coverage assessment. We found rugosity values comparable to shallow-water tropical coral reef rugosity. Reef and nearby non-reef communities differed in assemblage composition, which was driven by depth and rugosity. Species richness, epifauna abundance and fish abundance increased with structural complexity, being attributed to an increase in niches, food, shelter and alteration of physical water movement. Biodiversity plateaued at higher rugosity, illustrating the establishment of a specific reef community supported by more than 30% coral cover. The proportion of dead coral to live coral had limited influence on the community structure; instead, within-reef patterns were explained by depth and rugosity, though our results were confounded to a certain extent by multi-collinearity. Fine-scale structural complexity appeared to be integral to local-scale ecological patterns in cold-water coral reef communities. [ABSTRACT FROM AUTHOR]

Data from two experimental longline surveys and two video inspections carried out in Santa Maria di Leuca cold‐water coral province (Mediterranean Sea) during spring–autumn 2010 were used in order to compare the benthopelagic abundance and diversity between coral and non‐coral habitats and between different devices. The sampling was carried out in two types of habitat: a coral habitat with carbonate mounds and a non‐coral habitat characterized by intermound sea floor.A Bayesian hierarchical modelling approach to accommodate factors influencing community assemblages was used considering the number of species, the Shannon–Wiener diversity index and the two most abundant species represented by the European conger (Conger conger) and blackbelly rosefish (Helicolenus dactylopterus).A relevant effect of the habitat factor was observed for both the number of species and the diversity index, showing a higher species number and diversity index in the coral habitat than in the non‐coral habitat. Concerning the relevance of fixed effects from the model on the probability of observing non‐zero (positive) abundances, the devices considered, longline and baited lander, did not show different influence for either C. conger or H. dactylopterus. In the case of positive abundance, a relevant device effect was only observed for H. dactylopterus, showing higher abundances for longline than for baited lander. A habitat effect was detected, with positive abundances for both species in the coral habitat.This study proves that structurally complex habitats generated by cold‐water corals influence the distribution and diversity of the benthopelagic fauna, and that the use of different devices can provide complementary useful results. Increased knowledge about the role of cold‐water corals in the associated benthopelagic fauna could lead to better conservation of one of the most important hot spots of biodiversity in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

• Radiometric ages of CWC of the Adriatic Sea shows different colonization periods. • The first occurrence of CWC in the southern Adriatic Sea is dated to the LGM. • The lack of CWC during the S1 documents oxygen deficiency at intermediate depths. • The NAdDW trajectory along the W Adriatic Sea controls the asymmetrical CWC settling. The deep southern Adriatic Sea is home of widespread cold-water coral colonization (Madrepora oculata , Lophelia pertusa , Desmophyllum dianthus) which is at present limited by large to its western (Apulian) margin and central part, including the Bari Canyon system. On the contrary, the eastern side is today almost deprived of significant coral growth and this asymmetrical distribution has been ascribed primarily to the action of the North Adriatic Dense Water (NAdDW) that impinges more efficiently on the Apulian margin. The collection of subfossil specimens of M. oculata , L. pertusa and D. dianthus provided the very first dates for cold-water coral colonization along the eastern margin. Once combined with known distribution of live cold-water corals and fossil occurrences in the southern Adriatic Sea, uranium-series dating provides evidence of (i) coral presence in the southeastern Adriatic during the Last Glacial Maximum (LGM), followed by (ii) a time of basin-wide colonization after the post-Last Glacial Maximum and encompassing the Younger Dryas, (iii) another time of undocumented coral presence with the onset of Sapropel S1. Perturbations of the thermohaline circulation in this sector of the Mediterranean basin might have governed the presence and demise of the resident cold-water coral populations interfering with strength and trajectories of main water masses. It is hypothesized that the achievement of the current asymmetrical distribution did occur since the end of S1 protracting to present time. The post-S1 reorganization likely brought to the current hydrological situation where the influence of NAdDW prevails in the western side and corals are doing at best on its trajectory. The scarcity of datable material makes the proposed scenario open to debate and in need of further supporting evidence. [ABSTRACT FROM AUTHOR]

Cold-water corals are highly sensitive to changes in water temperature, as it is an important determinant of their distribution. In recent years, several heatwave events have occurred in multiple marine ecosystems, including the northeast Pacific Ocean. However, the effects of elevated ocean temperatures on cold-water corals are largely unknown. Determining the upper thermal limits of cold-water octocorals is an important first step in identifying if warm-water events pose a potential threat. Temperature data were obtained from loggers placed in the Channel Islands National Marine Sanctuary (CINMS) at 20, 50, 100, and 200 m prior to the 2015–2016 El Niño Southern Oscillation (ENSO) event and used to characterize warm-water anomalies. Live colonies of the common gorgonian octocoral, Adelogorgia phyllosclera, were collected from the CINMS using a remotely operated vehicle (ROV) and transported to laboratory aquaria where they were maintained. A laboratory study was conducted to investigate the upper thermal limit of A. phyllosclera during a series of temperature assays using coenenchyme health scores, polyp activity, and estimated survival. Results of in-situ temperature analyses indicated that warm-water anomalies occurred frequently at 50 and 100 m, with most of these anomalies occurring during strong ENSO months. Based on the laboratory temperature assays, the upper thermal limit of A. phyllosclera was estimated to be 20 °C, with a time to effect of 96 hours. During the 2015–2016 ENSO event, this upper thermal limit was exceeded (21.1 °C) by warm-water anomalies at 20 m that lasted up to 14.1 hours, and approached (18.3 °C) by warm-water anomalies at 50 m that lasted up to 52.7 hours. Projections for future warm-water events suggest that the upper thermal limit of A. phyllosclera and other cold-water corals will likely be reached more frequently in the coming years. Thus, understanding the responses of cold-water corals to thermal stress will help predict the resilience of these species to future ocean warming. • Study assessed the potential implications of marine heatwaves on cold-water corals. • Used in situ temperature logger data to inform laboratory temperature assays. • Warm-water anomalies are occurring at depths where cold-water corals exist. • These anomalies did briefly reach the upper lethal limit of a species of cold-water coral. [ABSTRACT FROM AUTHOR]

Abstract Assessing the physicochemical variability of the deeper ocean is currently hampered by limited instrumental time series and proxy records. Bamboo corals (Isididae) form a cosmopolitan family of calcitic deep sea corals that could fill this information gap via geochemical information recorded in their skeletons. Here we evaluate the suitability of high-resolution chemical imaging of bamboo coral skeletons for temperature and nutrient reconstruction. The applied elemental mapping techniques allow to verify the suitability of the chosen transect on the sample section for paleo-reconstructions and enhance the statistical precision of the reconstruction. We measured Mg/Ca via electron microprobe at 1 μm resolution and Ba/Ca via laser ablation ICP-MS at 35 μm resolution in a historic specimen of Keratoisis grayi from the Blake Plateau off Eastern Florida. Long-term growth temperatures of 7.1 ± 3.4 °C (2SD) that are in agreement with recent ambient temperature range can be reconstructed from Mg/Ca ratios provided that anomalously Mg-enriched structural features around the central axis and isolated features related to tissue attachment are avoided for reconstruction. Skeletal Ba/Ca measurements reflect mean seawater barium [Ba] SW concentrations ([Ba] SW = 51 ± 24 nmol kg−1 (2SD)), in agreement with instrumental data (47 nmol kg−1). We show for the first time that Ba/Ca forms concentric structures in a bamboo coral skeleton section. Our investigations suggest that, while bamboo coral skeletons do record environmental parameters in their mean chemical composition, the magnitude of environmental variability reconstructed from high-resolution chemical maps exceeds that expected from instrumental time series. This necessitates additional investigation of the factors driving bamboo coral skeletal composition. [ABSTRACT FROM AUTHOR]

Cold‐water coral (CWC) ecosystems are protected both in national and international waters. They are considered Vulnerable Marine Ecosystems and, in addition, meet the criteria to be defined ecological or biological significant areas.Two new sites of the "Sardinian CWC province" were discovered by means of remotely operated vehicle surveys in two submarine canyons in the north‐eastern portion of the Sardinian continental margin, at depths ranging from 230 to 430 m.Dense and healthy patches of small and medium‐sized Madrepora oculata colonies were found dwelling on rocky walls and inclined silted soft bottoms.A rich and diverse associated megafauna was found within both live and dead portions of the coral framework. In addition, the presence of benthic litter and derelict fishing gears were also documented.These results further extend the "Sardinian CWC province" extension, providing insights of a potential CWC network along the Sardinian continental margin with implications for the Mediterranean mosaic of CWC provinces, further stressing the need for urgent conservation measures for these habitats. [ABSTRACT FROM AUTHOR]

Highlights • CWC settlement was studied in two Mediterranean canyons using three habitat suitability models. • Hydrodynamic models have been used in the habitat suitability models, for both canyons. • Seafloor roughness was the first variable explaining CWC distribution. • Hydrodynamic variables were also important to explain CWC settlement. • Bottom-current velocity has an impact on CWC settlement at local scale. Abstract Madrepora oculata and Lophelia pertusa are the two main ecosystem engineering, scleractinian cold-water corals (CWC) found in Mediterranean canyons. Factors controlling CWC distribution in the Mediterranean Sea are not yet fully understood in spite of such ecosystems being recognized as sensitive habitats by the General Fisheries Commission for the Mediterranean. As they are threatened by fishery activity, they are subject to management and protection measures. In order to contribute towards identifying the major drivers governing CWC distribution at local scale, which is a prerequisite for proper management, we focused our attention on two canyons: (1) the Cassidaigne canyon, located in the eastern part of the Gulf of Lion, in which CWC ecosystems have settled in an upwelling environment and form large colonies, and (2) the Bari Canyon System, in the southwestern Adriatic, a site of coral growth that has been hypothesized to respond to hydrographic processes, including the cascading of North Adriatic Dense Water. The objective of our study was to combine several ecological variables to describe the environmental conditions in favor of CWC settlement and growth: (1) CWC observations, extracted from geo-referenced underwater videos, (2) seafloor characteristics derived from high-resolution bathymetry, (3) data on local hydrodynamic conditions (from high resolution hydrodynamic models). Habitat suitability models were used to identify the main variables driving CWC distribution. Models based on presence-only data (Maxent and ENFA) and on presence-absence data (GLMs) were fitted and compared. Seafloor ruggedness was identified to be the major factor driving CWC distribution in both canyons with the three methods. Two hydrodynamic variables (mean temperature and current velocity) were the second most important predictors for explaining CWC settlement and growth. Suitable areas for CWC habitat occurrence were mapped for both canyons. Spatial distributions were generally predicted at the same locations, although the GLM gave less realistic results in the Bari canyon system probably due to the limited range cover of the entire environmental conditions by the absence points, suggesting that the Maxent and ENFA models were more efficient. These theoretical distributions will help in the assessment of potential habitat extent in the deep-sea and also in the scheme of the Marine Strategy Framework Directive (MSFD). [ABSTRACT FROM AUTHOR]

Tisler Reef is a Norwegian cold-water coral reef in the Northeastern Skagerrak, which lies at an average depth of 120 m, is constructed principally of the scleractinian coral Lophelia pertusa and hosts a dynamic and diverse ecosystem. The availability of oxygen within Tisler Reef, recorded between 2006 and 2008, showed a decline during the summer months, caused by both the isolation of the reef from the atmosphere under conditions of seasonal stratification, and the enhanced respiration in the water column during the seasonal zooplankton proliferations. Concentrations of dissolved oxygen were replenished from high-current flows advecting water from off the reef. Low current flow conditions (< 0.05 m s−1) coincided with a short-term reduction in oxygen, the extent of which varied seasonally and were observed to be greatest during July and August, coinciding with the summer Calanus proliferation in the Skagerrak. Normalized acoustic backscatter amplitude during the summer months showed a strong signal of zooplankton diurnal vertical migration, coinciding with the lowest oxygen concentrations at the reef observed during, and lagging slightly after, the deep phase of the zooplankton vertical migration. This effect was most obvious during low-flow conditions; highlighting the importance of zooplankton and associated activity as a consumer of oxygen at the reef. [ABSTRACT FROM AUTHOR]

A chain of paired mound and depression structures are presented in the southwestern continental shelf of the Ulleung Basin, East Sea, Korea. We integrate multibeam bathymetry to identify topographic features, sub-bottom profile and multi-channel seismic reflection data to confirm geological features, and piston cores to understand the sediments of the mounds and depressions. Paired structures occur with a northwest–southeast orientation at water depths between 130 and 150 m and have similar scales of 10–20 m in height and depth. The mounds consist of cold-water corals and authigenic carbonate with shelly sand, whereas, the surficial lithology of depressions are only composed of siliciclastic deposits. The mounds appeared to have grown from the depression based on the observation for morphological features in the cross-section profiles of the paired mound and depression structures. Seismic profiles show acoustic blanking anomalies and seismic chimneys, indicating that the topographic relief formed under the influence of gas seepage. The petrological and geochemical signature of carbonate chunks also displayed gas leak effects different from CWC. This study suggests a developmental history model with paired mound and depression structures, in which gas/fluid escape causes depressions and the selective coral growth creates mounds growing on one side of these depressions. The mounds had sufficiently grown, depressions would have been further developed in interaction with the bottom current. • The seafloor mounds consist of authigenic carbonate and cold-water coral that is L. pertusa. • Cold-water coral may have settled on authigenic carbonates that act as a hard bottom. • Cold-water coral colonized the mounds at least during the late Holocene. • The depressions initially are formed by gas and developed by the bottom current. [ABSTRACT FROM AUTHOR]