Deep-sea Cores Research Articles

Gorgonophilus canadensis (Copepoda: Lamippidae) a parasite in the octocoral Paragorgia arborea – relation to host, reproduction, and morphology

The family Lamippidae (Cyclopoida) are endosymbionts mainly occurring in shallow water octocorals and records from deep-sea corals are few. Here we investigated the relationship between the lamippid Gorgonophilus canadensis Buhl-Mortensen & Mortensen, 2004 and its host the deep-sea coral Paragorgia arborea. Twenty-one specimens of G. canadensis was found inside eight gall-like structures on a P. arborea colony collected in 2010 at 318 m depth off Norway. The galls contained on average 1.6 females, 1.0 males, and 7.5 egg sacs estimated to contain 400 eggs each. Females were larger than males (4.6 mm compared to 2.0 mm). The gall volume increased with the number of egg sacs, females, and the length of females inside, the latter correlation was significant (p < 0.05). The number of egg sacs in galls was positively correlated with the abundance and length of females (p < 0.05), and by adding Canadian data from 17 galls the relation between egg sacs and numbers of females and males in galls became stronger (p < 0.01 and p < 0.05, respectively). Scanning electron microscopy revealed that this highly modified endoparasite has thoracic appendages with non-segmented flexible spines with a specialized structure at their tips through which threads are excreted. We speculate that this adaptation could relate to feeding or attachment of egg sacs inside the galls. Thread production has rarely been reported for copepods and we explore its function in the group as well as other crustaceans. The age and size of the parasite, and the introduction to and release from the host is also discussed.

A deep Tasman outflow of Pacific waters during the last glacial period

The interoceanic exchange of water masses is modulated by flow through key oceanic choke points in the Drake Passage, the Indonesian Seas, south of Africa, and south of Tasmania. Here, we use the neodymium isotope signature (εNd) of cold-water coral skeletons from intermediate depths (1460‒1689 m) to trace circulation changes south of Tasmania during the last glacial period. The key feature of our dataset is a long-term trend towards radiogenic εNd values of ~−4.6 during the Last Glacial Maximum and Heinrich Stadial 1, which are clearly distinct from contemporaneous Southern Ocean εNd of ~−7. When combined with previously published radiocarbon data from the same corals, our results indicate that a unique radiogenic and young water mass was present during this time. This scenario can be explained by a more vigorous Pacific overturning circulation that supported a deeper outflow of Pacific waters, including North Pacific Intermediate Water, through the Tasman Sea.

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.

State of Play in Marine Soundscape Assessments

A soundscape is the recording of all sounds present in an area, creating a holistic view of the acoustic profile in an ecosystem. Studying acoustic parameters of marine soundscapes as a whole has been shown to give an indication of the health status of the location, as well as correlate to which species may be present and using the area. With the rapid innovation of technology, especially data storage and declining cost of equipment, marine soundscape research is fast increasing, and these previous limitations have been switched for computing capacity for data analysis. Here, we perform a systematic assessment of literature of marine soundscape studies, from 1978, when the first soundscape study was reported, until 2021. We identified 200 primary research studies that recorded soundscapes and captured their geographical location, depth, habitat, duration of the study, and number of sites in each study. Using this data, we summarize the state of play in marine soundscapes studies, and identify knowledge gaps in the spatial coverage, depth profiles, habitat representation and study duration. Spatially, studies are biased towards the northern hemisphere. They are also more prevalent in more easily accessible ecosystems, in order from most to least studied, in coastal (38%), pelagic (20%), tropical coral reef (17%), rocky reef (7%), polar (5.5%), seagrass meadows, oyster reef and kelp/algal forest (&amp;lt;5% each) areas, with zones of cold-water coral the least studied (0.3%). Continuing the trend of accessibility, studies also tended to focus on shallow ecosystems. Most recordings (68%) were conducted in the upper 50 m, with 13% in 50-200 m depths, and only 0.6% at a depth &amp;gt;4000 m. With anthropogenic noise and other pollution sources increasing globally, these gaps in research should be further addressed, especially as they pertain to vulnerable ecosystems, many of which are affected by global climate change and anthropogenic influences. It is crucial that marine soundscape studies continue to be developed and pursued, to establish baselines for healthy ecosystems and/or document recovery following management actions.

A new octocoral species of Swiftia (Holaxonia, Plexauridae) from the upper bathyal off Mauritania (NE Atlantic).

Three species of the genus Swiftia are known for the NE Atlantic Ocean and Mediterranean Sea. Remotely-operated vehicle (ROV) surveys and sampling on board RV Maria S. Merian during cruise MSM 16/3 'PHAETON' in 2010 provided footage and specimens of octocorals off Mauritania. Micro-computed tomography (micro-CT) reveals, for the first time in taxonomy of octocorals, the three-dimensional arrangement of the sclerites in a polyp. Swiftiaphaeton sp. nov. is described for the continental slope off Mauritania. This azooxanthellate octocoral is distinctive from NE Atlantic and Mediterranean congenerics by the dark red colour of the colonies (including the polyps), the presence of a layer of rod sclerites on top of the polyp mounds, and different sizes of polyps and sclerites. Using micro-CT has allowed the observation and imaging of a layer of sclerites that is distinct from other species of the same genus. ROV images revealed live records of S.phaeton sp. nov. in submarine canyons and on cold-water coral mounds in the upper-bathyal off Mauritania (396-639 m depth), mainly attached to dead coral, coral rubble, or rocks. The new species represents an extension of the genus distribution to the tropical latitudes (17°07'N and 20°14'N) of the NE Atlantic Ocean.

Uncommon Polyketides from Penicillium steckii AS-324, a Marine Endozoic Fungus Isolated from Deep-Sea Coral in the Magellan Seamount

Four unusual steckwaic acids E–H (1–4), possessing a rarely described acrylic acid unit at C-4 (1–3) or a double bond between C-12 and C-13 (4) are reported for the first time, along with four new analogues (5–8) and two known congeners (9 and 10). They were purified from the organic extract of Penicillium steckii AS-324, an endozoic fungus obtained from a deep-sea coral Acanthogorgiidae sp., which was collected from the Magellan Seamount at a depth of 1458 m. Their structures were determined by the interpretation of NMR and mass spectroscopic data. The relative and absolute configurations were determined by NOESY correlations, X-ray crystallographic analysis, and ECD calculations. All compounds were tested for their antimicrobial activities against human- and aquatic-pathogenic bacteria and plant-related pathogenic fungi.

A health survey of the reef forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata in a remote submarine canyon on the European continental margin, NE Atlantic

Monitoring of cold-water corals (CWCs) for pathogens and diseases is limited due to the environment, protected nature of the corals and their habitat and as well as the challenging and sampling effort required. It is recognised that environmental factors such as temperature and pH can expedite the ability of pathogens to cause diseases in cold-water corals therefore the characterisation of pathogen diversity, prevalence and associated pathologies is essential. The present study combined histology and polymerase chain reaction (PCR) diagnostic techniques to screen for two significant pathogen groups (bacteria of the genus Vibrio and the protozoan Haplosporidia) in the dominant NE Atlantic deep-water framework corals Lophelia pertusa (13 colonies) and Madrepora oculata (2 colonies) at three sampling locations (canyon head, south branch and the flank) in the Porcupine Bank Canyon (PBC), NE Atlantic. One M. oculata colony and four L. pertusa colonies were collected from both the canyon flank and the south branch whilst five L. pertusa colonies were collected from the canyon head. No pathogens were detected in the M. oculata samples. Neither histology nor PCR detected Vibrio spp. in L. pertusa, although Illumina technology used in this study to profile the CWCs microbiome, detected V. shilonii (0.03%) in a single L. pertusa individual, from the canyon head, that had also been screened in this study. A macroborer was observed at a prevalence of 0.07% at the canyon head only. Rickettsiales-like organisms (RLOs) were visualised with an overall prevalence of 40% and with a low intensity of 1 to 4 (RLO) colonies per individual polyp by histology. L. pertusa from the PBC canyon head had an RLO prevalence of 13.3% with the highest detection of 26.7% recorded in the south branch corals. Similarly, unidentified cells observed in L. pertusa from the south branch (20%) were more common than those observed in L. pertusa from the canyon head (6.7%). No RLOs or unidentified cells were observed in corals from the flank. Mean particulate organic matter concentration is highest in the south branch (2,612 μg l−1) followed by the canyon head (1,065 μg l−1) and lowest at the canyon flank (494 μg l−1). Although the route of pathogen entry and the impact of RLO infection on L. pertusa is unclear, particulate availability and the feeding strategies employed by the scleractinian corals may be influencing their exposure to pathogens. The absence of a pathogen in M. oculata may be attributed to the smaller number of colonies screened or the narrower diet in M. oculata compared to the unrestricted diet exhibited in L. pertusa, if ingestion is a route of entry for pathogen groups. The findings of this study also shed some light on how environmental conditions experienced by deep sea organisms and their life strategies may be limiting pathogen diversity and prevalence.

The mineralization and early diagenesis of deep-sea coral Madrepora oculata

The skeletons of aragonitic corals carry essential information about oceanic environmental changes in the past. However, coral-based geochemical proxies are sensitive to vital effect and post-depositional diagenetic processes, which have not been well understood for deep-sea corals. In this study, we have investigated the mineralization and early diagenetic process of the dendroid stem of a dead deep-sea scleractinian coral sample (Madrepora oculata) collected by Remote Operated Vehicle (ROV) from a seamount in the Caroline Ridge, western Pacific. Despite being only ~270 years old, as dated by the U-series disequilibrium method, this sample already has extensive diagenesis including a visible chalky layer. The outermost chalky layer and the adjacent pristine skeleton of the sample were characterized by multiple mineralogical (SEM, XRD, EBSD, Raman Spectroscopy) and geochemical (ICP-OES, LA-ICP-MS, IR-MS, MC-ICP-MS) techniques. Skeletal stable C and O isotopes display strong linearity, with a trend pointing toward the theoretical isotopic composition of inorganically-precipitated aragonite from local seawater. This observation suggests that the epithecal mineralization of M. oculata is far from equilibrium with seawater and can be quantitatively explained by bio-mineralization models developed for solitary scleractinian corals. We further show that chalking of the outer layer, a common feature in sub-fossilized deep-sea corals, is caused by microbial-driven boring and μm-scale dissolution voids at an average rate of 3.5 μmol/cm2/y (scaled to the skeleton surface) without notable secondary infillings or mineralogical alternations. The higher average δ13C and δ18O of the chalky part than the pristine part might be due to the preferential dissolution of carbonate relatively depleted in 13C and 18O during alteration, and/or reduced isotope fractionation from seawater during coral mineralization of the outer layer. The chalky layer shows significantly higher Mn/Ca and Th/Ca ratios than the pristine part, characterized by Th/Mn ratios similar to that of the dissolved component of local seawater. Our study suggests that the incorporation of external Th into the coral skeleton is most likely associated with organic binding rather than detrital contamination, secondary carbonate mineral formation, adsorption onto surfaces of chalky aragonite or ferromanganese oxides, with important implications for coral U-series geochronology.

Environmental changes in SW France during the Middle to Upper Paleolithic transition from the pollen analysis of an eastern North Atlantic deep-sea core

AbstractEvaluating synchronies between climate and cultural changes is a prerequisite for addressing the possible effect of environmental changes on human populations. Searching for synchronies during the Middle-Upper Paleolithic transition (ca. 48–36 ka) is hampered by the limits of radiocarbon dating techniques and the large chronological uncertainties affecting the archaeological and paleoclimatic records, as well by their low temporal resolution. Here, we present a high-resolution, pollen-based vegetation record from the Bay of Biscay, sea surface temperature changes, additional14C ages, and a new IRSL date on the fine-sediment fraction of Heinrich Stadial (HS) 6. The IRSL measurements give an age of ca. 54.0 ± 3.4 ka. The paleoclimatic results reveal a succession of rapid climatic changes during the Middle-Upper Paleolithic transition in SW France (i.e. D-O 12–8 and two distinct climatic phases during HS 4). Comparison of the new paleoclimatic record with chronologically well-constrained regional archaeological changes shows that no synchronies exist between cultural transitions and environmental changes. The disappearance of Neanderthals and the arrival ofHomo sapiensin SW France encompassed a long-term forest opening, suggesting thatHomo sapiensmay have progressively replaced Neanderthals from D-O 10 to HS 4 through competition for the same ecological niches.

Geochronological Evidence Inferring Carbonate Compensation Depth Shoaling in the Philippine Sea after the Mid-Brunhes Event

Carbonate compensation depth (CCD) is an important factor in the global deep ocean and in global carbon cycling; however, its variabilities have not been well documented in previous studies. In this study, we investigate two deep-sea cores collected from the Philippine Sea in terms of geochronology and geochemical properties over the past ~900 kyr. The principle results are as follows: (1) Two magnetozones are determined from the sediment’s magnetic records, which can be correlated with the Brunhes and Matuyama chrons in the geomagnetic polarity timescale. (2) The age models can be refined by tuning the Ba and Sm intensities of the two studied cores to the global ice volume, and the estimated sediment accumulation rate is ~4 mm/kyr. (3) Chalky mud and the bulk carbon δ13C record vary abruptly at ~430 ka and imply 200 m shoaling of the CCD. Based on these results, a close link is inferred between marine productivity, aeolian dust, and CCD changes, which can be correlated with a major change that occurred during the Mid-Brunhes Event. Therefore, we propose that the sedimentary processes in the Philippine Sea are evidence of global climate change, providing a unique window to observe interactions between various environmental systems.

Non-Vent Megafaunal Communities on the Endeavour and Middle Valley Segments of the Juan de Fuca Ridge, Northeast Pacific Ocean

There has been increasing interest in mining polymetallic sulfide deposits at deep-sea inactive hydrothermal vents, leading to the development of regulations to minimize risk to the marine environment. While an extensive body of literature exists on the ecological communities at active vents, fauna at inactive hydrothermal vents and the vent periphery are poorly described and their vulnerability to disturbance is unknown. We examined patterns in abundance of non-vent epibenthic megafauna on two segments of the Juan de Fuca Ridge, Northeast Pacific Ocean. Video footage was collected by the remotely operated vehicle ROPOS during four dives at the Endeavour Segment and two dives at Middle Valley in August 2016. At the Endeavour Segment, the substrate is characterized predominantly by basalt and edifices of hydrothermal sulfide that range in hydrothermal activity from inactive to vigorous, high-temperature venting. In contrast, Middle Valley is heavily sedimented and most hydrothermal activity is low-temperature diffuse flow. While inactive substrates at both sites harboured slow-growing sessile fauna, the dominant members of the community differed between sites. At Endeavour, the most abundant morphotaxa included rossellid vase sponges, alcyonacean corals, and crinoids. Estimated richness and total abundance of morphotaxa was higher on hard substrates than sedimented substrates and highest on inactive chimneys. At Middle Valley, the most abundant morphotaxa included antipatharian corals, anemones, and ascidians. Species richness was higher on inactive chimneys and mixed substrates than sediment. The abundance of some megafauna varied with proximity to active vents. At Endeavour, deep-water corals were nearly absent within 25 m of active chimneys and very few occurred between 26 and 50 m from active chimneys. Rossellid vase sponges were in low abundance within 25 m of active chimneys but were more abundant than corals at 26-50 m from active chimneys. This project contributes baseline data on megafaunal assemblages on inactive hydrothermal vents and can provide the basis for more focused research on the structure and function of inactive vent ecosystems.

Accumulation of marine litter in cold-water coral habitats: A comparative study of two Irish Special Areas of Conservation, NE Atlantic

Cold-water corals (CWCs) have come under threat from anthropogenic activities such as fishing despite their ecological significance as biodiversity hotspots and as such are being protected in Europe under the EU Habitats Directive with some designated as Special Areas of Conservation (SACs). This study maps the distribution and sources of marine litter in CWC habitats in two SACs on the Irish margin. Data were collected with remotely operated vehicle in the SACs. The density, abundance and composition of litter were assessed, with differences observed between the two sites. The regional morphology influences the distribution of litter in the SACs, with CWC reefs and rock exposures trapping more marine litter. Fishing gear (80.7%) and plastics (55.1%) were commonly found. The observed fisheries-derived litter in the SACs exceed global averages of 10–20% fishing gear, suggesting the SACs appear to offer limited protection to the coral habitats with respect to marine litter.

Major environmental drivers determining life and death of cold-water corals through time.

Cold-water corals (CWCs) are the engineers of complex ecosystems forming unique biodiversity hotspots in the deep sea. They are expected to suffer dramatically from future environmental changes in the oceans such as ocean warming, food depletion, deoxygenation, and acidification. However, over the last decades of intense deep-sea research, no extinction event of a CWC ecosystem is documented, leaving quite some uncertainty on their sensitivity to these environmental parameters. Paleoceanographic reconstructions offer the opportunity to align the on- and offsets of CWC proliferation to environmental parameters. Here, we present the synthesis of 6 case studies from the North Atlantic Ocean and the Mediterranean Sea, revealing that food supply controlled by export production and turbulent hydrodynamics at the seabed exerted the strongest impact on coral vitality during the past 20,000 years, whereas locally low oxygen concentrations in the bottom water can act as an additional relevant stressor. The fate of CWCs in a changing ocean will largely depend on how these oceanographic processes will be modulated. Future ocean deoxygenation may be compensated regionally where the food delivery and food quality are optimal.

Multiscale mechanical consequences of ocean acidification for cold-water corals

Ocean acidification is a threat to deep-sea corals and could lead to dramatic and rapid loss of the reef framework habitat they build. Weakening of structurally critical parts of the coral reef framework can lead to physical habitat collapse on an ecosystem scale, reducing the potential for biodiversity support. The mechanism underpinning crumbling and collapse of corals can be described via a combination of laboratory-scale experiments and mathematical and computational models. We synthesise data from electron back-scatter diffraction, micro-computed tomography, and micromechanical experiments, supplemented by molecular dynamics and continuum micromechanics simulations to predict failure of coral structures under increasing porosity and dissolution. Results reveal remarkable mechanical properties of the building material of cold-water coral skeletons of 462 MPa compressive strength and 45–67 GPa stiffness. This is 10 times stronger than concrete, twice as strong as ultrahigh performance fibre reinforced concrete, or nacre. Contrary to what would be expected, CWCs retain the strength of their skeletal building material despite a loss of its stiffness even when synthesised under future oceanic conditions. As this is on the material length-scale, it is independent of increasing porosity from exposure to corrosive water or bioerosion. Our models then illustrate how small increases in porosity lead to significantly increased risk of crumbling coral habitat. This new understanding, combined with projections of how seawater chemistry will change over the coming decades, will help support future conservation and management efforts of these vulnerable marine ecosystems by identifying which ecosystems are at risk and when they will be at risk, allowing assessment of the impact upon associated biodiversity.

A review of Atlantic deep-water species in the genus Talassia (Caenogastropoda, Vanikoridae)

A review was done on all species of the genus Talassia (family Vanikoridae Gray, 1840), which are known from an upper bathyal depth range in the Atlantic Ocean. Four new species are proposed: Talassia mexicana sp. nov. from the Gulf of Mexico, T. laevapex sp. nov. and T. flexisculpta sp. nov. from off Mauritania and T. rugosa sp. nov. from off Angola. Empty shells of the new species were found in sediment samples collected in habitats associated with deep-water corals. The new species were compared with the type species Talassia coriacea (Manzoni, 1868) and the deep-water species T. tenuisculpta (R.B. Watson, 1873), T. dagueneti (de Folin, 1873) and T. sandersoni (A.E. Verrill, 1884). Particularly the shape and sculpture of the protoconch show regional differences. Other specific characteristics are macro- and micro-sculpture of the teleoconch.

Natural variability in seawater temperature compromises the metabolic performance of a reef-forming cold-water coral with implications for vulnerability to ongoing global change

Natural variability in seawater temperature compromises the metabolic performance of a reef-forming cold-water coral with implications for vulnerability to ongoing global change

Food from the Depths of the Mediterranean: The Role of Habitats, Changes in the Sea-Bottom Temperature and Fishing Pressure

As part of the “Innovations in the Food System: Exploring the Future of Food” Special Issue, this paper briefly reviews studies that highlight a link between deep-sea fishery resources (deep-sea food resources) and vulnerable marine ecosystems (VME), species, and habitats in the Mediterranean Sea, providing new insights into changes in commercial and experimental catches of the deep-sea fishery resources in the central Mediterranean over the last 30 years. About 40% of the total landing of Mediterranean deep-water species is caught in the central basin. Significant changes in the abundance of some of these resources with time, sea-bottom temperature (SBT), and fishing effort (FE) have been detected, as well as an effect of the Santa Maria di Leuca cold-water coral province on the abundance of the deep-sea commercial crustaceans and fishes. The implications of these findings and the presence of several geomorphological features, sensitive habitats, and VMEs in the central Mediterranean are discussed with respect to the objectives of biodiversity conservation combined with those of management of fishery resources.

The complete mitochondrial genome of Dendrophyllia minuscula (Cnidaria: Scleractinia) from the NEOM region of the Northern Red Sea

The scleractinian coral family Dendrophylliidae is a major component of shallow and deep-water coral ecosystems worldwide, but our knowledge on the evolutionary history of the family remains scarce. Here, we used ezRAD coupled with Illumina sequencing technology and reconstructed the complete mitochondrial genome of Dendrophyllia minuscula (GenBank accession number OL634845), from mesophotic depths in the Red Sea NEOM area. The mitochondrial genome of D. minuscula consisted of 19,054 bp, organized in 13 protein-coding genes, 2 rRNA genes, and 2 tRNA genes, in agreement with the Scleractinia typical mitogenome organization. This complete mitochondrial genome contributes toward a better knowledge of mesophotic and deep-water coral diversity and evolutionary history.

DNA Barcoding of Cold-Water Coral-Associated Ophiuroid Fauna from the North Atlantic

In this study we focus on the ophiuroid species associated with cold-water corals south of Iceland. The specimens were sampled with the ROV Phoca (GEOMAR) in three different areas, during the recent expedition MSM75 connected to the IceAGE_RR (Icelandic marine Animals: Genetics and Ecology_Reykjanes Ridge hydrothermal vent activity) project. In each area, several corals were sampled and the ophiuroid specimens identified to the species level. The integrative taxonomic approach, based on morphological characters and DNA barcoding with COI of the collected ophiuroids, revealed five species that live on corals: Ophiomitrella clavigera (Ljungman, 1865); Ophiomyxa serpentaria (Lyman, 1883); Ophiacantha cuspidata (Lyman, 1879); Ophiactis abyssicola (M. Sars, 1861); and Ophiolebes bacata Koehler, 1921. Some of the sampled deep-sea corals exclusively host the species O.clavigera. The collected species are therefore associated with different corals but do not demonstrate a species-specific distribution. The video data support the integrative taxonomy and confirm the ecological evidence.

A biogeographical assessment of deep-sea coral assemblages from coastwide visual surveys off California

During the period 1992–2014, we quantified 79,233 deep-sea corals (DSC; azooxanthellate corals occurring in cold or deep waters, generally >50 m) at depths 23–867 m from 1281 visual transects in areas of rocky substrata off northern, central, and southern California. DSC were present on 68% of transects at all depths and substrata types. Thirty-nine taxa and morphotypes from at least 19 families and 24 genera, including 20 species, were identified. Survey depths differed among study regions, overlapping between north and south at >575 m, and between central and south at <325 m. Within study regions, we examined taxa-specific depth and temperature ranges and quantified the spatial distribution of DSC densities. Across study regions, we interpreted species distributions in the context of the literature and biogeographic provinces off California, examined size distributions, and characterized assemblages relative to latitude and depth. We discovered depth range extensions for seven species, and provide the first taxa-specific in situ temperature data for the U.S. West Coast. Overall densities (number of colonies/100 m2) of DSC within study regions were 105.8 (north), 5.0 (central), and 7.3 (south), and highest densities occurred on mixed and hard substrata. We did not observe a change in density with depth. Density ‘hot’ spots (p < 0.05) were identified at multiple locations in the central and south regions for DSC (other than sea pens) and for sea pens, respectively. Despite survey depth differences, three species with large depth ranges were observed in all three study regions, and most species were observed in the biogeographical province(s) reported for them in the literature. Most DSC were ≤20 cm high and ≤10 cm wide; colonies >50 cm high and >40 cm wide were rare and found primarily in the south. Six DSC assemblages (p < 0.05) were identified. Mid-depth assemblages in the central and south differed considerably, while deep assemblages in the north and south were similar. A shallow assemblage comprised taxa shared by central and south regions. As the relative habitat value of DSC to fishes becomes more apparent, our results will provide invaluable information for the identification of essential fish habitat and priority areas in need of protection.