Cold-water Coral Communities Research Articles

Oasis of the deep: Cold-water corals of the South China Sea

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.

Deep-sea biology in undergraduate classrooms: Open access data from remotely operated vehicles provide impactful research experiences

Opportunities for students to conduct research in courses increase feelings of belonging in science, retention in STEM majors, and sense of ownership in a student’s educational experience. However, many research fields are challenging to bring to students: for example, deep-sea biology often requires expensive expeditions, restricting participation and accessibility. Access to deep-sea systems has been expanded by programs such as the National Oceanic and Atmospheric Administration's Ocean Exploration (NOAA Ocean Exploration), which uses telepresence to bring deep-sea exploration to a global audience. Here, we present one example of how remotely operated vehicles can engage students in original research. Students in an undergraduate Marine Biology lab at at the State University of New York at Geneseo investigated the relationship between substrate rugosity and biodiversity of cold-water coral communities and associate fauna. The study site in the Pacific Remote Islands Marine National Monument was explored by NOAA Ocean Exploration using NOAA Ship Okeanos Explorer as part of the 2017 Mountains in the Deep Expedition, EX1705. Organism density was greater at higher rugosity levels, suggesting that complex substrates support higher abundances in deep-sea communities. This research experience enhanced student’s understanding of the scientific process, appreciation for deep-sea communities, and engagement in the course. Open access deep-sea data provide impactful opportunities for students to participate in original research, increasing the accessibility and reach of deep-sea science.

Deep-water species assemblages on the trawlable bottoms of the Central Mediterranean: Changes or not over time?

Deep-sea communities are impacted by several anthropogenic activities, such as fisheries, which still remain one of the most damaging on the marine environments in terms of biodiversity loss and habitat degradation. The north-western Ionian Sea (Central Mediterranean) experienced long-standing trawl fishing activity with the exploitation of deep-sea demersal resources. The integrate analysis with data of both benthic, demersal and benthopelagic species collected during a time series of experimental trawl survey, yearly carried out in the Ionian basin down to 800 m in depth, allowed to asses the current status of the Ionian deep-sea faunal assemblages and their potential changes overtime. Multivariate analysis and univariate indices, modelled using Generalized Additive Model (GAM) framework, confirm a depth zonation pattern of deep-sea faunal assemblages in the study area, with the presence of two distinct epibathyal and mesobathyal groups. GAM also highlighted a temporal effect on the biodiversity indices, with significant negative trends of diversity and evenness indices as well as a significant increasing of dominance one, over the study period 2012-2020. The benthic community is characterised by more generalist species and a simplified structure, with a severe depletion in habitat-former taxa whereas the demersal and benthopelagic fauna of the Ionian Sea show a general stability in the overall structure if compared with previous studies lasting over two decades. The presence of complex and heterogenous habitats unsuitable for trawl, like cold-water coral communities and canyon systems, provide Essential Fish Habitats (EFHs) for commercial species, acting as potential renewal areas for exploited resources in the neighbouring fishing grounds. These findings encourage an ecosystem-based management including spatial considerations for the objectives of biodiversity conservation combined with those of management of fishery resources.

Spatial and temporal distribution of cold-water corals in the Northeast Atlantic Ocean over the last 150 thousand years

Scleractinian cold-water corals are found across the Northeast Atlantic, providing structure for important habitats that support high biodiversity. Climate-driven perturbations on parameters such as carbonate chemistry, oxygen, bottom currents, productivity and temperature have the potential to impact the abundance and diversity of these cold-water coral communities. One way to explore the linkage between corals and climate is to examine historic coral distributions during times of past climate change. Previous coral dating efforts in the Northeast Atlantic (n ∼ 700) have focused on reef-forming colonial coral communities from shelf and slope areas. However, there are far fewer data from open-ocean settings or from solitary coral species, thus precluding assessment of basin-wide controls on coral occurrence. Here, we contribute >600 new U-series ages for both solitary and colonial coral species from open-ocean sites including the Reykjanes Ridge and seamounts in the mid and low latitudes to map the changing distribution of Northeast Atlantic cold-water corals over the last 150,000 years. The temporal occurrences of solitary and colonial corals from our offshore sites are broadly similar to the distributions along the nearer-shore sites at the same latitudes. In the cold-temperate and high-latitude Northeast Atlantic, corals are most abundant during warm climate intervals, with the Reykjanes Ridge (60°N) representing the northernmost limit of corals in the Northeast Atlantic during Marine Isotope Stage (MIS) 5, MIS 3 and Bølling-Allerød. This biogeographical distribution expanded northwards to the Norwegian margin at the onset of the Holocene when the ice sheets retreated and modern-like oceanographic conditions were established. We interpret the abundance of corals at these northerly sites to be linked with increased food supply and favourable hydrological conditions. By contrast, coral sites south of 45°N are characterised by glacial and deglacial occurrences, with a marked decline during the Holocene. This distribution is also linked to food supply, potentially driven by shifts in dust fertilization and upwelling, in addition to changes in dissolved oxygen concentration and temperature. Together, these findings emphasize the links between climate, oceanic processes, and cold-water coral distribution, pointing to low food supply and low oxygen concentration as limiting factors for cold-water coral populations. Both parameters are changing in the modern ocean, with implications for future coral communities.

Diversity, structure and spatial distribution of megabenthic communities in Cap de Creus continental shelf and submarine canyon (NW Mediterranean)

The continental shelf and submarine canyon off Cap de Creus (NW Mediterranean) were declared a Site of Community Importance (SCI) within the Natura 2000 Network in 2014. Implementing an effective management plan to preserve its biological diversity and monitor its evolution through time requires a detailed characterization of its benthic ecosystem. Based on 60 underwater video transects performed between 2007 and 2013 (before the declaration of the SCI), we thoroughly describe the composition and structure of the main megabenthic communities dwelling from the shelf down to 400 m depth inside the submarine canyon. We then mapped the spatial distribution of the benthic communities using the Random Forest algorithm, which incorporated geomorphological and oceanographic layers as predictors, as well as the intensity of the bottom-trawling fishing fleet. Although the study area has historically been exposed to commercial fishing practices, it still holds a rich benthic ecosystem with over 165 different invertebrate (morpho)species of the megafauna identified in the video footage, which form up to 9 distinct megabenthic communities. The continental shelf is home to coral gardens of the sea fan Eunicella cavolini, sea pen and soft coral assemblages, dense beds of the crinoid Leptometra phalangium, diverse sponge grounds and massive aggregations of the brittle star Ophiothrix fragilis. The submarine canyon off Cap de Creus is characterized by a cold-water coral community dominated by the scleractinian coral Madrepora oculata, found in association with several invertebrate species including oysters, brachiopods and a variety of sponge species, as well as by a community dominated by cerianthids and sea urchins, mostly in sedimentary areas. The benthic communities identified in the area were then compared with habitats/biocenoses described in reference habitat classification systems that consider circalittoral and bathyal environments of the Mediterranean. The complex environmental setting characteristic of the marine area off Cap de Creus likely produces the optimal conditions for communities dominated by suspension- and filter-feeding species to develop. The uniqueness of this ecosystem and the anthropogenic pressures that it faces should prompt the development of effective management actions to ensure the long-term conservation of the benthic fauna representative of this marine area.

Involving fishers in scaling up the restoration of cold-water coral gardens on the Mediterranean continental shelf

Cold-water gorgonians dwelling on the continental shelf are a common by-catch of bottom-contact fishing practices. Given the slow growth and limited recruitment of cold-water gorgonians, the impact of fishing activities may seriously compromise the conservation of the highly complex coral gardens communities. For this reason, the development of effective active and passive restoration methods is nowadays a priority in order to enhance the natural recovery of impacted cold-water coral gardens. However, the ecological restoration of mesophotic and deep-sea communities remains extremely limited, due to its technological requirements and associated costs, which bring its wide-scale and long-term application into question. This study reports the preliminary results of the first large-scale active restoration of more than 400 cold-water gorgonians on the Mediterranean continental shelf. By actively involving local fishers during two consecutive fishing seasons, by-catch gorgonians were recovered and returned to the continental shelf (at 80–90 m depth). The monitoring surveys performed by using an Autonomous Underwater Vehicle (AUV) revealed that 460 gorgonian transplants survived over an area of 0.23 ha. The reintroduced cold-water gorgonian population was compared to a reference natural population in terms of size and spatial structure. The cost of the restoration amounted to 140,000 €/ha, which is significantly lower than that of any deep-sea restoration actions performed to date. The results of this cost-effective active restoration highlight the viability of large-scale restoration of impacted cold-water coral communities, with promising results for the conservation and recovery of mesophotic and deep-sea ecosystems.

Characterization of deep-sea benthic invertebrate megafauna of the Galapagos Islands

The deep sea represents the largest and least explored biome on the planet. Despite the iconic status of the Galapagos Islands and being considered one of the most pristine locations on earth, the deep-sea benthic ecosystems of the archipelago are virtually unexplored in comparison to their shallow-water counterparts. In 2015, we embarked on a multi-disciplinary scientific expedition to conduct the first systematic characterization of deep-sea benthic invertebrate communities of the Galapagos, across a range of habitats. We explored seven sites to depths of over 3,300 m using a two-part Remotely Operated Vehicle (ROV) system aboard the E/V Nautilus, and collected 90 biological specimens that were preserved and sent to experts around the world for analysis. Of those, 30 taxa were determined to be undescribed and new to science, including members of five new genera (2 sponges and 3 cnidarians). We also systematically analysed image frame grabs from over 85 h of ROV footage to investigate patterns of species diversity and document the presence of a range of underwater communities between depths of 290 and 3,373 m, including cold-water coral communities, extensive glass sponge and octocoral gardens, and soft-sediment faunal communities. This characterization of Galapagos deep-sea benthic invertebrate megafauna across a range of ecosystems represents a first step to study future changes that may result from anthropogenic impacts to the planet’s climate and oceans, and informed the creation of fully protected deep-water areas in the Galapagos Marine Reserve that may help preserve these unique communities in our changing planet.

Cold-Water Coral Mound Archive Provides Unique Insights Into Intermediate Water Mass Dynamics in the Alboran Sea During the Last Deglaciation

The Alboran Sea is widely recognized to host numerous cold-water coral ecosystems, including the East Melilla Coral Province. Yet, their development through time and response to climatic variability has still to be fully understood. Based on a combined investigation of benthic foraminiferal assemblages, foraminiferal stable isotope compositions, grain size analysis, sediment geochemistry, and macrofaunal quantification, this study identifies key events and processes having governed cold-water coral development at the East Melilla Coral Province between Greenland Stadial 2.1 and the Early Holocene. The transition from Greenland Stadial 2.1 to Greenland Interstadial 1 is associated to a decline of bryozoan communities and their replacement by cold-water corals, together with changes in benthic foraminiferal assemblages and a decrease in the sediment mean grain size. These results suggest that a rapid decrease in bottom currents and the establishment of dysoxic and mesotrophic conditions at the seafloor, possibly associated to enhanced fluvial input, resulted in the decline of bryozoans as the dominant suspension feeding organisms and their replacement by a thriving cold-water coral community. This transition from a bryozoan to a coral dominated environment is concomitant with the beginning of the African Humid Period, confirming that increasing fluvial input could have been a main factor triggering the establishment of cold-water corals in the East Melilla Coral Province during Greenland Interstadial 1. A change in benthic foraminiferal communities and an increase in the sediment mean grain size mark the passage from the Early to Late Greenland Interstadial 1. The current velocity of intermediate water masses is suggested to have increased during the Early to Late Greenland Interstadial 1, whilst simultaneously fluvial input would have reduced. Such changes suggest that the climate became more arid during the second phase of Greenland Interstadial 1.

Control of Deep Currents on Sediment and Cold-Water Coral Distribution on the Northern Manihiki Plateau

High-definition video surveys of remotely operated vehicle (ROV) dives from the NOAA’s Mountains in the Deep 2017 expedition (EX1705) cruise along volcanic ridges and seamounts of the Manihiki Plateau coupled with multibeam bathymetry data and water column profiles, reveal no or minimal sediment cover on the basaltic edifice, but variable amounts of cold-water corals on ferromanganese-encrusted basaltic rocks. Coarse sediment, however, accumulates in crevasses and sedimentary ripples testify the existence of currents in the area. Collectively, these observations illustrate the strong influence of deep currents on the surficial geology and cold-water coral distribution at ~2,000 m water depths. Dive transects along two basaltic seamounts show stark differences of sedimentary features and cold-water coral distribution. On the ridges of “Te Kawhiti” (water depth: 2,089-2,220 m), basaltic slabs, and cold-water corals are far more abundant in comparison to the slope of a mesa in “Te Tuku” (water depth: 2,440-2,495 m). The increased abundance on “Te Kawhiti” is due to the exposure of “Te Kawhiti” to Lower Circumpolar Deep Water that sweeps the summit of the ridges as indicated by frequent ripples observed in between the basaltic rocks. The currents are strong enough to sweep fine-grained sediments away, leaving coarse-grained sediments behind, inducing the formation of ferromanganese crust on the basaltic rocks. Both dive sites are below the high-Mg calcite saturation horizon, and as a result, the cold-water coral community is dominated by Isididae, which can build a high-Mg calcite skeleton in water undersaturated in regards to high-Mg calcite

Tidal Dynamics Control on Cold-Water Coral Growth: A High-Resolution Multivariable Study on Eastern Atlantic Cold-Water Coral Sites

Cold-water coral communities form complex benthic ecosystems in a distinct part of the water column. The exact processes supporting reef growth and changes with time are still partly unsolved. Recent studies have suggested a tidally driven hydraulic control of flow over topographic features as a driver for local downwelling at cold-water coral sites. This mechanism forms a link between surface and coral growth depths and is a driver of resuspension of the bottom material. Only few studies have concentrated on how these processes vary with the health status and structure of the cold-water coral occurrences. In this study, we explore the processes over tidal cycles by analysing in situ stratification, hydrography and velocity data which we then combine with local topography from seven Lophelia pertusa dominated eastern Atlantic cold-water coral sites. The “quality” of coral sites varies from thriving reefs to declining and dead coral sites. We show that living and healthy corals are concentrated at sites, where local hydrodynamics create overturning and mixing which support food supply for filter-feeding corals.

Variability of bottom carbonate chemistry over the deep coral reefs in the Florida Straits and the impacts of mesoscale processes

Abundant and diverse cold-water coral and fish communities can be found in the deep waters of the Florida Straits, which are believed to be living under suboptimal conditions impacted by increasing oceanic CO2 levels. Yet, little is known regarding the spatial–temporal variability of bottom carbonate chemistry parameters and their dynamic drivers in this area. To address this issue, we present results from numerical simulations of a coupled physical-biogeochemical model for the south Florida shelf and Florida Straits. Our exploratory analysis focuses on two well-known deep-coral habitats: Pourtalès Terrace (200–450 m) and Miami Terrace (270–600 m). Results suggest that bottom waters along the northern/western slope of the Straits are comprised primarily of the North Atlantic Central Water (NWCW) and Antarctic Intermediate Water (AAIW), driven by upwelling associated with the bottom Ekman transport of the Florida Current. Over the Pourtalès Terrace, both the meandering of the Florida Current and mesoscale eddies modulate the upwelling (downwelling) of cold (warm) waters. In contrast, Florida Current makes a sharp turn at the southern end of the Miami Terrace leading to persistent island wakes, frequent occurrences of a transient eddy, and strong upwelling of deep waters toward the platform of the terrace. Passage of the transient eddy often accompanies strong downwelling of warm waters and a return (southward) flow on top of the platform. Overall, bottom water properties including temperature (T), dissolved inorganic carbon (DIC) and total alkalinity (TA) show strong variability on weekly to monthly time-scales over entire Pourtalès Terrace and on the platform of Miami Terrac, mostly driven by physics. In deeper areas (>400 m), bottom water properties are fairly stable with both DIC and TA showing narrow ranges. Interestingly, waters over the southeastern portion of the Pourtalès Terrace show consistently warmer temperature, lower DIC, and higher TA than those on top of this terrace. The aragonite saturation state (Ω) ranges 1.2-2 on top of the Pourtalès Terrace and 1.2-1.7 both on top of Miami Terrace and on the upper slope of Pourtalès Terrace. In the deeper slope areas (>400 m), it is nearly constant at 1.2-1.3. This modeling effort suggests that remote forcing and biogeochemical processes along the transport paths, from the Gulf of Mexico to the Straits, are significant but second-order contributors to the variability of bottom carbonate chemistry. The impacts of benthic biogeochemical processes along the transit paths are not resolved.

Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins

Abstract. Thriving benthic communities were observed in the oxygen minimum zones along the southwestern African margin. On the Namibian margin, fossil cold-water coral mounds were overgrown by sponges and bryozoans, while the Angolan margin was characterized by cold-water coral mounds covered by a living coral reef. To explore why benthic communities differ in both areas, present-day environmental conditions were assessed, using conductivity–temperature–depth (CTD) transects and bottom landers to investigate spatial and temporal variations of environmental properties. Near-bottom measurements recorded low dissolved oxygen concentrations on the Namibian margin of 0–0.15 mL L−1 (≜0 %–9 % saturation) and on the Angolan margin of 0.5–1.5 mL L−1 (≜7 %–18 % saturation), which were associated with relatively high temperatures (11.8–13.2 ∘C and 6.4–12.6 ∘C, respectively). Semidiurnal barotropic tides were found to interact with the margin topography producing internal waves. These tidal movements deliver water with more suitable characteristics to the benthic communities from below and above the zone of low oxygen. Concurrently, the delivery of a high quantity and quality of organic matter was observed, being an important food source for the benthic fauna. On the Namibian margin, organic matter originated directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic matter suggested an additional mechanism of food supply. A nepheloid layer observed above the cold-water corals may constitute a reservoir of organic matter, facilitating a constant supply of food particles by tidal mixing. Our data suggest that the benthic fauna on the Namibian margin, as well as the cold-water coral communities on the Angolan margin, may compensate for unfavorable conditions of low oxygen levels and high temperatures with enhanced availability of food, while anoxic conditions on the Namibian margin are at present a limiting factor for cold-water coral growth. This study provides an example of how benthic ecosystems cope with such extreme environmental conditions since it is expected that oxygen minimum zones will expand in the future due to anthropogenic activities.

Modelling the environmental niche space and distributions of cold-water corals and sponges in the Canadian northeast Pacific Ocean

Cold-water coral and sponge (CWCS) communities are important indicators of vulnerable marine ecosystems (VMEs) and are used to delineate areas for marine conservation and fisheries management. Although the northeast Pacific region of Canada (NEPC) is notable for having unique CWCS assemblages and is the location of >80% of Canadian seamounts, the extent of potential CWCS-defined VMEs in this region is unknown. Here, we used a diverse set of environmental data layers (n=30) representing a range of bathymetric derivatives, physicochemical variables, and water column properties to assess the primary factors influencing the niche separation and potential distributions of six habitat-forming groups of CWCS in the NEPC (sponge classes: Hexactinellida, Demospongiae; coral orders: Alcyonacea, Scleractinia, Antipatharia, Pennatulacea). The primary environmental gradients that influence niche separation among CWCS are driven by total alkalinity, dissolved inorganic carbon, and dissolved oxygen. Significant niche separation among groups indicates CWCS to be primarily specialists occurring in rare habitat conditions in the NEPC. Species distribution models (SDMs) developed for each CWCS group shared severely low dissolved oxygen levels ([O2] < 0.5 ml L−1) as a top predictor for habitat suitability in the NEPC. Niche separation is further emphasized by differences in the model-predicted areas of suitable habitat among CWCS groups. Although niches varied among taxa, the general areas of high habitat suitability for multiple CWCS groups in the NEPC occurred within the 500–1400 m bottom depth range which is strongly associated with the extensive oxygen minimum zone (OMZ) characterizing this region. As a result, the largest continuous area of potential CWCS habitat occurred along the continental slope with smaller, isolated patches also occurring at several offshore seamounts that have summits that extend into OMZ depths. Our results provide insight into the factors that influence the distributions of some of the most important habitat-forming taxa in the deep ocean and create an empirical foundation for supporting cold-water coral and sponge conservation in the NEPC.

Cold-water coral communities in the Central Mediterranean: aspects on megafauna diversity, fishery resources and conservation perspectives

In the last two decades, many new living cold-water coral (CWC) sites throughout the Mediterranean basin have been discovered and investigated. As part of oceanographic cruises, using ROVs and towed cameras, and trawl and longline surveys as well as records from fishermen, a belt of CWC communities has been identified along the Apulian continental margin (Central Mediterranean). The most investigated CWC communities are those of the Santa Maria di Leuca (SML) CWC province (northern Ionian Sea) and Bari Canyon (BC) (southern Adriatic Sea). These communities are mainly structured by the habitat-former species Madrepora oculata and, to a lesser extent, by Lophelia pertusa together with Dendrophyllia cornigera, solitary species, such as Desmophyllum dianthus, black coral, such as Leiopathes glaberrima, sponges (e.g., Pachastrella monilifera, Poecillastra compressa), serpulids, boring clams and colonies of bryozoans. CWC sites are biodiversity hot-spots, that act as “Essential Fish Habitats” for commercial species and through the spill-over effect might contribute to the renewal of stocks in neighbouring fishing grounds, providing ecosystems’ goods and services. Despite their particular features, CWC areas along the Apulian slope are impacted by different anthropogenic activities. Fishermen operate close and around these areas with the aim of obtaining greater catches and sizes of commercial species. Although there are many conservation proposals for CWC habitats and a Fisheries Restricted Area established for Santa Maria di Leuca CWC province, human pressure is still very strong, due to the lack of adequate conservation measures. An effective system of monitoring, control and surveillance will be fundamental to meet the conservation objectives and to reach the Good Environmental Status as part of the Marine Strategy Framework Directive.

Predicting cold-water coral distribution in the Cap de Creus Canyon (NW Mediterranean): Implications for marine conservation planning

Predictive habitat mapping has shown great promise to improve the understanding of the spatial distribution and complexity of benthic habitats and is a valuable means to highlight species-environment relationships where field data are limited. Although spatial distribution models may represent an important step forward in science-based ecosystem management, reliable predictions are hard to obtain in deep-sea environments, mainly owing to the usual paucity of high resolution maps in these settings. The aim of this study is to apply and test different spatial models to statistically predict the distribution of two Cold-Water Coral (CWC) species (Madrepora oculata, Dendrophyllia cornigera) in the Cap de Creus Canyon (NW Mediterranean), based on high-resolution swath-bathymetry (5 m resolution) and video observations through the manned submersible JAGO (IFM-GEOMAR). Several submarine canyons host CWC communities, as the environmental conditions tend to be particularly suitable for their settlement and development. Along the Cap de Creus Canyon, presence/absence of CWC was estimated in each 5 m resolution pixel based on video imagery. Maximum Entropy (MaxEnt), General Additive Model (GAM) and Random Forest were applied to represent non-linear species-environment relationships using terrain variables derived from multibeam bathymetry (slope, rugosity, aspect, backscatter). According to the models, CWC were most likely to be found on the steep walls of the southern flank which face the head and the thalweg of the canyon, aligning with the known CWC ecology acquired from previous studies. Outputs from the three models showed similar average performances in predicting CWC distribution from the available environmental variables. Slope and aspect for Madrepora oculata, and rugosity for Dendrophyllia cornigera drive their distribution, although in some cases the three models identified different variables controlling each species. To reduce differences and associated uncertainties between model outputs, 5 m resolution ensembles were produced for the two species. As a final step, an up-scaled 50 m resolution predictive map based on the fine scale ensembles is proposed as a valuable contribution for stakeholders, which need to manage large natural areas using objective and repeatable science-based approaches.

Trophic structure of cold-water coral communities revealed from the analysis of tissue isotopes and fatty acid composition

ABSTRACTThe trophic structure of cold-water coral reef communities at two contrasting locations, the 800-m deep Belgica Mounds (Irish margin) and the 300-m deep Træna reefs (Norwegian Shelf), was investigated using stable isotope (δ13C and δ15N) and fatty-acid composition analysis. A broad range of specimens, with emphasis on (commercial) fish specie's, and organic matter sources were sampled using a variety of tools. Irrespective of the environmental and geographical setting, the δ15N values indicated that the food web encompasses roughly 1.5 to 3 trophic levels. Mobile echinoderms, i.e. sea urchins and sea stars, had highest δ15N values, indicative of a high trophic position in the food web. The fraction of bacterial fatty acids in reef fauna was generally low (<5%), indicating that enhanced bacterial production in the water column through seafloor seepage of nutrients (‘hydraulic theory’) does not form a significant energy pathway into the food web. The high fraction of algal and essential fatty acids in reef fauna and fish at both locations indicates a close coupling with surface productivity, but the transport mechanism depends on the hydrographic setting. At Træna, Calanus copepods and euphausiids form an additional link between primary production and fish, which is largely absent at Belgica Mounds. At Belgica Mounds, the reef community is primarily supported by phytodetritus, as evidenced by the high contribution of algal fatty acids in faunal tissue and seasonal chlorophyll a deposition and marine snow at the reef. The environmental setting of cold-water coral reefs influences the structure of the associated food web.

Epibenthic communities of sedimentary habitats in a NE Atlantic deep seamount (Galicia Bank)

Galicia Bank is a deep seamount included as Site of Community Importance (SCI) in the Spanish Natura 2000 Network proposal. In the present study, epibenthic assemblages of sedimentary habitats have been described, together with the main environmental factor explaining species and communities distribution. Five epibenthic assemblages have been identified. Depth was the main factor explaining assemblage distribution, and the role of sediment type, water masses, and coral framework presence is also discussed. Three assemblages are located in the summit: the shallowest one (730–770m), in the boundary between Eastern North Atlantic Central Water (ENACW) and Mediterranean Overflow Water (MOW) water masses is typified by ophiuroids and characterized by medium sands. The second assemblage (770–800m) typified by the bivalve Limopsis minuta and the solitary coral Flabellum chunii correspond with medium sands and MOW core; and the third typified by the presence of cold-water coral communities dominated by Lophelia pertusa and Madrepora oculata, also on the MOW influence. In the border of the summit, in the bank break, an assemblage located in the range 1000–1200m is dominated by the urchin Cidaris cidaris and the sponge Thenea muricata. In the flat flanks around the bank, the deepest assemblage (1400–1800m) is dominated by the holothurian Benthogone rosea, in a depth range dominated by the Labrador water (LSW) and in fine sands with highest contents of organic matter. Most of species appeared in a depth range smaller than 25% of total depth range sampled and in <10% of samples. Differential preference of species is evident in the different trophic guilds, with a higher dominance of filter-feeders in the summit and of deposit-feeders in the deepest assemblage, and have clear links with nutrient dynamics in the bank.

Gloria Knolls Slide: A prominent submarine landslide complex on the Great Barrier Reef margin of north-eastern Australia

We investigate the Gloria Knolls Slide (GKS) complex on the Great Barrier Reef margin of north-eastern Australia, the largest extant mixed carbonate-siliciclastic province in the world. Based on the most complete bathymetric and sub-bottom profile datasets available for the region, we describe the main surface and subsurface geomorphologic characteristics of this landslide complex. The GKS forms a 20km along-slope and 8km across-slope indentation in the margin, extending from 250 to 1350m depth, and involves a volume of 32km3 of sediment remobilized during three events. Three main seafloor terrains can be distinguished based on seafloor morphology: a source area, a proximal depositional area and a distal depositional area. The source area includes a main headwall scarp with a maximum height of 830m and a secondary scarp at 670m depth. The proximal depositional area is flat and smooth, and lacks debris exposed on the seafloor. The distal depositional area has a hummocky surface showing a distinctive cluster of eight knolls and over 70 small debris blocks. A dredge sample from the top of the largest knoll at a depth of 1170m reveals the presence of a cold-water coral community. In the sub-bottom profiles, the mass-transport deposits in the GKS are identified below the background sediment drape as partially confined, wedge-shaped bodies of mostly weak amplitude, transparent reflectors in the proximal depositional area; and more discontinuous and chaotic in the distal depositional area. The failed sediment slabs of the GKS were evacuated, transported and disintegrated downslope in three events following a sequential failure process spreading successively from the lower slope to the upper slope. The first event initiated at the lower slope at the depth of the secondary scarp, moved downslope and disintegrated over the basin floor leaving coherent blocks. The subsequent second and third events were responsible for the formation upslope of the main scarp in the GKS. The timing of emplacement of the first GKS event, constrained by radiometric age of fossil biota from the surface of the largest slide block, was at least before 302±19ka. The presence of alternating mixed carbonate and siliciclastic lithologies that build the slope might have played an important role as a preconditioning factor in this region. Preliminary estimations suggest that unusually large seismic events were the most likely triggering mechanism for the GKS. This work contributes to the understanding of large mass-movement deposits in mixed carbonate-siliciclastic margins and provides a useful morphologic characterization and evolutionary model for assessing its tsunamigenic potential with further numerical simulations. In addition, the discovery of a cold-water coral community on top of the largest knoll has implications for identifying similar landslide-origin cold-water coral communities on the GBR margin.

New records of cold‐water coral sites and fish fauna characterization of a potential network existing in the Mediterranean Sea

AbstractNew cold‐water coral (CWC) sites were recorded along the Apulian margin (Central Mediterranean). The species composition and depth distribution of CWCs were updated. A distribution of the CWC sites coincident with the course of the dense‐water masses that flow between the Southern Adriatic and Northern Ionian was confirmed. The faunal assemblages of five of these CWC sites were investigated and compared using experimental longlines during the spring–summer and autumn–winter seasons, between 2010 and 2014. Differences in ecological variables amongst the sites in each season were evaluated by means of a set of univariate and multivariate methods (analysis of variance, permutational multivariate analysis of variance, non‐metric multidimensional scaling). Although some differences were detected in relation to the different depths examined during spring–summer, the CWC sites showed similar features in terms of species richness and diversity as well as in the abundance of the same fish species (Galeus melastomus, Conger conger, Helicolenus dactylopterus, Merluccius merluccius, Phycis blennoides and Pagellus bogaraveo) most probably because of the distribution of adult specimens in structurally complex and heterogeneous habitats, which act as a potential ‘refuge network’ with respect to commercial fishing. The presence of maturing and mature individuals as well as post‐reproductive females indicates that these CWC sites also act as spawning areas, representing a potential ‘renewal network’ for the fish populations. The term ‘network’ used here refers to several similar subsystems (CWC sites) that play the same ecological role in a wider system (Apulian margin). These CWC communities need coherent conservation measures and management strategies according to the Ecosystem Approach to Fisheries.

A phylogenetic perspective on diversity of Galatheoidea (Munida, Munidopsis) from cold-water coral and cold seep communities in the western North Atlantic Ocean

Squat lobsters (Galatheoidea and Chirostyloidea), a diverse group of decapod crustaceans, are ubiquitous members of the deep-sea fauna. Within Galatheoidea, the genera Munida and Munidopsis are the most diverse, but accurate estimates of biodiversity are difficult due to morphological complexity and cryptic diversity. Four species of Munida and nine species of Munidopsis from cold-water coral (CWC) and cold seep communities in the northwestern Atlantic Ocean (NWA) and the Gulf of Mexico (GOM) were collected over eleven years and fifteen research cruises in order to assess faunal associations and estimate squat lobster biodiversity. Identification of the majority of specimens was determined morphologically. Mitochondrial COI sequence data, obtained from material collected during these research cruises, was supplemented with published sequences of congeners from other regions. The phylogenetic analysis of Munida supports three of the four NWA and GOM species (M. microphthalma, M. sanctipauli, and M. valida) as closely related taxa. The fourth species, Munida iris, is basal to most other species of Munida, and is closely related to M. rutllanti, a species found in the northeastern Atlantic Ocean (NEA). The majority of the nine species of Munidopsis included in our analyses were collected from chemosynthetic cold seep sites from the GOM. While seep taxa were scattered throughout the phylogenetic tree, four of these species (Munidopsis livida, M. similis, M. bermudezi, and M. species A) from the NWA and the GOM were part of a large eighteen-species clade that included species collected from Pacific Ocean chemosynthetic habitats, such as hydrothermal vents and whale falls. Shinkaia crosnieri was the sister taxon to the chemosynthetic clade, and M. livida was the most basal member of this clade. Munidopsis sp. B, an undescribed species with representative individuals collected from two GOM chemosynthetic sites, exhibited the largest genetic distance from other northern Atlantic species. Generally, intraspecific diversity was lower and patterns of haplotype diversity more simple in species of Munidopsis relative to Munida. This study puts two genera of NWA and GOM squat lobsters into a population genetic and phylogenetic context with regard to biogeography and habitat to enhance understanding of the history and evolutionary trajectories of these morphologically and ecologically diverse groups.