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Objective: The connectivity and genetic structuring of populations throughout a region influence a species' resilience and probability of recovery from anthropogenic impacts. By gaining a comprehensive understanding of population connectivity, more effective management can be prioritized. To assess the connectivity and population genetic structure of a common cold-water coral species, Desmophyllum pertusum (Lophelia pertusa), we performed Restriction-site Associated DNA Sequencing (RADseq) on individuals from nine sites ranging from submarine canyons off New England to the southeastern coast of the United States (SEUS) and the Gulf of Mexico (GOM). Fifty-seven individuals and 3,180 single-nucleotide polymorphisms (SNPs) were used to assess genetic differentiation. Results: High connectivity exists among populations along the SEUS, yet these populations were differentiated from those to the north off New England and in Norfolk Canyon along the North Atlantic coast of the United States, as well as those in the GOM. Interestingly, Norfolk Canyon, located just north of North Carolina, and GOM populations exhibited low levels of genetic differentiation, corroborating previous microsatellite analyses and signifying gene flow between these populations. Increasing sample sizes from existing populations and including additional sampling sites over a larger geographic range would help define potential source populations and reveal fine-scale connectivity patterns among D. pertusum populations. [ABSTRACT FROM AUTHOR]

Cold-water corals form vast reefs that are highly valuable habitats for diverse deep-sea communities. However, as the deep ocean is warming, it is essential to assess the resilience of cold-water corals to future conditions. The effects of elevated temperatures on the cold-water coral Lophelia pertusa (now named Desmophyllum pertusum) from the north-east Atlantic Ocean were experimentally investigated at the holobiont level, the coral host, and its microbiome. We show that at temperature increases of + 3 and + 5 °C, L. pertusa exhibits significant mortality concomitant with changes in its microbiome composition. In addition, a metagenomic approach revealed the presence of gene markers for bacterial virulence factors suggesting that coral death was due to infection by pathogenic bacteria. Interestingly, different coral colonies had different survival rates and, colony-specific microbiome signatures, indicating strong colony-specific variability in their response to warming waters. These results suggest that L. pertusa can only survive a long-term temperature increase of < 3 °C. Therefore, regional variations in deep-sea temperature increase should be considered in future estimates of the global distribution of cold-water corals. [ABSTRACT FROM AUTHOR]

Abstract Cold-water corals form vast reefs that are highly valuable habitats for diverse deep-sea communities. However, as the deep ocean is warming, it is essential to assess the resilience of cold-water corals to future conditions. The effects of elevated temperatures on the cold-water coral Lophelia pertusa (now named Desmophyllum pertusum) from the north-east Atlantic Ocean were experimentally investigated at the holobiont level, the coral host, and its microbiome. We show that at temperature increases of + 3 and + 5 °C, L. pertusa exhibits significant mortality concomitant with changes in its microbiome composition. In addition, a metagenomic approach revealed the presence of gene markers for bacterial virulence factors suggesting that coral death was due to infection by pathogenic bacteria. Interestingly, different coral colonies had different survival rates and, colony-specific microbiome signatures, indicating strong colony-specific variability in their response to warming waters. These results suggest that L. pertusa can only survive a long-term temperature increase of

Introduction: Cold-water coral reefs form complex benthic habitats, supporting thousands of species. The broadscale environmental tolerances of reef-forming species such as Lophelia pertusa are well studied, but small-scale differences between different reef settings have received little attention so far. The controlling factors of thriving cold-water coral reefs and how these habitats differ in terms of framework extent, coral colony morphology, and associated fauna could reveal how these benthic ecosystems formand expand. Information on the natural range of environmental fluctuations could provide a better understanding of the resilience of such ecosystems towards environmental changes. Our study aimed to elaborate small-scale forces on local hydrodynamics and oceanographic parameters at two geographically close but contrasting reef sites in mid-Norway. Methods: We investigated natural fluctuations and the seasonal variability of environmental conditions of an inshore and an offshore Lophelia-dominated reef over an annual cycle by time series monitoring of physical properties by benthic landers and water sampling for biogeochemical variables using CTD casts. Results and discussion: The flow fields at the extensive reef on the offshore Sula Ridge and a bank reef at Nord-Leksa in a fjord-system differed regarding both short-term and seasonal levels. The inshore flow field was strong and tidally driven, whereas the offshore flow field was slower with large seasonal variability. The local flow regimes and the seasonal atmospheric forcing could explain the observed seasonality of the hydrographic variables and the observed inter-annual variability in biogeochemical variables. Comparison with a flow model showed that the natural short-term and seasonal variability are driven by small-scale forcing that is not represented in model analyses. These results suggest that local hydrodynamics together with sea-floor topography control the reef extent and the morphology of cold-water coral colonies. [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 (

IntroductionCold-water coral reefs form complex benthic habitats, supporting thousands of species. The broadscale environmental tolerances of reef-forming species such as Lophelia pertusa are well studied, but small-scale differences between different reef settings have received little attention so far. The controlling factors of thriving cold-water coral reefs and how these habitats differ in terms of framework extent, coral colony morphology, and associated fauna could reveal how these benthic ecosystems form and expand. Information on the natural range of environmental fluctuations could provide a better understanding of the resilience of such ecosystems towards environmental changes. Our study aimed to elaborate small-scale forces on local hydrodynamics and oceanographic parameters at two geographically close but contrasting reef sites in mid-Norway.MethodsWe investigated natural fluctuations and the seasonal variability of environmental conditions of an inshore and an offshore Lophelia-dominated reef over an annual cycle by time series monitoring of physical properties by benthic landers and water sampling for biogeochemical variables using CTD casts.Results and discussionThe flow fields at the extensive reef on the offshore Sula Ridge and a bank reef at Nord-Leksa in a fjord-system differed regarding both short-term and seasonal levels. The inshore flow field was strong and tidally driven, whereas the offshore flow field was slower with large seasonal variability. The local flow regimes and the seasonal atmospheric forcing could explain the observed seasonality of the hydrographic variables and the observed inter-annual variability in biogeochemical variables. Comparison with a flow model showed that the natural short-term and seasonal variability are driven by small-scale forcing that is not represented in model analyses. These results suggest that local hydrodynamics together with sea-floor topography control the reef extent and the morphology of cold-water coral colonies.

Lophelia pertusa reefs are vulnerable deep‐sea ecosystems and their ecological integrity partly depends on the connectivity and availability of suitable habitat. Moreover, connectivity is a guiding principle in marine conservation planning, particularly for spatial prioritization and for the design of networks of marine protected areas. We estimated the functional seascape connectivity of L. pertusa in the Mediterranean Sea and provide a framework for prioritizing habitat areas for the species conservation. These goals were achieved by simulating transport and potential dispersal of virtual larvae using biophysical modeling and assessing habitat availability based on the suitability and spatial arrangement of the seascape and inter‐annual climatological variability. Habitat availability was estimated using a network analysis and accounting for the attributes of habitat areas (i.e., size and quality). The connectivity among Mediterranean ecoregions was weak and an increase in the frequency of climate‐driven events (e.g., dense shelf water cascading) may worsen this scenario. However, the potential exchange of larvae between patches within the same ecoregion was high, favoring populations resilience to local disturbances. The analysis of habitat availability allowed identifying important habitat areas for the connectivity of the L. pertusa including the Gulf of Lion, the Apulian and Sicily Island continental margin. Some of the habitat areas identified as important for the connectivity of the L. pertusa are exposed to intense anthropogenic pressures, that may act synergistically with climate change imposing greater challenges to species conservation. These habitat areas may be prioritized in future management and conservation actions targeting L. pertusa. [ABSTRACT FROM AUTHOR]

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]

The deep sea is amongst the most food‐limited habitats on Earth, as only a small fraction (<4%) of the surface primary production is exported below 200 m water depth. Here, cold‐water coral (CWC) reefs form oases of life: their biodiversity compares with tropical coral reefs, their biomass and metabolic activity exceed other deep‐sea ecosystems by far. We critically assess the paradox of thriving CWC reefs in the food‐limited deep sea, by reviewing the literature and open‐access data on CWC habitats. This review shows firstly that CWCs typically occur in areas where the food supply is not constantly low, but undergoes pronounced temporal variation. High currents, downwelling and/or vertically migrating zooplankton temporally boost the export of surface organic matter to the seabed, creating 'feast' conditions, interspersed with 'famine' periods during the non‐productive season. Secondly, CWCs, particularly the most common reef‐builder Desmophyllum pertusum (formerly known as Lophelia pertusa), are well adapted to these fluctuations in food availability. Laboratory and in situ measurements revealed their dietary flexibility, tissue reserves, and temporal variation in growth and energy allocation. Thirdly, the high structural and functional diversity of CWC reefs increases resource retention: acting as giant filters and sustaining complex food webs with diverse recycling pathways, the reefs optimise resource gains over losses. Anthropogenic pressures, including climate change and ocean acidification, threaten this fragile equilibrium through decreased resource supply, increased energy costs, and dissolution of the calcium‐carbonate reef framework. Based on this review, we suggest additional criteria to judge the health of CWC reefs and their chance to persist in the future. [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]

The three-dimensional (3D) structure of habitat-forming corals has profound impacts on reef ecosystem processes. Elucidating coral structural responses to the environment is therefore crucial to understand changes in these ecosystems. However, little is known of how environmental factors shape coral structure in deep and dark waters, where cold-water coral (CWC) reefs thrive. Here, we attempt to infer the influence of current flow on CWC framework architecture, using 3D scanning to quantify colony shape traits (volume compactness and surface complexity) in the reef-building CWC Desmophyllum pertusum from adjacent fjord and offshore habitats with contrasting flow regimes. We find substantial architectural variability both between and within habitats. We show that corals are generally more compact in the fjord habitat, reflecting the prevailing higher current speeds, although differences in volume compactness between fjord and offshore corals are more subtle when comparing the fjord with the more exposed side of the offshore setting, probably due to locally intensified currents. Conversely, we observe no clear disparity in coral surface complexity between habitats (despite its positive correlation with volume compactness), suggesting it is not affected by current speed. Unlike volume compactness, surface complexity is similarly variable within a single colony as it is between colonies within the same habitat or between habitats and is therefore perhaps more dependent than volume compactness on microenvironmental conditions. These findings suggest a highly plastic, trait-specific and functionally relevant structural response of CWCs to current flow and underscore the importance of multiple concurrent sources of hydrodynamic forcing on CWC growth. [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]

Fjords provide unique habitats for large cold-water coral (CWC) reefs, typically growing on sills and vertical walls. Fjord reefs are among the most thriving CWC reefs in Norway. Yet, these reefs, especially the wall reefs, are notoriously understudied. Here, we mapped the biomass, total carbon (C) stocks and C turnover (as respiration) of the reef-building coral Lophelia pertusa (syn. Desmophyllum pertusum), and dominant, large CWC reef-associated suspension feeders (the sponges Geodia barretti and Mycale lingua , the CWC Madrepora oculata and the bivalve Acesta excavata) within the Hardangerfjord, Norway. Remotely Operated Vehicle (ROV) recorded videos from wall and sill reefs were used to estimate species-specific biomass. Coupled with high resolution terrain data (2 × 2 m), predictive maps of species biomass were produced using a random forest (RF) model. The resulting biomass data were integrated with species-specific C content and C respiration rates from literature to estimate C stocks and C turnover of wall versus sill reefs. Area-specific results from the RF models reveal that wall reefs had a higher habitat suitability for all species except L. pertusa , which was more dominant on the sills. Accordingly, the wall reefs supported an up to 11 times higher biomass, C stock, and turnover for all species, except for L. pertusa , which had two-fold higher values on the sill reef. As a result, the wall reefs showed a 1.5 to 4.8 times higher total mean C turnover by dominant suspension feeders (all studied species) compared to the sill reefs. With their high C turnover and their presumably wide distribution in Norwegian fjords and globally, benthic wall reef megafauna may have a substantial, but overlooked biomass and functional role within CWC reef systems. • We provide a first insight into cold-water coral reef biomass within a fjord. • Fjordic walls may play a distinct, overlooked role as cold-water coral reef habitat. • Fjordic sill reefs have higher Lophelia pertusa biomass than the walls. • Compared to the sill, wall reefs host higher overall biomass and carbon turnover. • Some reef-associated suspension feeders may prefer walls over sill habitat. [ABSTRACT FROM AUTHOR]

This study explores microplastic and cellulosic microparticle occurrences in the NE Atlantic, focusing on the Porcupine Bank Canyon and Porcupine Seabight. Water samples from depths ranging between 605 and 2126 m and Lophelia pertusa coral samples from 950 m depth were analysed. Microparticles were detected in deep-water habitats, with concentrations varying from 2.33 to 9.67 particles L−1 in the Porcupine Bank Canyon, notably lower at greater depths. This challenges the assumption of deeper habitats solely acting as microplastic sinks. We also found evidence of microparticle adsorption and ingestion by L. pertusa. The presence of microparticles in cold-water corals underscores their vulnerability to pollutants. Furthermore, the dominance of rayon microparticles in both water and coral samples raises questions about marine pollution sources, potentially linked to terrestrial origins. This research emphasises the critical need for comprehensive exploration and conservation efforts in deep-sea environments, especially to protect vital ecosystems like L. pertusa reefs. [Display omitted] • Lower microparticle concentrations at greater depths, possibly due to hydrodynamics. • First environmental record of microparticle adsorption/ingestion by cold-water coral. • Findings highlight L. pertusa 's potential vulnerability to anthropogenic pollutants. • More cellulose-based rayon than plastic polymers in deep-water and coral samples. • Rayon predominance suggests a link to terrestrial sources, not just marine pollutants. [ABSTRACT FROM AUTHOR]

Vertical migration of marine larvae may drastically affect their dispersal, especially if they are spawned in the deep sea. Previous studies have shown that the planktonic larvae of the cold-water coral Lophelia pertusa in still water swim upwards at a speed of ca. 0.5 mm s-1 during a pre-competency period of 3–5 weeks. This behavioral trait is thought to benefit dispersion of larvae as it promotes near surface drift in relatively strong currents. In the ocean however, larvae regularly encounter turbulent water movements potentially impeding their swimming ability. With no apparent stabilizing mechanism, it may be expected that the body orientation of these larvae, and consequently their directed swimming, is sensitive to perturbation by external forces. We investigated the effects of turbulence on vertical swimming of pre-competent L. pertusa larvae by exposing them to relevant turbulence intensities within a grid-stirred tank. Larval movement and water flow were simultaneously recorded, allowing for analysis of individual larval swimming velocities. We showed that the upwards directed swimming speed generally decreased with increasing turbulence, dropping to non-significant in turbulence levels occurring near ocean boundaries. Our results do however suggest that L. pertusa larvae maintain their upwards directed swimming, albeit at reduced speed, in a major part of the water column, thus allowing them to spend part of their planktonic phase in the uppermost ocean layer. This new insight into the behavior of L. pertusa larvae in their natural environment strengthens the notion of the species as one with strong potential for long-distance dispersal. Such information is important for the understanding of L. pertusa population connectivity, and vital when developing tools for modelling of larval transport.

Despite cold-water coral (CWC) reefs being considered biodiversity hotspots, very little is known about the main processes driving their morphological development. Indeed, there is a considerable knowledge gap in quantitative experimental studies that help understand the interaction between reef morphology, near-bed hydrodynamics, coral growth, and (food) particle transport processes. In the present study, we performed a 2-month long flume experiment in which living coral nubbins were placed on a reef patch to determine the effect of a unidirectional flow on the growth and physiological condition of Lophelia pertusa. Measurements revealed how the presence of coral framework increased current speed and turbulence above the frontal part of the reef patch, while conditions immediately behind it were characterised by an almost stagnant flow and reduced turbulence. Owing to the higher current speeds that likely promoted a higher food encounter rate and intake of ions involved in the calcification process, the coral nubbins located on the upstream part of the reef presented a significantly enhanced average growth and a lower expression of stress-related enzymes than the downstream ones. Yet, further experiments would be needed to fully quantify how the variations in water hydrodynamics modify particle encounter and ion intake rates by coral nubbins located in different parts of a reef, and how such discrepancies may ultimately affect coral growth. Nonetheless, the results acquired here denote that a reef influenced by a unidirectional water flow would grow into the current: a pattern of reef development that coincides with that of actual coral reefs located in similar water flow settings. Ultimately, the results of this study suggest that at the local scale coral reef morphology has a direct effect on coral growth thus, indicating that the spatial patterns of living CWC colonies in reef patches are the result of spatial self-organisation. [ABSTRACT FROM AUTHOR]

Physiological sensitivity of cold‐water corals to ocean change is far less understood than of tropical corals and very little is known about the impacts of ocean acidification and warming on degradative processes of dead coral framework. In a 13‐month laboratory experiment, we examined the interactive effects of gradually increasing temperature and pCO2 levels on survival, growth, and respiration of two prominent color morphotypes (colormorphs) of the framework‐forming cold‐water coral Lophelia pertusa, as well as bioerosion and dissolution of dead framework. Calcification rates tended to increase with warming, showing temperature optima at ~ 14°C (white colormorph) and 10–12°C (orange colormorph) and decreased with increasing pCO2. Net dissolution occurred at aragonite undersaturation (ΩAr < 1) at ~ 1000 μatm pCO2. Under combined warming and acidification, the negative effects of acidification on growth were initially mitigated, but at ~ 1600 μatm dissolution prevailed. Respiration rates increased with warming, more strongly in orange corals, while acidification slightly suppressed respiration. Calcification and respiration rates as well as polyp mortality were consistently higher in orange corals. Mortality increased considerably at 14–15°C in both colormorphs. Bioerosion/dissolution of dead framework was not affected by warming alone but was significantly enhanced by acidification. While live corals may cope with intermediate levels of elevated pCO2 and temperature, long‐term impacts beyond levels projected for the end of this century will likely lead to skeletal dissolution and increased mortality. Our findings further suggest that acidification causes accelerated degradation of dead framework even at aragonite saturated conditions, which will eventually compromise the structural integrity of cold‐water coral reefs. [ABSTRACT FROM AUTHOR]

Corals are globally important calcifiers that exhibit complex responses to anthropogenic warming and acidification. Although coral calcification is supported by high seawater pH, photosynthesis by the algal symbionts of zooxanthellate corals can be promoted by elevated pCO2. To investigate the mechanisms underlying corals' complex responses to global change, three species of tropical zooxanthellate corals (Stylophora pistillata, Pocillopora damicornis, and Seriatopora hystrix) and one species of asymbiotic cold-water coral (Desmophyllum pertusum, syn. Lophelia pertusa) were cultured under a range of ocean acidification and warming scenarios. Under control temperatures, all tropical species exhibited increased calcification rates in response to increasing pCO2. However, the tropical species' response to increasing pCO2 flattened when they lost symbionts (i.e., bleached) under the high-temperature treatments—suggesting that the loss of symbionts neutralized the benefit of increased pCO2 on calcification rate. Notably, the cold-water species that lacks symbionts exhibited a negative calcification response to increasing pCO2, although this negative response was partially ameliorated under elevated temperature. All four species elevated their calcifying fluid pH relative to seawater pH under all pCO2 treatments, and the magnitude of this offset (Δ[H+]) increased with increasing pCO2. Furthermore, calcifying fluid pH decreased along with symbiont abundance under thermal stress for the one species in which calcifying fluid pH was measured under both temperature treatments. This observation suggests a mechanistic link between photosymbiont loss ('bleaching') and impairment of zooxanthellate corals' ability to elevate calcifying fluid pH in support of calcification under heat stress. This study supports the assertion that thermally induced loss of photosymbionts impairs tropical zooxanthellate corals' ability to cope with CO2-induced ocean acidification. [ABSTRACT FROM AUTHOR]

Seawater temperature is one of the main variables that determines cold-water coral distribution worldwide. As part of an initiative to explore new areas of deep-sea habitats along the Southeast United States (SEUS) continental margin, a series of expeditions were carried out as part of the Deep-Sea Exploration to Advance Research on Corals/Canyons/Cold seeps (DEEP SEARCH) project. During these explorations, a cold-water coral reef complex composed mainly of Lophelia pertusa was located off the coast of South Carolina at 650–850 m depth. In this geographic area the species normally has a thermal tolerance between 6 and 12 °C with the capacity to form extensive calcium carbonate structures, thus creating complex habitat for a variety of associated species. Owing to the paucity of these structures and the unusual environmental conditions of this geographic area, with regular arrival of warm surface waters from the Gulf Stream, the main aim of this study was to understand the physiological response of L. pertusa to the variation in extreme temperature events in this region. Short-term experiments simulated the rate of temperature increase from the ambient temperature (8 °C) to the environmental maximum (14 °C) (heat-wave treatment). We found that temperature had a significant effect on the metabolic functions through an increase in respiration (0.108 to 0.247 µmol O2 g−1DW h−1) and excretion rates (0.002 to 0.011 µmol NH3 g−1DW h−1) at 14 °C. Oxygen to Nitrogen ratios (O:N) also showed an effect of temperature where corals switched from lipid-dominated toward a mix of lipid-protein and protein-dominated catabolism. To further characterize the metabolic response, feeding assays (capture rate of Artemia) were performed at the same temperature range with an overall three-fold decrease in capture rates under 14 °C compared to ambient temperature, thus increasing the probability of temperature-induced metabolic stress. Our results suggest that temperature variations affect the metabolic response of cold-water corals, particularly along the SEUS continental margin. Since the incursion of warm surface water to deeper zones is predicted to increase in frequency and duration due to climate change, L. pertusa may be implicated negatively, followed by ecological consequences for the survival and functionality for the ecosystem it supports. [ABSTRACT FROM AUTHOR]

On the Tautra Ridge – a 39-100 m deep morainic sill located in the middle of the Trondheimsfjord, Norway – some of the world’s shallowest known occurrences of the scleractinian cold-water coral (CWC) Desmophyllum pertusum can be found. The earliest D. pertusum records from the Tautra Ridge date back to the 18th century, and since then, the location has provided easy access to physical coral specimens for numerous scientific studies. In 2013, the ridge was declared a marine protected area by the Norwegian Government due to its unique CWC reefs. However, few attempts have to our knowledge yet been made to characterize the distribution, extent and condition of these reefs extensively. The aim of the current study was therefore to add geospatial context to the Tautra CWC reef complex. In the study, data from multibeam echo sounding, synthetic aperture sonar imaging and underwater hyperspectral imaging are used to assess CWC reef occurrences from multiple perspectives. The study demonstrates how complementary remote sensing techniques can be used to increase knowledge generation during seafloor mapping efforts. Ultimately, predictive modeling based on seafloor geomorphometry is used to estimate both distribution and areal coverage of D. pertusum reefs along the majority of the Tautra Ridge. Our findings suggest that D. pertusum reef distribution on the Tautra Ridge is affected by several geomorphometric seafloor properties, and that the total reef extent in the area likely is close to 0.64 km2. Better description of current patterns across the Tautra Ridge will improve our understanding of the interaction between hydrography and geomorphology at the Tautra CWC reef complex in the future.

Cold-water coral (CWC) reefs are numerous and widespread along the Norwegian continental shelf where oil and gas industry operate. Uncertainties exist regarding their impacts from operational discharges to drilling. Effect thresholds obtained from near-realistic exposure of suspended particle concentrations for use in coral risk modeling are particularly needed. Here, nubbins of Desmophyllum pertusum (Lophelia pertusa) were exposed shortly (5 days, 4h repeated pulses) to suspended particles (bentonite BE; barite BA, and drill cuttings DC) in the range of ~ 4 to ~ 60 mg.l-1 (actual concentration). Physiological responses (respiration rate, growth rate, mucus-related particulate organic carbon OC and particulate organic nitrogen ON) and polyp mortality were then measured 2 and 6 weeks post-exposure to assess long-term effects. Respiration and growth rates were not significantly different in any of the treatments tested compared to control. OC production was not affected in any treatment, but a significant increase of OC:ON in mucus produced by BE-exposed (23 and 48 mg.l-1) corals was revealed 2 weeks after exposure. Polyp mortality increased significantly at the two highest DC doses (19 and 49 mg.l-1) 2 and 6 weeks post-exposure but no significant difference was observed in any of the other treatments compared to the control. These findings are adding new knowledge on coral resilience to short realistic exposure of suspended drill particles and indicate overall a risk for long-term effects at a threshold of ~20 mg.l-1. [ABSTRACT FROM AUTHOR]

Cold-water corals are threatened by global warming, especially in the Mediterranean Sea where they live close to their upper known thermal limit (i.e. 13°C), yet their response to rising temperatures is not well known. Here, temperature effects on Lophelia pertusa and Madrepora oculata holobionts (i.e. the host and its associated microbiome) were investigated. We found that at warmer seawater temperature (+2°C), L. pertusa showed a modification of its microbiome prior to a change in behaviour, leading to lower energy reserves and skeletal growth, whereas M. oculata was more resilient. At extreme temperature (+4°C), both species quickly lost their specific bacterial signature followed by lower physiological activity prior to death. In addition, our results showing the holobionts' negative response to colder temperatures (−3°C), suggest that Mediterranean corals live close to their thermal optimum. The species-specific response to temperature change highlights that global warming may affect dramatically the main deep-sea reef-builders, which would alter the associated biodiversity and related ecosystem services. [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]

Ocean warming and acidification pose serious threats to cold-water corals (CWCs) and the surrounding habitat. Yet, little is known about the role of natural short-term and seasonal environmental variability, which could be pivotal to determine the resilience of CWCs in a changing environment. Here, we provide continuous observational data of the hydrodynamic regime (recorded using two benthic landers) and point measurements of the carbonate and nutrient systems from five Lophelia pertusa reefs in the Langenuen Fjord, southwestern Norway, from 2016 to 2017. In this fjord setting, we found that over a tidal (<24 h) cycle during winter storms, the variability of measured parameters at CWC depths was comparable to the intra-annual variability, demonstrating that single point measurements are not sufficient for documenting (and monitoring) the biogeochemical conditions at CWC sites. Due to seasonal and diurnal forcing, parts of the reefs experienced temperatures up to 4 °C warmer (i.e., >12 °C) than the mean conditions and high CT concentrations of 20 μmol kg-1 over the suggested threshold for healthy CWC reefs (i.e., >2170 μmol kg-1). Combined with hindcast measurements, our findings indicate that these shallow fjord reefs may act as an early hotspot for ocean warming and acidification. We predict that corals in Langenuen will face seasonally high temperatures (>18 °C) and hypoxic and corrosive conditions within this century. Therefore, these fjord coral communities could forewarn us of the coming consequences of climate change on CWC diversity and function. [ABSTRACT FROM AUTHOR]

Hyrrokkin sarcophaga is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Desmophyllum pertusum (formerly known as Lophelia pertusa). Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupled-plasma MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr / Ca ratios are 1.1 mmol mol -1 higher in H. sarcophaga that infest D. pertusum , which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of D. pertusum has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 ‰ lower δ13 C and 0.25 ‰ lower δ18 O values in H. sarcophaga that lived on D. pertusum , which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO 2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn / Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr / Ca, Mn / Ca, δ18 O or δ13 C unless the host organism is known and its geochemical composition can be accounted for. [ABSTRACT FROM AUTHOR]

The occurrence and proliferation of reef-forming corals is of vast importance in terms of the biodiversity they support and the ecosystem services they provide. The complex three-dimensional structures engineered by corals are comprised of both live and dead coral, and the function, growth and stability of these systems will depend on the ratio of both. To model how the ratio of live: dead coral may change, the 'Goldilocks Principle' can be used, where organisms will only flourish if conditions are 'just right'. With data from particle imaging velocimetry and numerical smooth particle hydrodynamic modelling with two simple rules, we demonstrate how this principle can be applied to a model reef system, and how corals are effectively optimizing their own local flow requirements through habitat engineering. Building on advances here, these approaches can be used in conjunction with numerical modelling to investigate the growth and mortality of biodiversity supporting framework in present-day and future coral reef structures. [ABSTRACT FROM AUTHOR]

Abstract Background Numerous studies have shown that bacteria form stable associations with host corals and have focused on identifying conserved “core microbiomes” of bacterial associates inferred to be serving key roles in the coral holobiont. Because studies tend to focus on only stony corals (order Scleractinia) or soft corals (order Alcyonacea), it is currently unknown if there are conserved bacteria that are shared by both. A meta-analysis was done of 16S rRNA amplicon data from multiple studies generated via identical methodology to allow direct comparisons of bacterial associates across seven deep-sea corals, including both stony and soft species: Anthothela grandiflora, Anthothela sp., Lateothela grandiflora, Lophelia pertusa, Paramuricea placomus, Primnoa pacifica, and Primnoa resedaeformis. Results Twenty-three operational taxonomic units (OTUs) were consistently present in greater than 50% of the coral samples. Seven amplicon sequence variants (ASVs), five of which corresponded to a conserved OTU, were consistently present in greater than 30% of the coral samples including five or greater coral species. A majority of the conserved sequences had close matches with previously identified coral-associated bacteria. While known to dominate tropical and temperate coral microbiomes, Endozoicomonas were extremely rare or absent from these deep-sea corals. An Endozoicomonas OTU associated with Lo. pertusa in this study was most similar to those from shallow-water stony corals, while an OTU associated with Anthothela spp. was most similar to those from shallow-water gorgonians. Conclusions Bacterial sequences have been identified that are conserved at the level of class Anthozoa (i.e., found in both stony and soft corals, shallow and deep). These bacterial associates are therefore hypothesized to play important symbiotic roles and are highlighted for targeted future study. These conserved bacterial associates include taxa with the potential for nitrogen and sulfur cycling, detoxification, and hydrocarbon degradation. There is also some overlap with kit contaminants that need to be resolved. Rarely detected Endozoicomonas sequences are partitioned by whether the host is a stony coral or a soft coral, and the finer clustering pattern reflects the hosts’ phylogeny.

In 2003, a large Lophelia pertusa reef complex was discovered on the southeast edge of the Scotian Shelf, representing the only known cold-water coral reef in Canada. Extensive damage to the reef from bottom fishing activities was apparent, which resulted in the establishment of the 15-km2 Lophelia Coral Conservation Area (LCCA) in 2004 to prevent further damage and allow recovery. Since 2004, the effectiveness of the LCCA in achieving these objectives has never been assessed. Through the analysis of benthic images collected in 2003, 2009, and 2015, we evaluated the effectiveness of the LCCA in terms of its success in facilitating the recolonization and recovery of its target species, L. pertusa, and in conserving local benthic biodiversity. Using multivariate community analyses and generalized linear modelling techniques, we compared changes in the diversity, abundance, and composition of epibenthic megafauna within and outside its boundaries over the 12-year period. We observed an increase in epibenthic megafaunal species density and abundance over time that was higher inside the closure than outside, suggesting that the LCCA has facilitated the recruitment and recovery of the benthic communities within its confines. While recruitment of L. pertusa was low, the recent discovery of numerous undisturbed large mounds of live L. pertusa establishes a local recruitment source, a prerequisite for the reef structure to recover to its pre-disturbed state. We recommend that monitoring of the reef structure occur every 7–10 years to evaluate the settlement and growth of L. pertusa and the other deep-water corals that reside there.

The cold-water coral Lophelia pertusa builds up bioherms that sustain high biodiversity in the deep ocean worldwide. Photographic monitoring of the polyp activity represents a helpful tool to characterize the health status of the corals and to assess anthropogenic impacts on the microhabitat. Discriminating active polyps from skeletons of white Lophelia pertusa is usually time consuming and error prone due to their similarity in color in common red-green-blue (RGB) camera footage. Acquisition of finer-resolved spectral information might increase the contrast between the segments of polyps and skeletons, and therefore could support automated classification and accurate activity estimation of polyps. For recording the needed footage, underwater multispectral imaging systems can be used, but they are often expensive and bulky. Here we present results of a new, lightweight, compact, and low-cost deep-sea tunable LED-based underwater multispectral imaging system (TuLUMIS) with eight spectral channels. A branch of healthy white Lophelia pertusa was observed under controlled conditions in a laboratory tank. Spectral reflectance signatures were extracted from pixels of polyps and skeletons of the observed coral. Results showed that the polyps can be better distinguished from the skeleton by analysis of the eight-dimensional spectral reflectance signatures compared to three-channelRGBdata. During a 72-h monitoring of the coral with a half-hour temporal resolution in the laboratory, the polyp activity was estimated based on the results of the multispectral pixel classification using a support vector machine (SVM) approach. The computational estimated polyp activity was consistent with that of the manual annotation, which yielded a correlation coefficient of 0.957. [ABSTRACT FROM AUTHOR]

This study presents a novel approach resulting in the first cold-water coral reef biomass maps, used to assess associated ecosystem functions, such as carbon (C) stock and turnover. We focussed on two dominant ecosystem engineers at the Mingulay Reef Complex, the coral Lophelia pertusa (rubble, live and dead framework) and the sponge Spongosorites coralliophaga. Firstly, from combining biological (high-definition video, collected specimens), environmental (extracted from multibeam bathymetry) and ecosystem function (oxygen consumption rate values) data, we calculated biomass, C stock and turnover which can feed into assessments of C budgets. Secondly, using those values, we employed random forest modelling to predictively map whole-reef live coral and sponge biomass. The whole-reef mean biomass of S. coralliophaga was estimated to be 304 T (range 168–440 T biomass), containing 10 T C (range 5–18 T C) stock. The mean skeletal mass of the coral colonies (live and dead framework) was estimated to be 3874 T (range 507–9352 T skeletal mass), containing a mean of 209 T of biomass (range 26–515 T biomass) and a mean of 465 T C (range 60–1122 T C) stock. These estimates were used to calculate the C turnover rates, using respiration data available in the literature. These calculations revealed that the epi- and microbial fauna associated with coral rubble were the largest contributor towards C turnover in the area with a mean of 163 T C year−1 (range 149–176 T C year−1). The live and dead framework of L. pertusa were estimated to overturn a mean of 32 T C year−1 (range 4–93 T C year−1) and 44 T C year−1 (range 6–139 T C year−1), respectively. Our calculations showed that the Mingulay Reef overturned three to seven (with a mean of four) times more C than a soft-sediment area at a similar depth. As proof of concept, the supply of C needed from surface water primary productivity to the reef was inferred. Since 65–124 T C year−1 is supplied by natural deposition and our study suggested that a mean of 241 T C year−1 (range 160–400 T C year−1), was turned over by the reef, a mean of 117–176 T C year−1 (range 36–335 T C year−1) of the reef would therefore be supplied by tidal downwelling and/or deep-water advection. Our results indicate that monitoring and/or managing surface primary productivity would be a key consideration for any efforts towards the conservation of cold-water coral reef ecosystems. [ABSTRACT FROM AUTHOR]

Ocean acidification is a threat to the net growth of tropical and deep-sea coral reefs, due to gradual changes in the balance between reef growth and loss processes. Here we go beyond identification of coral dissolution induced by ocean acidification and identify a mechanism that will lead to a loss of habitat in cold-water coral reef habitats on an ecosystem-scale. To quantify this, we present in situ and year-long laboratory evidence detailing the type of habitat shift that can be expected (in situ evidence), the mechanisms underlying this (in situ and laboratory evidence), and the timescale within which the process begins (laboratory evidence). Through application of engineering principals, we detail how increased porosity in structurally critical sections of coral framework will lead to crumbling of load-bearing material, and a potential collapse and loss of complexity of the larger habitat. Importantly, in situ evidence highlights that cold-water corals can survive beneath the aragonite saturation horizon, but in a fundamentally different way to what is currently considered a biogenic cold-water coral reef, with a loss of the majority of reef habitat. The shift from a habitat with high 3-dimensional complexity provided by both live and dead coral framework, to a habitat restricted primarily to live coral colonies with lower 3-dimensional complexity represents the main threat to cold-water coral reefs of the future and the biodiversity they support. Ocean acidification can cause ecosystem-scale habitat loss for the majority of cold-water coral reefs.

An effective management of vulnerable marine ecosystems is dependent on thorough knowledge of their location. Multibeam bathymetric mapping and targeted remotely operated vehicle (ROV) surveys are currently used to map areas impacted by industrial activities when vulnerable species are expected. However, multibeam bathymetric mapping is not always a possibility and surveying large areas using ROVs is expensive. Here, we developed a species-specific eDNA assay targeting a 178 bp fragment in the control region of the mitochondrial DNA of the cold-water coral (CWC) Lophelia pertusa. The aim was to test if concentrations of L. pertusa eDNA in seawater, determined using droplet digital PCR (ddPCR) technology, could be used to assess the broad scale distribution of CWCs in a region, to supplement multibeam mapping and direct targeted ROV surveys. Our assay successfully amplified L. pertusa DNA from seawater. In laboratory we documented an exponential decay rate of the targeted DNA fragment and a linear correlation between coral biomass and eDNA concentrations in flow through microcosms. The ability of the method to detect CWC reefs in situ was tested in the fjords south of Bergen, Norway, where such reefs are common. We tested five sites with, and five sites without, known reefs. Lophelia pertusa eDNA was detected in all 10 sites. However, concentrations were elevated by 5 to 10 times in water sampled off the two large reefs growing on vertical surfaces. Water sampled 10 m above CWC reefs growing on the flat seabed did not produce an equally clear eDNA signal, nor did single CWC colonies growing on vertical surfaces. Treating the eDNA as a passive particle with no active vertical or horizontal movement, we successfully modeled the dispersal of eDNA from the known CWC reefs in the region and achieved a good fit with measured eDNA concentrations. In all, our study demonstrated a great potential for eDNA measurements as a cost-efficient tool for a rapid screening of the broad scale distribution of CWC reefs growing on vertical surfaces (so called wall reefs) that cannot be imaged using traditional ship mounted downward looking multibeam echo-sounders and difficult to detect using ROVs alone.

Cold-water corals are habitat-forming species that are also classified as indicators of vulnerable marine ecosystems (VMEs) due to the threat of various anthropogenic impacts, e.g., fisheries and oil/mineral exploration. To best protect VMEs, knowledge of their habitat requirements and distribution is essential. However, comprehensive sampling of the deep sea is difficult due to access and cost constraints, so species distribution modeling (SDM) is often used to predict overall distributions and ecological preferences of species based on limited data. We used Maximum Entropy (Maxent) modeling to predict the probability of presence of the reef-building scleractinian Lophelia pertusa and the octocorals Paragorgia arborea and Primnoa resedaeformis using a total of 2149 coral presence points and 15 environmental predictor variables. The environmental variables used in the analysis were processed to 176 m resolution and included bathymetry, depth, geomorphometric characteristics [slope, aspect, and bathymetric position index (BPI)], oceanography (temperature, salinity, current directions, and speed), surface chlorophyll a concentration, sediment type, and marine landscape type. Comparing presence points with environmental data showed that the temperature and depth range for Lophelia was narrower compared to the gorgonians, and it occurred in shallower, warmer water. Observations showed that Lophelia had a broad, bimodal response to Broad BPI, while the predicted model indicated a more narrow response. Paragorgia tolerated the greatest range of sloping according to the model. All three species were observed with a bimodal pattern along a wide range of mean current speed, while the models indicated a high response to faster current speed. Jackknife tests showed that sediment type was an important predictor for gorgonian corals, while BPI and minimum temperature were more important for Lophelia. The spatial precision of the models could be further increased by applying environmental layers with a higher and uniform spatial resolution. The predicted distribution of corals and their relation to environmental variables provides an important background for prioritizing areas for detailed mapping surveys and will aid in the conservation efforts for these VMEs in Norwegian waters and beyond.

Cold-water coral (CWC) ecosystems provide niches and nurseries for many deep-sea species. Lophelia pertusa and Madrepora oculata, two cosmopolitan species forming three dimensional structures, are found in cold waters under specific hydrological regimes that provide food and reoxygenation. There is now more information about their feeding, their growth and their associated microbiome, however, little is known about the influence of their habitat on their physiology, or on the composition of their bacterial community. The goal of this study was to test if the habitat of L. pertusa and M. oculata influenced the hosts associated bacterial communities, the corals’ survival and their skeletal growth along the slope of a submarine canyon. A transplant experiment was used, based on sampling and cross-redeployment of coral fragments at two contrasted sites, one deeper and one shallower. Our results show that M. oculata had significantly higher skeletal growth rates in the shallower site and that it had a specific microbiome that did not change between sites. Inversely, L. pertusa had the same growth rates at both sites, but its bacterial community compositions differed between locations. Additionally, transplanted L. pertusa acquired the microbial signature of the local corals. Thus, our results suggest that M. oculata prefer the shallower habitat.

Reefs formed by scleractinian cold-water corals represent unique biodiversity hot spots in the deep sea, preferring aphotic water depths of 200–1000 m. The distribution of the most prominent reef-building species Lophelia pertusa is controlled by various environmental factors including dissolved oxygen concentrations and temperature. Consequently, the expected ocean deoxygenation and warming triggered by human-induced global change are considered as a serious threat to cold-water coral reefs. Here, we present results on recently discovered reefs in the SE Atlantic, where L. pertusa thrives in hypoxic and rather warm waters. This sheds new light on its capability to adapt to extreme conditions, which is facilitated by high surface ocean productivity, resulting in extensive food supply. Putting our data in an Atlantic-wide perspective clearly demonstrates L. pertusa's ability to develop population-specific adaptations, which are up to now hardly considered in assessing its present and future distributions. [ABSTRACT FROM AUTHOR]

Cold‐water corals (CWCs) are important foundation species in the world's largest ecosystem, the deep sea. They support a rich faunal diversity but are threatened by climate change and increased ocean acidification. As part of this study, fragments from three genetically distinct Lophelia pertusa colonies were subjected to ambient pH (pH = 7.9) and low pH (pH = 7.6) for six months. RNA was sampled at two, 4.5, and 8.5 weeks and sequenced. The colony from which the fragments were sampled explained most of the variance in expression patterns, but a general pattern emerged where upregulation of ion transport, required to maintain normal function and calcification, was coincident with lowered expression of genes involved in metabolic processes; RNA regulation and processing in particular. Furthermore, there was no differential expression of carbonic anhydrase detected in any analyses, which agrees with a previously described lack of response in enzyme activity in the same corals. However, one colony was able to maintain calcification longer than the other colonies when exposed to low pH and showed increased expression of ion transport genes including proton transport and expression of genes associated with formation of microtubules and the organic matrix, suggesting that certain genotypes may be better equipped to cope with ocean acidification in the future. While these genotypes exist in the contemporary gene pool, further stresses would reduce the genetic variability of the species, which would have repercussions for the maintenance of existing populations and the ecosystem as a whole. [ABSTRACT FROM AUTHOR]

The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodiversity and distributions of deep‐sea fauna, thereby compromising key ecosystem services. Understanding how climate change can lead to shifts in deep‐sea species distributions is critically important in developing management measures. We used environmental niche modelling along with the best available species occurrence data and environmental parameters to model habitat suitability for key cold‐water coral and commercially important deep‐sea fish species under present‐day (1951–2000) environmental conditions and to project changes under severe, high emissions future (2081–2100) climate projections (RCP8.5 scenario) for the North Atlantic Ocean. Our models projected a decrease of 28%–100% in suitable habitat for cold‐water corals and a shift in suitable habitat for deep‐sea fishes of 2.0°–9.9° towards higher latitudes. The largest reductions in suitable habitat were projected for the scleractinian coral Lophelia pertusa and the octocoral Paragorgia arborea, with declines of at least 79% and 99% respectively. We projected the expansion of suitable habitat by 2100 only for the fishes Helicolenus dactylopterus and Sebastes mentella (20%–30%), mostly through northern latitudinal range expansion. Our results projected limited climate refugia locations in the North Atlantic by 2100 for scleractinian corals (30%–42% of present‐day suitable habitat), even smaller refugia locations for the octocorals Acanella arbuscula and Acanthogorgia armata (6%–14%), and almost no refugia for P. arborea. Our results emphasize the need to understand how anticipated climate change will affect the distribution of deep‐sea species including commercially important fishes and foundation species, and highlight the importance of identifying and preserving climate refugia for a range of area‐based planning and management tools. [ABSTRACT FROM AUTHOR]

Cold-water coral (CWC) ecosystems provide niches and nurseries for many deep-sea species. Lophelia pertusa and Madrepora oculata , two cosmopolitan species forming three dimensional structures, are found in cold waters under specific hydrological regimes that provide food and reoxygenation. There is now more information about their feeding, their growth and their associated microbiome, however, little is known about the influence of their habitat on their physiology, or on the composition of their bacterial community. The goal of this study was to test if the habitat of L. pertusa and M. oculata influenced the hosts associated bacterial communities, the corals' survival and their skeletal growth along the slope of a submarine canyon. A transplant experiment was used, based on sampling and cross-redeployment of coral fragments at two contrasted sites, one deeper and one shallower. Our results show that M. oculata had significantly higher skeletal growth rates in the shallower site and that it had a specific microbiome that did not change between sites. Inversely, L. pertusa had the same growth rates at both sites, but its bacterial community compositions differed between locations. Additionally, transplanted L. pertusa acquired the microbial signature of the local corals. Thus, our results suggest that M. oculata prefer the shallower habitat. [ABSTRACT FROM AUTHOR]

There are numerous studies highlighting the impacts of direct and indirect stressors on marine organisms, and multi-stressor studies of their combined effects are an increasing focus of experimental work. Lophelia pertusa is a framework-forming cold-water coral that supports numerous ecosystem services in the deep ocean. These corals are threatened by increasing anthropogenic impacts to the deep-sea, such as global ocean change and hydrocarbon extraction. This study implemented two sets of experiments to assess the effects of future conditions (temperature: 8 °C and 12 °C, pH: 7.9 and 7.6) and hydrocarbon exposure (oil, dispersant, oil + dispersant combined) on coral health. Phenotypic response was assessed through three independent observations of diagnostic characteristics that were combined into an average health rating at four points during exposure and recovery. In both experiments, regardless of environmental condition, average health significantly declined during 24-hour exposure to dispersant alone but was not significantly altered in the other treatments. In the early recovery stage (24 hours), polyp health returned to the pre-exposure health state under ambient temperature in all treatments. However, increased temperature resulted in a delay in recovery (72 hours) from dispersant exposure. These experiments provide evidence that global ocean change can affect the resilience of corals to environmental stressors and that exposure to chemical dispersants may pose a greater threat than oil itself. [ABSTRACT FROM AUTHOR]

Vast cold-water coral (CWC) reefs occur in temperate regions, where strong seasonality in temperature and light leads to a short but highly productive spring period. How CWCs respond physiologically to this strong seasonal forcing remains unclear, due to the remoteness of their deep-sea habitats. In an in situ transplantation study at Nakken reef, Norway, we investigated a full seasonal cycle of (1) temperature and food availability, (2) diet, (3) biomass and tissue reserves, (4) oxygen consumption and (5) linear growth of the reef-building coral Lophelia pertusa. All investigated variables showed a distinct seasonality. An increase in the organic carbon and amino acid content, linear extension and budding rate from February to late May, at a simultaneous increase in phytoplankton and zooplankton fatty acid trophic markers (FATMs), and δ15N-derived trophic level, indicates an efficient exploitation of the spring phytoplankton and the subsequent zooplankton bloom. A pool of neutral-lipid-derived fatty acids, indicative of energy storage and gametogenesis, was formed from May to October, accompanied by increased oxygen consumption, i.e. metabolic activity. In late autumn and early winter (October–December), tissue reserves were maintained, in spite of low sPOM and zooplankton food availability, and the lower tissue δ13C and higher contribution of bacterial FATMs suggest increased reliance on more degraded material. The concurrent reduction in linear growth further suggests a lower energy availability at this time of the year. A large (> 50%) drop of all tissue pools between December and February coincided with the spawning season of L. pertusa and demonstrates a high energetic cost of reproduction. Our results show for the first time a strong seasonal control of critical life history traits such as growth patterns and timing of reproduction in this prominent deep-sea species. [ABSTRACT FROM AUTHOR]

Cold-water corals (CWC), dominantly Desmophyllum pertusum (previously Lophelia pertusa), and their mounds have been in the focus of marine research during the last two decades; however, little is known about the mound-forming capacity of other CWC species. Here, we present new 230Th/U age constraints of the relatively rarely studied framework-building CWC Solenosmilia variabilis from a mound structure off the Brazilian margin combined with computed tomography (CT) acquisition. Our results show that S. variabilis can also contribute to mound formation, but reveal coral-free intervals of hemipelagic sediment deposits, which is in contrast to most of the previously studied CWC mound structures. We demonstrate that S. variabilis only occurs in short episodes of < 4 kyr characterized by a coral content of up to 31 vol%. In particular, it is possible to identify distinct clusters of enhanced aggradation rates (AR) between 54 and 80 cm ka−1. The determined AR are close to the maximal growth rates of individual S. variabilis specimens, but are still up to one order of magnitude smaller than the AR of D. pertusum mounds. Periods of enhanced S. variabilis AR predominantly fall into glacial periods and glacial terminations that were characterized by a 60–90 m lower sea level. The formation of nearby D. pertusum mounds is also associated with the last glacial termination. We suggest that the short-term periods of coral growth and mound formation benefited from enhanced organic matter supply, either from the adjacent exposed shelf and coast and/or from enhanced sea-surface productivity. This organic matter became concentrated on a deeper water-mass boundary between South Atlantic Central Water and the Antarctic Intermediate Water and may have been distributed by a stronger hydrodynamic regime. Finally, periods of enhanced coral mound formation can also be linked to advection of nutrient-rich intermediate water masses that in turn might have (directly or indirectly) further facilitated coral growth and mound formation. [ABSTRACT FROM AUTHOR]

Along the Norwegian coasts and margins, extensive reefs of the stony coral Lophelia pertusa act as hotspots for local biodiversity. Climate models project that the temperature of Atlantic deep waters could rise by 1–3°C by 2100. In this context, understanding the effects of temperature on the physiology of cold-water species will help in evaluating their resilience to future oceanic changes. We investigated the response of L. pertusa to stepwise short-term increases in temperature. We sampled corals from four reefs, two located north of the Arctic circle and two at the mid-Norwegian shelf (boreal). In on-board experiments (one per reef), the sampled fragments were exposed to increasing temperatures from 5 to 15°C over 58 h. Respiration increased linearly by threefold for a 10°C increase. The short-term temperature increase did not induce mortality, cellular (neutral red assay for lysosome membrane stability; but one exception) or oxidative stress (lipid peroxidation assay) – to a few exceptions. However, the variability of the respiration responses depended on the experiment (i.e., reef location), possibly linked to the genetic structure of the individuals that we sampled (e.g., clones or siblings). The corals from the Arctic and boreal regions appear to have a high tolerance to the rapid temperature fluctuations they experience in the field. Over extended periods of time however, an increased metabolism could deplete the energy stored by the corals, if not met by an increased food availability and/or uptake. Empirical data on organisms' thermal performance curves, such as the one presented in this study for L. pertusa , will be useful to implement predictive models on the responses of species and populations to climate change. [ABSTRACT FROM AUTHOR]

Summary: Different cold‐water coral (CWC) species harbour distinct microbial communities and the community composition is thought to be linked to the ecological strategies of the host. Here we test whether diet shapes the composition of bacterial communities associated with CWC. We compared the microbiomes of two common CWC species in aquaria, Lophelia pertusa and Madrepora oculata, when they were either starved, or fed respectively with a carnivorous diet, two different herbivorous diets, or a mix of the 3. We targeted both the standing stock (16S rDNA) and the active fraction (16S rRNA) of the bacterial communities and showed that in both species, the corals' microbiome was specific to the given diet. A part of the microbiome remained, however, species‐specific, which indicates that the microbiome's plasticity is framed by the identity of the host. In addition, the storage lipid content of the coral tissue showed that different diets had different effects on the corals' metabolisms. The combined results suggest that L. pertusa may be preying preferentially on zooplankton while M. oculata may in addition use phytoplankton and detritus. The results cast a new light on coral microbiomes as they indicate that a portion of the CWC's bacterial community could represent a food influenced microbiome. [ABSTRACT FROM AUTHOR]

The article presents the trophic strategy and bleaching resistance in reef-building corals. Topics include the major environmental changes is understanding corals' resistance to bleaching is as crucial as it is challenging, the framework for inferring corals' trophic strategies from Stable Isotope Bayesian Ellipses has been proposed to this end, and the risk of bias inherent in its application and propose three alternative adjustments.