Cold-water Coral Lophelia Pertusa Research Articles

Turbulence affects larval vertical swimming in the cold-water coral Lophelia pertusa

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.

Distinct fine-scale variations in calcification control revealed by high-resolution 2D boron laser images in the cold-water coral Lophelia pertusa.

Coral calcification is a complex biologically controlled process of hard skeleton formation, and it is influenced by environmental conditions. The chemical composition of coral skeletons responds to calcification conditions and can be used to gain insights into both the control asserted by the organism and the environment. Boron and its isotopic composition have been of particular interest because of links to carbon chemistry and pH. In this study, we acquired high-resolution boron images (concentration and isotopes) in a skeleton sample of the azooxanthellate cold-water coral Lophelia pertusa. We observed high boron variability at a small spatial scale related to skeletal structure. This implies differences in calcification control during different stages of skeleton formation. Our data point to bicarbonate active transport as a critical pathway during early skeletal growth, and the variable activity rates explain the majority of the observed boron systematic.

Mediterranean seascape suitability for Lophelia pertusa: Living on the edge

Ecological niche modelling is used in deep-sea research to investigate the environmental preferences and potential distribution of data-poor species. We present a mesoscale assessment of Mediterranean seascape suitability for the cold-water coral Lophelia pertusa (= Desmophyllum pertusum, Linnaeus, 1758). We estimated seascape suitability and uncertainty maps using an ensemble approach of three machine-learning algorithms (Generalized Boosting Model, Random Forest, Maximum Entropy) based on environmental predictors. Bathymetry, bathymetric slope and pH were the most important predictors for the models. Overall the models reached good to excellent performance, with a very reliable prediction of the most suitable areas. In the Mediterranean Sea, L. pertusa encounters environmental settings close to its physiological limits but, despite the highly variable quality of the Mediterranean seascape, we identified high suitability areas mostly along the upper slope and at submarine canyons of the Western and Central margins. The existing MPAs do not overlap with high suitability areas, and therefore L. pertusa is only protected at the deepest fringe of its potential distribution by the implementation of the bottom trawling exclusion beyond 1000 m depth. This seascape suitability assessment may assist future research, including high-resolution modelling targeting high-suitability areas, investigation on the resilience of L. pertusa populations and development of conservation actions.

Automated Activity Estimation of the Cold-Water Coral Lophelia pertusa by Multispectral Imaging and Computational Pixel Classification

AbstractThe 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-channel RGB data. 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.

Quantification of eDNA to Map the Distribution of Cold-Water Coral Reefs

An effective management of vulnerable marine ecosystems is dependent on thorough knowledge of their location. Multibeam echo-sounders and remotely operated vehicles (ROVs) are currently used to map areas impacted by industrial activities when sensitive and vulnerable species are expected, however surveying large areas using ROVs is slow and 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 rapidly assess the distribution of CWC reefs in a region. 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 5 sites with, and 5 sites without, reefs. Lophelia pertusa eDNA was detected in all 10 deep sites examined. 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. Our dispersal model used experimentally derived values for L. pertusa eDNA decay and shedding rates in realistic temperature and salinity. Treating the eDNA as a passive particle with no active vertical or horizontal movement, we successfully modelled 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 distribution of CWC reefs growing on vertical surfaces (so called wall reefs) that are challenging to detect using traditional mapping techniques.

Effects and recovery of larvae of the cold-water coral Lophelia pertusa (Desmophyllum pertusum) exposed to suspended bentonite, barite and drill cuttings

Fossil fuel drilling operations create sediment plumes and release waste materials into the ocean. These operations sometimes occur close to sensitive marine ecosystems, such as cold-water corals. While there have been several studies on the effects of energy industry activities on adult corals, there is very little information on potential impacts to their early life history stages. Larval stages of many marine organisms, including cold-water corals use cilia as a means of feeding and swimming, and if these structures become clogged with suspended particulates, the larvae may sink and be lost to the system.The objective of this study was to understand the response of Lophelia pertusa larvae to a different drilling waste components, and assess post-exposure recovery. Larvae of two ages (eight and 21 days) were exposed to a range of concentrations of bentonite, barite and drill cuttings. Larval sensitivity was assessed using the concentration at which 50% of the larvae showed behavioral effects (EC50) or lethal effects (LC50). Larvae showed greatest sensitivity to bentonite, followed by barite and drill cuttings, and also showed age-related responses that differed among the test materials. Post exposure recovery was variable across materials, with larvae exposed to bentonite having the lowest recovery rates. Understanding the vulnerability of early life history stages to human activities can help inform management strategies to preserve reproductive capacity of important marine ecosystems.

A new species of Ophryotrocha (Annelida: Dorvilleidae) associated with the coral Lophelia pertusa (Anthozoa: Caryophylliidae)

Ophryotrocha is the most speciose genus within Dorvilleidae, with species occurring in a great variety of environments around the globe. In Brazil, records of Ophryotrocha are scarce and no specific identification is provided for any of the records. Herein we describe a new species of Dorvilleidae, Ophryotrocha zitae sp. nov. Adult and larval specimens were found in the axis of a fragment of the cold-water coral Lophelia pertusa, sampled off São Paulo’s coast, at a depth of 245 m. Both forms are described and illustrated. This new species resembles O. puerilis, O. adherens and O. eutrophila, but can be distinguished based on differences in its mandible and on chaetae shape and arrangement.

Seasonal controls on the diet, metabolic activity, tissue reserves and growth of the cold-water coral Lophelia pertusa

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.

Multiple feeding strategies observed in the cold-water coral Lophelia pertusa

AbstractCold-water coral reefs are biodiversity hotspots of the deep sea. The most dominant reef-building cold-water coral in the Atlantic is Lophelia pertusa, which builds vast and structurally complex habitats. Studying the behaviours of deep-sea species is challenging due to the technological difficulties in making prolonged observations in situ, so little is known about the behavioural ecology of this important species. Observations in laboratory studies can help to enhance our understanding of the range of behaviours these species exhibit. Here we present video evidence that the cold-water coral Lophelia pertusa is capable of producing mucus nets as part of their feeding strategy. This finding suggests that L. pertusa has a more diverse range of feeding strategies than previously thought.

Documenting deepwater habitat utilization by fishes and invertebrates associated with Lophelia pertusa on a petroleum platform on the outer continental shelf of the Gulf of Mexico using a remotely operated vehicle

Marine communities associated with oil and gas platforms beyond the continental shelf are poorly described islands of potential interaction between structure oriented and pelagic taxa. Near-bottom, biological surveys were conducted at a petroleum platform located in 305 m water depth off the coast of Louisiana between 268 m and the seabed. Surveys were performed with a remotely operated vehicle (ROV) and consisted of replicated benthic transects on all four sides of the platform extending 125 m outward from the platform. The fouling community on hard surfaces of the horizontal cross-members and verticals were surveyed using HD video and digital still images. Relative abundances of fishes were estimated using digital still images collected at regular intervals under three illumination regimes: no light, red light, and white light, while the ROV hydraulics were switched off to reduce vehicle noise. Additional surveys of fishes were conducted during day and night at the platform and at two far-field sites located 2 km and 3 km from the platform by monitoring species attracted to buckets containing an olfactory attractant. The results indicated abundant coldwater coral Lophelia pertusa present on the platform and on the surrounding rubble near the platform. The fish assemblage at the platform was dominated by American barrelfish Hyperoglyphe perciformis, greater amberjack Seriola dumerili, Darwin's slimeheads Gephyroberyx darwinii, snowy grouper Epinephelus niveatus, misty grouper Hyporthodus mystacinus, American conger Conger oceanicus and Scorpaenidae. The fish community at the farfield site was substantially different and less diverse than that observed at the platform and was dominated by king snake eels (Ophichthys rex) and Scorpaenidae. The results indicate that multiple methods and both day and night surveys are necessary to obtain a more complete picture of the biological community around platforms located on the outer continental shelf. The use of red-filtered lights and quiet surveys without hydraulic pumps on can further reduce avoidance artifacts.

Boron isotope composition of the cold-water coral Lophelia pertusa along the Norwegian margin: Zooming into a potential pH-proxy by combining bulk and high-resolution approaches

High-latitude cold-water coral reefs are particularly vulnerable to climate change due to enhanced CO2 uptake in these regions. To evaluate their physiological functioning and potential application as pH archives, we retrieved both recent and fossil samples of Lophelia pertusa along the Norwegian margin from Oslofjord (59°N), over to Trondheimsfjord, Sula and Lopphavet (70.6°N). Boron isotope analyses (δ11B) were undertaken using solution-based and laser ablation multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS; LA-ICP-MS), and secondary ion mass spectrometry (SIMS). Epi-fluorescence microscopy was employed to provide a rapid pre-screening routine for structure-specific subsampling in the coral skeleton. This integrated approach enabled us to assess heterogeneities within single specimens, as well as to investigate the role of local environmental influences including recent and past variations. All three mass spectrometry methods show substantial differences in the δ11B of the theca wall (TW) and the centres of calcification (COC's). Micro-bulk subsamples milled from the theca wall of modern specimens originating from different habitats but with comparable seawater pH (8–8.16) gave consistent δ11B values averaging 26.7 (±0.2‰, 2σ, n = 4), while COC subsamples systematically deviated towards lower B/Ca (by ~40%) and depleted δ11B values (minimum 22.7 ± 0.3‰, 2σ), implying a difference of at least 4‰ between TW and COC. SIMS and LA-ICP-MS measurements identified much larger internal heterogeneities with maximum variation of ~10‰ between the distinct skeletal structures; minimal SIMS δ11B values of ~17.3 ± 1.2‰ (2σ) were associated with the pure COC material. Our findings may be interpreted in terms of the occurrence of two main, but likely different, biomineralisation mechanisms in L. pertusa, with the COC's generally exhibiting minimal pH up-regulation, potentially supporting the use of bicarbonate in the early stages of biomineralisation. Furthermore, we highlight the potential utility of L. pertusa for palaeo-proxy studies if targeting the compositionally homogenous TW zones devoid of COC admixtures, which appear to provide highly reproducible measurements.

Niche overlap between a cold-water coral and an associated sponge for isotopically-enriched particulate food sources.

The cold-water coral Lophelia pertusa is an ecosystem engineer that builds reef structures on the seafloor. The interaction of the reef topography with hydrodynamics is known to enhance the supply of suspended food sources to the reef communities. However, the reef framework is also a substrate for other organisms that may compete for the very same suspended food sources. Here, we used the passive suspension feeder Lophelia pertusa and the active suspension feeding sponge Hymedesmia coriacea as model organisms to study niche overlap using isotopically-enriched algae and bacteria as suspended food sources. The coral and the sponge were fed with a combination of 13C-enriched bacteria/15N-enriched algae or 15N-enriched bacteria/13C-enriched algae, which was subsequently traced into bulk tissue, coral skeleton and dissolved inorganic carbon (i.e. respiration). Both the coral and the sponge assimilated and respired the suspended bacteria and algae, indicating niche overlap between these species. The assimilation rates of C and N into bulk tissue of specimens incubated separately were not significantly different from assimilation rates during incubations with co-occurring corals and sponges. Hence, no evidence for exploitative resource competition was found, but this is likely due to the saturating experimental food concentration that was used. We do not rule out that exploitative competition occurs in nature during periods of low food concentrations. Food assimilation and respiration rates of the sponge were almost an order of magnitude higher than those of the cold-water coral. We hypothesize that the active suspension feeding mode of the sponge explains the observed differences in resource uptake as opposed to the passive suspension feeding mode of the cold-water coral. These feeding mode differences may set constraints on suitable habitats for cold-water corals and sponges in their natural habitats.

Effects of suspended drill cuttings on the coral Lophelia pertusa using pulsed and continuous exposure scenarios

ABSTRACTThis study aimed at providing confidence in the predictability of the impacts of drill cuttings (DC) discharge on the cold-water coral Lophelia pertusa. L. pertusa was exposed to DC from offshore exploration in the lab with the goal to assess precautionary thresholds of effects. Two exposure scenarios with DC were tested: a long-term (LT) pulsed exposure (12 weeks, peak concentrations: 2–50 mg/L, mean concentrations: 1–25 mg/L) and a short-term (ST) continuous exposure (2.5 weeks, mean concentrations: 4–42 mg/L). After exposure, a recovery period of 16 and 4 weeks was maintained in LT and ST, respectively. While there was an assumption that DC might result in an increase in respiration, decrease in growth, enhanced mucus production, reduced fatty acid content, only a significant rise was noted in skeleton growth at DC 4 mg/L and a significant increase of mucus particulate organic carbon at 25 mg/L at end of the exposure. DC did not markedly reduce prey capture rate consecutive to DC exposure. However, the effect of DC produced an increase of coral polyp activity during exposure and a return to pre-exposure conditions after cessation of DC, and coenosarc was smothered from DC even after a long recovery period (4 weeks). Overall, a DC concentration of 10 mg/L seems to represent a threshold above which changes in coral conditions were observed however with no apparent physiological consequences for the coral within the experimental time scale.

Associations between fish and cold-water coral habitats on the Icelandic shelf

The association between fish assemblages and cold-water coral habitats was evaluated based on analysis of longline catches in the Lónsdjúp trough, SE-Iceland. In 2009 and 2010, longlines were set in locations with varying coral cover within the trough. The study site is characterised by a depression (50–100 m deep), intersected by several ridges. Colonies of the cold-water coral Lophelia pertusa and other coral species were mainly found on the ridges. Among the fifteen fish species recorded, tusk (Brosme brosme) contributed ∼80% to the total fish abundance in both surveys and their catch per unit effort was twofold greater on the ridges than in adjacent flat areas. Multivariate analyses showed differences between the structure of fish communities on and off the ridges. Constrained redundancy ordinations followed by variance partitioning revealed that the structure of the fish community varied with seabed complexity, cold-water coral coverage and geographical position. It was not possible to separate between the effects of seabed complexity and coral cover, as these were strongly correlated.

Larval Behavior and Longevity in the Cold-Water Coral Lophelia pertusa Indicate Potential for Long Distance Dispersal

The life cycle of many marine benthic species includes a pelagic larval stage that governs the connectivity between populations. Larval transport is a function of hydrodynamic and biological processes. Knowledge of how larval traits affect dispersal will increase the accuracy of biophysical models used to predict connectivity, and is of paramount importance for management and conservation. This study examines the larval traits of the cold-water coral Lophelia pertusa that forms widespread and highly diverse ecosystems in the deep ocean. We monitored development, swimming behaviour, and survival under different environmental conditions. We found that the embryonic development rate doubled when the rearing temperature was increased from normal conditions of 7–8°C to 11–12°C. Pre-competent planulae migrated vertically upwards at a speed of 0.5–0.7 mm s-1 and crossed salinity gradients with a maximum tested difference of 5 psu with no hesitation. At three weeks, planulae had a fully developed mouth and started feeding on animal derivatives, picoplankton, and possibly smaller size microalgae. Presence of food significantly altered the swimming pattern, and feeding was corroborated by direct observation. Planulae survived for up to ten months in a salinity of 25 psu, which together with the vertical migration pattern and feeding indicates that larvae may spend a period of their pelagic phase in the photic zone. After 50 days, larvae were still in a very good condition as deduced by maintained high swimming speed. Survival rate of developed planulae was on average 60% over a 3-month period, and maximum longevity was a full year, in laboratory cultures.

Assessing the living and dead proportions of cold-water coral colonies: implications for deep-water Marine Protected Area monitoring in a changing ocean.

Coral growth patterns result from an interplay of coral biology and environmental conditions. In this study colony size and proportion of live and dead skeletons in the cold-water coral (CWC) Lophelia pertusa (Linnaeus, 1758) were measured using video footage from Remotely Operated Vehicle (ROV) transects conducted at the inshore Mingulay Reef Complex (MRC) and at the offshore PISCES site (Rockall Bank) in the NE Atlantic. The main goal of this paper was to explore the development of a simple method to quantify coral growth and its potential application as an assessment tool of the health of these remote habitats. Eighteen colonies were selected and whole colony and dead/living layer size were measured. Live to dead layer ratios for each colony were then determined and analysed. The age of each colony was estimated using previously published data. Our paper shows that: (1) two distinct morphotypes can be described: at the MRC, colonies displayed a ‘cauliflower-shaped’ morphotype whereas at the PISCES site, colonies presented a more flattened ‘bush-shaped’ morphotype; (2) living layer size was positively correlated with whole colony size; (3) live to dead layer ratio was negatively correlated to whole colony size; (4) live to dead layer ratio never exceeded 0.27. These results suggest that as a colony develops and its growth rate slows down, the proportion of living polyps in the colony decreases. Furthermore, at least 73% of L. pertusa colonies are composed of exposed dead coral skeleton, vulnerable to ocean acidification and the associated shallowing of the aragonite saturation horizon, with significant implications for future deep-sea reef framework integrity. The clear visual contrast between white/pale living and grey/dark dead portions of the colonies also gives a new way by which they can be visually monitored over time. The increased use of marine autonomous survey vehicles offers an important new platform from which such a surveying technique could be applied to monitor deep-water marine protected areas in the future.

Lobophorin K, a New Natural Product with Cytotoxic Activity Produced by Streptomyces sp. M-207 Associated with the Deep-Sea Coral Lophelia pertusa.

The present article describes the isolation of a new natural product of the lobophorin family, designated as lobophorin K (1), from cultures of the marine actinobacteria Streptomyces sp. M-207, previously isolated from the cold-water coral Lophelia pertusa collected at 1800 m depth during an expedition to the submarine Avilés Canyon. Its structure was determined using a combination of spectroscopic techniques, mainly ESI-TOF MS and 1D and 2D NMR. This new natural product displayed cytotoxic activity against two human tumor cell lines, such as pancreatic carcinoma (MiaPaca-2) and breast adenocarcinoma (MCF-7). Lobophorin K also displayed moderate and selective antibiotic activity against pathogenic Gram-positive bacteria such as Staphylococcus aureus.

Interactive Effects of Ocean Acidification and Warming on Growth, Fitness and Survival of the Cold-Water Coral Lophelia pertusa under Different Food Availabilities

Cold-water corals are important bioengineers that provide structural habitat for a diverse species community. About 70% of the presently known scleractinian cold-water corals are expected to be exposed to corrosive waters by the end of this century due to ocean acidification. At the same time, the corals will experience a steady warming of their environment. Studies on the sensitivity of cold-water corals to climate change mainly concentrated on single stressors in short-term incubation approaches, thus not accounting for possible long-term acclimatisation and the interactive effects of multiple stressors. Besides, preceding studies did not test for possible compensatory effects of a change in food availability. In this study a multifactorial long-term experiment (6 months) was conducted with end-of-the-century scenarios of elevated pCO2 and temperature levels in order to examine the acclimatisation potential of the cosmopolitan cold-water coral Lophelia pertusa to future climate change related threats. For the first time multiple ocean change impacts including the role of the nutritional status were tested on L. pertusa with regard to growth, “fitness,” and survival. Our results show that while L. pertusa is capable of calcifying under elevated CO2 and temperature, its condition (fitness) is more strongly influenced by food availability rather than changes in seawater chemistry. Whereas growth rates increased at elevated temperature (+4°C), they decreased under elevated CO2 concentrations (~800 μatm). No difference in net growth was detected when corals were exposed to the combination of increased CO2 and temperature compared to ambient conditions. A 10-fold higher food supply stimulated growth under elevated temperature, which was not observed in the combined treatment. This indicates that increased food supply does not compensate for adverse effects of ocean acidification and underlines the importance of considering the nutritional status in studies investigating organism responses under environmental changes.

Physiological responses and lipid storage of the coral Lophelia pertusa at varying food density

ABSTRACTDespite the importance of the cold-water coral Lophelia pertusa to deep-sea reef ecosystem functioning, current knowledge of key physiological responses to available food resources is scarce. Scenarios with varying food density may help to understand how corals deal with seasonal variations in the dark ocean and might be used to study consequences of anthropogenic activities potentially affecting food availability. Thus, the physiological responses of L. pertusa to varying food (Artemia salina nauplii) concentration, ranging from 20% to 300% of carbon equivalent turned over by basal coral respiration, were investigated. A starvation group was also included. Measurements of respiration, growth, mucus production, and energy reserves (storage fatty acids) were performed at several time intervals over 26 weeks. In general, data showed a stronger effect of experimental time on measured responses, but no significant influence of food density treatment. In starved corals, respiration rate declined to 52% of initial respiration, while skeleton growth rate was maintained at the same rate as Artemia-fed corals throughout the investigation. Mucus production measured as the sum of dissolved organic carbon (DOC) and particulate organic carbon (POC) was also similar across food treatments, but POC production exceeded that of DOC at the highest food density. No marked effect was observed on storage fatty acids. These results confirm that L. pertusa is highly resilient to environmental conditions with suboptimal food densities over a time scale of months. Regulation of several physiological processes, including respiration and mucus production, possibly in combination with an opportunistic feeding strategy, contributed to this tolerance to maintain viable corals. Thus, it appears that L. pertusa is well adapted to life in the deep sea.

Food selectivity and processing by the cold-water coral <i>Lophelia pertusa</i>

Abstract. Cold-water corals form prominent reef ecosystems along ocean margins that depend on suspended resources produced in surface waters. In this study, we investigated food processing of 13C and 15N labelled bacteria and algae by the cold-water coral Lophelia pertusa. Coral respiration, tissue incorporation of C and N and metabolically derived C incorporation into the skeleton were traced following the additions of different food concentrations (100, 300, 1300 µg C L−1) and two ratios of suspended bacterial and algal biomass (1 : 1, 3 : 1). Respiration and tissue incorporation by L. pertusa increased markedly following exposure to higher food concentrations. The net growth efficiency of L. pertusa was low (0.08 ± 0.03), which is consistent with its slow growth rate. The contribution of algae and bacteria to total coral assimilation was proportional to the food mixture in the two lowest food concentrations, but algae were preferred over bacteria as a food source at the highest food concentration. Similarly, the stoichiometric uptake of C and N was coupled in the low and medium food treatment, but was uncoupled in the high food treatment and indicated a comparatively higher uptake or retention of bacterial carbon as compared to algal nitrogen. We argue that behavioural responses for these small-sized food particles, such as tentacle behaviour, mucus trapping and physiological processing, are more likely to explain the observed food selectivity as compared to physical–mechanical considerations. A comparison of the experimental food conditions to natural organic carbon concentrations above CWC reefs suggests that L. pertusa is well adapted to exploit temporal pulses of high organic matter concentrations in the bottom water caused by internal waves and downwelling events.