The deep-sea corals Dendrophyllia ramea and Dendrophyllia cornigera occur in Mediterranean and Atlantic waters. Both species are found in different environmental conditions, and they can colonize hard and soft substrates. These species then display an important ecological plasticity along with morphological plasticity. Nevertheless, there is a large knowledge gap on the genetic characteristics of the two species, including on the relationships between them and the possibility of cryptic species along their range. The recent discovery of Dendrophyllia populations off Cyprus in the eastern Mediterranean Sea raised new questions in this context. These corals were related to D. ramea but had some morphological differences with other known populations of this species. Here, we study the specific status of Dendrophyllia corals from Cyprus on the basis of morphology and genetics. The genetic data are interpreted by comparison with the same analysis performed on two Caryophyllia species. Both morphological and genetic data confirm that corals found off Cyprus belong to the D. ramea species. We further tested the speciation scenario using transcriptome data: the results indicate an absence of current gene flow between D. ramea and D. cornigera and that the divergence occurred more than 3 million years ago. We discuss the possible historical and ecological factors which may have shaped speciation in these species.

Many cold-water sponges harbour microorganisms of which the role in the sponge host remains enigmatic. Here, we show a transfer of fixed inorganic carbon by sponge-associated microbes to its host, the cold-water coral encrusting sponge Hymedesmia (Stylopus) coriacea. Sponge were collected at approx. 100 m depth and incubated for 1.5-2.5 days with C-13 labelled dissolved inorganic carbon (DIC) as tracer. Total DIC fixation rates ranged from 0.03-0.11 mmol C x mmol C-sponge x d(-1). C-13-tracer was recovered in bacterial-specific (i.e. short and branched) and sponge-specific (very long-chained) phospholipid-derived fatty acids (PLFA's), but was not incorporated into archaeal lipids. C-13-incorporation in biomarkers such as C16:1w7c and C18:1w7c indicated that nitrifying and/or sulphur-oxidizing bacteria (chemoautotrophs) were likely active in the sponge. Trophic transfer of microbially-fixed carbon to the sponge host was confirmed by recovery of label in very long chain fatty acids (VLCFA's) including C26:2 and C26:3. Tracer accumulation into several VLCFA's continued after removal of C-13-DIC, while tracer in most bacteria-specific PLFA's declined, indicating a transfer and elongation of bacterial-specific PLFA's to sponge-specific PLFA's. This implies that PLFA precursors released from chemo- as well as heterotrophic microbes in sponges contributed to the synthesis of VLCFA's, identifying sponge-associated bacteria as symbionts of the sponge.

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

The largest coherent cold-water coral (CWC) mound province in the Atlantic Ocean exists along the Mauritanian margin, where up to 100 m high mounds extend over a distance of similar to 400 km, arranged in two slope-parallel chains in 400-550 m water depth. Additionally, CWCs are present in the numerous submarine canyons with isolated coral mounds being developed on some canyon flanks. Seventy-seven Uranium-series coral ages were assessed to elucidate the timing of CWC colonisation and coral mound development along the Mauritanian margin for the last similar to 120,000 years. Our results show that CWCs were present on the mounds during the Last Interglacial, though in low numbers corresponding to coral mound aggradation rates of 16 cm kyr(-1). Most prolific periods for CWC growth are identified for the last glacial and deglaciation, resulting in enhanced mound aggradation (>1000 cm kyr(-1)), before mound formation stagnated along the entire margin with the onset of the Holocene. Until today, the Mauritanian mounds are in a dormant state with only scarce CWC growth. In the canyons, live CWCs are abundant since the Late Holocene at least. Thus, the canyons may serve as a refuge to CWCs potentially enabling the observed modest re-colonisation pulse on the mounds along the open slope. The timing and rate of the pre-Holocene coral mound aggradation, and the cessation of mound formation varied between the individual mounds, which was likely the consequence of vertical/lateral changes in water mass structure that placed the mounds near or out of oxygen-depleted waters, respectively. (C) 2018 The Authors. Published by Elsevier Ltd.

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.

This study demonstrates how cold-water coral morphology and habitat distribution are shaped by local hydrodynamics, using high-definition video from Tisler Reef, an inshore reef in Norway. A total of 334 video frames collected on the north-west (NW) and south-east (SE) side of the reef were investigated for Lophelia pertusa coral cover and morphology and for the cover of the associated sponges Mycale lingua and Geodia sp. Our results showed that the SE side was a better habitat for L. pertusa (including live and dead colonies). Low cover of Geodia sp. was found on both sides of Tisler Reef. In contrast, Mycale lingua had higher percentage cover, especially on the NW side of the reef. Bush-shaped colonies of L. pertusa with elongated branches were the most abundant coral morphology on Tisler Reef. The highest abundance and density of this morphology were found on the SE side of the reef, while a higher proportion of cauliflower-shaped corals with short branches were found on the NW side. The proportion of very small L. pertusa colonies was also significantly higher on the SE side of the reef. The patterns in coral spatial distribution and morphology were related to local hydrodynamics-there were more frequent periods of downwelling currents on the SE side-and to the availability of suitable settling substrates. These factors make the SE region of Tisler Reef more suitable for coral growth. Understanding the impact of local hydrodynamics on the spatial extent and morphology of coral, and their relation to associated organisms such as sponges, is key to understanding the past and future development of the reef.

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.

Cold-water coral reefs form spectacular and highly diverse ecosystems in the deep sea but little is known about reproduction, and virtually nothing about the larval biology in these corals. This study is based on data from two locations of the North East Atlantic and documents the first observations of embryogenesis and larval development in Lophelia pertusa, the most common framework-building cold-water scleractinian. Embryos developed in a more or less organized radial cleavage pattern from ∼ 160 µm large neutral or negatively buoyant eggs, to 120-270 µm long ciliated planulae. Embryogenesis was slow with cleavage occurring at intervals of 6-8 hours up to the 64-cell stage. Genetically characterized larvae were sexually derived, with maternal and paternal alleles present. Larvae were active swimmers (0.5 mm s(-1)) initially residing in the upper part of the water column, with bottom probing behavior starting 3-5 weeks after fertilization. Nematocysts had developed by day 30, coinciding with peak bottom-probing behavior, and possibly an indication that larvae are fully competent to settle at this time. Planulae survived for eight weeks under laboratory conditions, and preliminary results indicate that these planulae are planktotrophic. The late onset of competency and larval longevity suggests a high dispersal potential. Understanding larval biology and behavior is of paramount importance for biophysical modeling of larval dispersal, which forms the basis for predictions of connectivity among populations.

Reefs of the cold-water coral Lophelia pertusa form biodiversity-rich habitats in the deep ocean, but physiology, reproduction, feeding and growth in this species remain poorly investigated. Food supply to reef sites varies considerably both spatially and temporarily. In this study we investigated the effects of starvation and zooplankton feeding on respiration and growth of L. pertusa. In our first experiment, corals were starved for 6 mo, resulting in a 40% decrease in respiration but no visible effects on coral condition or survival. In a second experiment, corals were fed nauplii of Artemia salina for 15 wk at 4 different densities; the organic carbon provided corresponded to between 20 and 300% of the carbon turned over by initial respiration. Respiration rate increased with zooplankton food density, but no effect on skeletal growth could be detected. Skeletal growth remained positive even at low food density. Compared to initial conditions, there was a general decrease in the total concentrations of both structural and storage fatty acids independent of food treatment, but no significant effect among the treatments was discovered. The amount of organic carbon and nitrogen also decreased during the experiment, although significantly less in the highest food density compared to the lowest. The results indicate that L. pertusa is highly tolerant to living on minimal resources for periods of several months. Response-times to varying food conditions were slow, but results suggest that tissue content and composition is a better indicator of food conditions in L. pertusa compared to calcification rates.

The aim of this study was to contribute to a general understanding of the response of the Antarctic macrobenthos to environmental variability and climate-induced changes. The change in population size of selected macrobenthic organisms was investigated in the Larsen A area east of the Antarctic Peninsula in 2007 and 2011 using ROV-based imaging methods. The results were complemented by data from the Larsen B collected in 2007 to allow a conceptual reconstruction of the environment-driven changes before the period of investigation. Both Larsen areas are characterised by ice-shelf disintegration in 1995 and 2002, respectively, as well as high inter-annual variability in sea-ice cover and oceanographic conditions. In 2007 one ascidian species, Molgula pedunculata, was abundant north and south of the stripe of remaining ice shelf between Larsen A and B. Population densities decreased drastically in the Larsen A between 2007 and 2011, coincident with the decrease in Corella eumyota, another ascidian. Among the ophiuroids, the population of deposit feeders increased, while suspension feeders halved their abundance. Current measurements indicated a northward flow between the Larsen B and Larsen A, suggesting that a major physical forcing on benthic population development comes from the South. The results demonstrate that Antarctic macrobenthic populations can exhibit dramatic population dynamics. Analyses of sea-ice dynamics, salinity, temperature and surprisingly ice-shelf disintegration history, however, did not provide any clear evidence for environmental drivers underlying the apparent changes.

Over 30% of the Antarctic continental shelf is permanently covered by floating ice shelves [1], providing aphotic conditions [2, 3] for a depauperate fauna sustained by laterally advected food [4, 5]. In much of the remaining Antarctic shallows (<300 m depth), seasonal sea-ice melting allows a patchy primary production supporting rich megabenthic communities [6, 7] dominated by glass sponges (Porifera, Hexactinellida) [8-10]. The catastrophic collapse of ice shelves due to rapid regional warming along the Antarctic Peninsula in recent decades [11] has exposed over 23,000 km(2) of seafloor to local primary production [12]. The response of the benthos to this unprecedented flux of food [13] is, however, still unknown. In 2007, 12 years after disintegration of the Larsen A ice shelf, a first biological survey interpreted the presence of hexactinellids as remnants of a former under-ice fauna with deep-sea characteristics [14]. Four years later, we revisited the original transect, finding 2- and 3-fold increases in glass sponge biomass and abundance, respectively, after only two favorable growth periods. Our findings, along with other long-term studies [15], suggest that Antarctic hexactinellids, locked in arrested growth for decades [8, 16], may undergo boom-and-bust cycles, allowing them to quickly colonize new habitats. The cues triggering growth and reproduction in Antarctic glass sponges remain enigmatic.

We investigated the interactions between the cold-water coral Lophelia pertusa and its associated polychaete Eunice norvegica by quantifying carbon (C) and nitrogen (N) budgets of tissue assimilation, food partitioning, calcification and respiration using 13C and 15N enriched algae and zooplankton as food sources. During incubations both species were kept either together or in separate chambers to study the net outcome of their interaction on the above mentioned processes. The stable isotope approach also allowed us to follow metabolically derived tracer C further into the coral skeleton and therefore estimate the effect of the interaction on coral calcification. Results showed that food assimilation by the coral was not significantly elevated in presence of E. norvegica but food assimilation by the polychaete was up to 2 to 4 times higher in the presence of the coral. The corals kept assimilation constant by increasing the consumption of smaller algae particles less favored by the polychaete while the assimilation of Artemia was unaffected by the interaction. Total respiration of tracer C did not differ among incubations, although E. norvegica enhanced coral calcification up to 4 times. These results together with the reported high abundance of E. norvegica in cold-water coral reefs, indicate that the interactions between L. pertusa and E. norvegica can be of high importance for ecosystem functioning.

The Tisler cold-water coral reef is a 2 km long reef in the north-eastern Skagerrak, Norway. The reef is comprised principally of Lophelia pertusa at depths between 70 and 160 m. Velocity shear and boundary layer shear stresses have been measured at Tisler Reef to quantify the effect of the reef structure on the benthic boundary layer (BBL) dynamics.Two different approaches to estimating the magnitude of the near seabed stress were employed: using a log-arithmic (constant stress) boundary layer approach and direct Reynolds stress measurements. Resultant estimates of near seabed stresses using both methods were comparable.Using the logarithmic layer approach to estimate seabed stresses both inside and out of the reef structure demonstrated that, for any particular impinging flow strength, higher shear stresses were observed within the live coral region than in the dead coral rubble region with no live coral stands. Bottom shear stresses of up to 3.5 N M-2 were measured within the reef complex and 1.2 N M-2 in the rubble region outside the live reef. This difference is due to large roughness length scales inside the rough living coral area relative to the smaller scales in the coral rubble.Low frequency acoustic backscatter data, used as a proxy for relative suspended particulate matter concentrations, suggested that both local re-suspension and advection of suspended material most likely occur at, and through, the reef system. The high stresses measured inside the living reef may favour corals by increasing the degree of re-suspension for a given current speed and providing more particulates to the filter feeding polyps. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.

Cold-water coral (CWC) reefs are recognised as an important marine benthic eco system at continental margins. Where abundant, they most likely play a role both in the maintenance of biodiversity and in the provision of ecosystem services provided by shelf seas. Here, we directly measure the community respiration of a CWC reef on the Norwegian shelf and show that rates of oxygen uptake are high in summer (25-88 mmol O-2 m(-2) d(-1)), with lower spring values (7.5-9 mmol O-2 m(-2) d(-1)). Spring uptake rates are comparable to values at shelf sediments at similar water depths, while summer values are much higher. We calculate that with such high respiration rates, CWC reef ecosystems potentially turnover a significant proportion (similar to 25%) of the annual shelf carbon export in the Norwegian Sea, where CWC reefs are abundant. The loss of CWCs through physical destruction or ocean acidification may have a significant impact on local carbon cycling in the mid-to high-latitude North Atlantic Ocean.