Food web structure and trophic interactions at the recently discovered deep-sea La Scala hydrothermal vent field (SW Pacific).

editorial reviewedHydrothermal vents are features of the seafloor where fluids (acidic, geothermally heated water enriched in chemical compounds such as hydrogen sulphide) discharge in the water column. These fluid emissions sustain unusual chemosynthesis-based ecosystems where abundant micro-organisms and animal communities can thrive under extreme conditions. In May 2019, the La Scala vent field was discovered in Woodlark Basin (Papua New Guinea, SW Pacific). Several active "black smokers" harbouring dense fauna were found at depths ranging from 3300 to 3400 m. The main engineer species were symbiont-bearing gastropods Ifremeria nautilei and Alviniconcha spp. in more active diffuse areas, and stalked barnacles Vulcanolepas sp. nov. in mildly active areas. At least 44 taxa were observed in these habitats. Here, we used trophic markers (stable isotope ratios of C, N and S) to identify energy fluxes supporting those communities, and understand how their feeding habits could influence interspecific interactions. Most sampled animals primarily depended (either directly or indirectly) on endogenous chemosynthetic vent production for their nutrition. This dependence spanned all sampled taxonomic and functional groups. It extended to organisms considered as peripheral fauna, or not strictly found at vents, such as Vulcanolepas sp. nov., anemones, or scavenging gastropods. Moreover, other peripheral fauna fed on a mix of both chemosynthesis- and photosynthesis-derived items. This emphasizes the importance of exported vent production for the surrounding deep-sea fauna. Animal communities showed considerable trophic diversity, and depended on several bacterial production mechanisms. Many taxa co-relied on two or more carbon sources, and inter- and intra-taxon differences in feeding habits could lead to a more even segregation of available food resources. While many questions about environmental and biological drivers of food web structure at La Scala vent field remain open, our results constitute a first glimpse at processes shaping those freshly discovered communities

Food web structure and trophic interactions at the recently discovered deep-sea La Scala hydrothermal vent field (SW Pacific)

editorial reviewedHydrothermal vents are features of the seafloor where fluids (acidic, geothermally heated water enriched in chemical compounds such as hydrogen sulphide) discharge in the water column. These fluid emissions sustain unusual chemosynthesis-based ecosystems where abundant micro-organisms and animal communities can thrive under extreme conditions. In May 2019, the La Scala vent field was discovered in Woodlark Basin (Papua New Guinea, SW Pacific). Several active "black smokers" harbouring dense fauna were found at depths ranging from 3300 to 3400 m. The main engineer species were symbiont-bearing gastropods Ifremeria nautilei and Alviniconcha spp. in more active diffuse areas, and stalked barnacles Vulcanolepas sp. nov. in mildly active areas. At least 44 taxa were observed in these habitats. Here, we used trophic markers (stable isotope ratios of C, N and S) to identify energy fluxes supporting those communities, and understand how their feeding habits could influence interspecific interactions. Most sampled animals primarily depended (either directly or indirectly) on endogenous chemosynthetic vent production for their nutrition. This dependence spanned all sampled taxonomic and functional groups. It extended to organisms considered as peripheral fauna, or not strictly found at vents, such as Vulcanolepas sp. nov., anemones, or scavenging gastropods. Moreover, other peripheral fauna fed on a mix of both chemosynthesis- and photosynthesis-derived items. This emphasizes the importance of exported vent production for the surrounding deep-sea fauna. Animal communities showed considerable trophic diversity, and depended on several bacterial production mechanisms. Many taxa co-relied on two or more carbon sources, and inter- and intra-taxon differences in feeding habits could lead to a more even segregation of available food resources. While many questions about environmental and biological drivers of food web structure at La Scala vent field remain open, our results constitute a first glimpse at processes shaping those freshly discovered communities

Combined in situ niche analysis and pulse-chase labelling experiments unravel energy acquisition strategies in cold-water corals

editorial reviewedCold-water corals (CWCs) are reef-building foundation species occurring worldwide in the aphotic zone of the ocean. Those reefs are considered biodiversity hotspots in the deep-sea. In the absence of endogenous production, CWCs mostly depend on exported photosynthetic production for their nutrition. Energy acquisition is therefore a major challenge for CWCs. In this context, we investigated feeding habits of three syntopic CWC species forming reefs in the Lampaul Canyon (Bay of Biscay) at depths ranging from 800 to 1200 m: Desmophyllum pertusum, Madrepora oculata and Solenosmilia variabilis. Specifically, we tackled the following questions: 1) What is the realized trophic niche of CWCs in the Lampaul Canyon?; 2) Do the three species rely on the same resources?; and 3) Are the trophic niches of CWCs overlapping with those of associated fauna, particularly suspension feeders? Joint carbon, nitrogen and sulfur stable isotope analysis showed that CWC exhibit marked resource segregation with associated fauna. However, coral niches largely overlapped. Species-specific trends in niche size were present, suggesting variable trophic diversity. Fatty acid analysis highlighted the importance of zooplankton for CWC feeding, which could favor this resource for its high nutritional value. Furthermore, pulse-chase experiments in pressurized tanks suggested that all species are, to some extent, able to function as holobionts. They notably obtain part of their nitrogen from mutualistic relationships with the microbiome living in the mucus secreted by the polyps. Ultimately, reliance upon these multiple, non-mutually exclusive ecological mechanisms could be a key factor to facilitate CWCs future survival under changing environmental conditions