Abstract
BackgroundNematodes are an important component of deep-sea hydrothermal vent communities, but only few nematode species are able to cope to the harsh conditions of the most active vent sites. The genus Oncholaimus is known to tolerate extreme geothermal conditions and high sulphide concentrations in shallow water hydrothermal vents, but it was only occasionally reported in deep-sea vents. In this study, we performed morphological, genetic and ecological investigations (including feeding strategies) on an abundant species of Oncholaimus recently discovered at Lucky strike vent field on the Mid-Atlantic Ridge at 1700 m water depth.ResultsWe described this species as Oncholaimus dyvae sp. nov.. This new species differs from all other members of the genus by the combination of the following characters: body length (up to 9 mm), the presence of a long spicule (79 μm) with a distally pointed end, a complex pericloacal setal ornamentation with one precloacal papilla surrounded by short spines, and a body cuticule with very fine striation shortly posterior to the amphid opening. Overall, O. dyvae sp. nov. abundance increased with increasing temperature and vent emissions. Carbon isotopic ratios suggest that this species could consume both thiotroph and methanotrophic producers. Furthermore sulfur-oxidizing bacteria related to Epsilonproteobacteria and Gammaproteobacteria were detected in the cuticle, in the digestive cavity and in the intestine of O. dyvae sp. nov. suggesting a potential symbiotic association.ConclusionsThis study improves our understanding of vent biology and ecology, revealing a new nematode species able to adapt and be very abundant in active vent areas due to their association with chemosynthetic micro-organisms. Faced by the rapid increase of anthropogenic pressure to access mineral resources in the deep sea, hydrothermal vents are particularly susceptible to be impacted by exploitation of seafloor massive sulfide deposits. It is necessary to document and understand vent species able to flourish in these peculiar ecosystems.
Highlights
Nematodes are an important component of deep-sea hydrothermal vent communities, but only few nematode species are able to cope to the harsh conditions of the most active vent sites
This study improves our understanding of vent biology and ecology, revealing a new nematode species able to adapt and be very abundant in active vent areas due to their association with chemosynthetic micro-organisms
Faced by the rapid increase of anthropogenic pressure to access mineral resources in the deep sea, hydrothermal vents are susceptible to be impacted by exploitation of seafloor massive sulfide deposits
Summary
Nematodes are an important component of deep-sea hydrothermal vent communities, but only few nematode species are able to cope to the harsh conditions of the most active vent sites. Hydrothermal fluids are formed by cold sea water which infiltrates oceanic crust These fluids are heated and enriched with reduced chemicals sorting at very high temperatures (> 400 °C, [1]). Vent ecosystems are formed by organisms able to cope with these extreme conditions (high concentrations of reduced compounds, heavy metals and radionuclides, low oxygen level, and elevated temperatures [2, 3]). The severity of this environment, vents are richer (in term of biomass and productivity) than the adjacent deep-seafloor [4] This elevated macromegafaunal density results from the obligate exploitation of a localized food source that is produced primarily by microbial chemolithoautotrophy, which in turn is directly dependent on reducing substances from vent fluids [5, 6]. Hydrothermal vent fauna interacts directly with microorganisms either through symbiosis, which provides nutrition for the most dominant large invertebrate species (e.g., siboglinid tube worms, bathymodiolin mussels, vesicomyid clams, shrimps [7]), through direct grazing on the microbial communities [6], or, in the case of species like the crab Xenograpsus testudinatus [8], indirectly, as they feed on microbial grazers
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