ИСТИНА

Within the framework of the EC FP6 HERMES project, samples were taken at ca. 700 and 1000 m depth in the Gollum Channel System and the edge of the Whittard Canyon during the RV Belgica 2006/13 cruise. These two areas are expected to receive high input of organic matter and phytodetritus, but are typified by different trophic and hydrodynamic conditions. Selected biogeochemical variables of the sediments were analysed in conjunction with structural and functional diversity of nematodes, the numerically dominant group within the meiofauna. The Gollum channels and Whittard Canyon edge were characterised by relatively high meiofauna abundance (1054 – 1426 ind. 10 cm-2) and very high nematode genus diversity (total of 181 genera). The nematode community contrasted between the two study areas, between water depths and between individual sampling stations. In addition, nematode biomass varied between areas and stations and reflected differences in trophic structure induced by local trophic conditions. Sediment layer differences had the largest impact on nematode community structure, indicating that local vertical sediment gradients were more important than other spatial contrasts. For the first time, the “chemosynthetic” genus Parastomonema has been found in deep-sea sediments. This genus is characterised by a degenerated alimentary canal, the lack of a mouth, buccal cavity and pharynx and possess a rudimentary gut containing micro-organisms which have been recognised as sulphur-oxidising bacteria providing their nematode hosts with nutrition. Together with the presence of a new nematode species associated with ectosymbiotic bacteria this may indicate the presence of a reduced environment in these canyon systems.