Structural analysis of the meiobenthos communities of the shelf break area in two stations of the Gulf of Biscay (N.E. Atlantic).

In a first attempt to obtain information in order to characterize the shelf break zone, the meiobenthos communities of two fine sandy stations of 190 m and 325 m depth in the Gulf of Biscay off the Spanish coast were investigated in relation to some environmental characteristics (sediment composition, chlorophyll a content, redox values). The nematodes, which are the dominant taxon, were studied in detail. Their communities are relatively poor in densities (840 and 779 individuals per 10 cm2) and biomass (0.137 and 0.334 mg dwt/10 cm2) compared to those of shallow coastal areas. The dominance of small species (mean individual biomass : 0.169 and 0.423 mug dwt) and a low total biomass can be related to the low chlorophyll a content (maximum of 1.14 mug/g). However, the number of nematode genera is much higher (46 and 62 genera per station) than on the continental shelves (often less than 40 species per 10 cm2). Sabatieria, Daptonema, Minolaimus, Richtersia and Halalaimus are the dominant genera in the two stations. These are also characteristic genera for the abyssal zone. The composition of the nematode communities is more similar to deep-sea communities than to those from subtidal zones. The low food supply is considered as an important structuring factor.