SEASONAL-VARIATIONS IN FAUNAL DISTRIBUTION AND ACTIVITY ACROSS THE CONTINENTAL-SLOPE OF THE GOBAN SPUR AREA (NE ATLANTIC)

Density, biomass and community structure of macrofauna were estimated together with several sediment characteristics at seven stations rangi ng from 208 m to 4460 m water depth along the OMEX transect in the Gob an Spur area (NE Atlantic) during three seasons (October 1993, May 199 4, and August 1995), Median grain size decreased with increasing water depth and showed no differences between the seasons. The percentages of organic carbon and total nitrogen were highest at mid-slope depths (similar to 1000 to 1500 m), and were significantly higher in August a t the upper part of the slope to a depth of similar to 1500 m. The C:N ratio in the surface layer amounted to similar to 7 to 8 in May, simi lar to 10 to 12 in August and similar to 14 to 17 in October at all st ations (except the deepest at 4460 m, where it was similar to 11 in Ma y and August), indicating arrival of fresh phytodetritus in May, and t herefore seasonality in food input to the benthos. Densities of macrof auna decreased exponentially with increasing water depth, Significantl y higher densities of macrofauna were found in May at the upper part o f the slope to a depth of similar to 1500 m. These differences were ma inly due to high numbers of postlarvae of echinoids at the shallowest station and ophiuroids at the deeper stations, Biomass values also dec reased with increasing water depth, but biomass was relatively high at the similar to 1000 m station and low at similar to 1500 m, due to re latively high and low mean weights of the individual macrofaunal speci mens. No significant differences in biomass were found between the sea sons. Respiration was high (15 to 20 mgC . m(-2). d(-1)) in May at the upper part of the slope to a depth of similar to 1000 m and low (1-3 mg C . m(-2). d(-1)) at the deeper part. At the shallowest stations to a depth of similar to 1000 m respiration was highest in May, at the m id-slope stations (similar to 1400-2200 m) it was highest in August, w hereas the deepest stations (similar to 3600 to 4500 m) did not show a ny differences in respiration rates. In conclusion: seasonal variation in organic input is reflected in density, community structure and act ivity of the macrofauna along the continental slope in the NE Atlantic .