QUANTITATIVE DISTRIBUTION OF BENTHIC MACR OFAUNA OF THE DOVER STRAIT PEBBLE COMMUNITY (EASTERN ENGLISH-CHANNEL, FRANCE)

Because of strong tidal currents, the bottom of the Dover Strait consi sts of coarse sediment which is colonized by a pebble community. A qua ntitative study, based on 0.1 m(2) quadrat samples taken by divers, wa s conducted on this community to establish the richness of benthic mac rofauna (in terms of biomass and diversity) and to provide conclusive data on global community structure (spatial and temporal heterogeneity , trophic structure). Eight samples were taken between June 1992 and J une 1993, eight replicates being taken on each sampling visit. One hun dred and one species were identified, in 10 zoological groups, and a m ean biomass of 281 g.m(-2) (ash free dry weight) was calculated. The S hannon diversity index was low (H' = 1.24) because of the strong domin ance of three species. The echinoderm Ophiothrix fragilis and the two cnidarians Urticina felina and Alcyonium digitatum accounted for at le ast 97 % of the total biomass at all sampling periods. Spatial heterog eneity, studied at the settle of 0.1 m(2) by hierarchical cluster anal ysis based on Sorensen's qualitative similarity index and by Factor Co rrespondence Analysis on biomasses,seemed low and was due to the stron g dispersion of rare species. Hierarchical cluster analysis and FCA, p erformed at the scale of 0.8 m(2) on periods of sampling, showed tempo ral homogeneity. The seasonal influence on biomass did not affect its distribution in species or trophic groups. Suspension-feeders accounte d for 99.8% of total biomass.