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Archive ouverte | Oceanolica Acta (0399-1784) (Gauthier-Villars), 1997 , Vol. 20 , N. 2 , P. 453-460
Edité par Gauthier-Villars
Because of strong tidal currents, the bottom of the Dover Strait consists of coarse sediment which is colonized by a pebble community. A quantitative study, based on 0.1 m(2) quadrat samples taken by divers, was conducted on this community to establish the richness of benthic macrofauna (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 June 1993, eight replicates being taken on each sampling visit. One hundred and one species were identified, in 10 zoological groups, and a mean biomass of 281 g.m(-2) (ash free dry weight) was calculated. The Shannon diversity index was low (H' = 1.24) because of the strong dominance of three species. The echinoderm Ophiothrix fragilis and the two cnidarians Urticina felina and Alcyonium digitatum accounted for at least 97 % of the total biomass at all sampling periods. Spatial heterogeneity, studied at the settle of 0.1 m(2) by hierarchical cluster analysis based on Sorensen's qualitative similarity index and by Factor Correspondence Analysis on biomasses,seemed low and was due to the strong dispersion of rare species. Hierarchical cluster analysis and FCA, performed at the scale of 0.8 m(2) on periods of sampling, showed temporal homogeneity. The seasonal influence on biomass did not affect its distribution in species or trophic groups. Suspension-feeders accounted for 99.8% of total biomass.
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