Long-term changes (1979–1990) in three benthic communities (eastern English Channel): Use of factor analysis and rank-frequency diagrams for studying structural developments

Abstract

Long-term variations (1979–1990) of three benthic communities (Eastern Channel, France) were analysed by means of factor correspondence analysis (FCA), a multivariate method of ordination in reduced space, and rank-frequency diagrams (RFD). FCA distinguished periods of relative homogeneity and periods of strong variations in the structure of the communities. Two communities, the pebbles community and a rich and diverse mussel (Mytilus edulis) bed, showed great variations in the abundance of the main species (Ophiothrix fragilis in the first one, andM. edulis in the second one) which generated the enrichment of the community by their suspension-feeding behaviour. Beyond the multi-annual cycle induced by these variations, both communities seemed to be quite stable as no continuing trends could be seen. The third community, established on heterogeneous sand, also showed a multi-annual cycle linked to granulometric variations of the sediment. As passive supplies of detritus were not important and suspension feeders could hardly live in these conditions, the community stayed poor and was dominated by carnivores and deposit-feeders.