Long-term changes in sand-bottom macrofauna along the coast of Provence (northwest Mediterranean Sea)

At a time when there is a great deal of talk of the degradation of the coastal environment and of biodiversity being threatened, we felt it would be of interest to sample the macrofauna of five sites at five metres depth in well sorted fine sand at a thirty-year interval (1966-1996), using the same techniques. Four seasonal samplings provided comparative data at each site on the species richness (S), density (N) and biomass (B). The S values are comparable and even on the increase at two stations. Nevertheless, we observed a general tendency towards decline in the relative abundance of the crustacean group. From the quantitative point of view (N and B), the changes observed would appear to result from the impact of clearly identifiable human pressure, such as the diversion of a small coastal river outside the Gulf of Marseilles, or, conversely, the increase of nutrient inputs from the Rhone along the coast of the Camargue. In the latter case, the rate of nutrient inputs was amplified by a climatic factor which contributed to increasing the Rhone's flow rate during the two years preceding the re-sampling of the site in 1996. Apart from these two cases, there would appear to be little significant alteration in the macrofauna, although these fine sand, relatively shallow bottoms are naturally subject to patterns of alternation in the relative dominance of certain zoological groups such as, for example, the prey/predator couple formed by molluscs and echinoderms. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.