The fine sand Abra alba community of the Bay of Morlaix twenty years after the Amoco Cadiz oil spill

The fine sand Abra alba community from the Bay of Morlaix (western English Channel) was strongly affected by the Amoco Cadiz oil spill of April 1978. The long term changes in the community (1977-1996) show that reconstitution of this community is slow (over 10 yr). A progressive recolonization by amphipod Ampelisca populations constituting the dominant species is observed. The results show that it is necessary to survey the affected communities for a long period of time (> 10 yr) after an event to identify the real ecological impact of an oil spill. The abiotic and biotic factor existing in the Bay of Morlaix are favorable to the establishment and the persistence of stable dominant Ampelisca populations in time. The 'climax' concept seems to be applicable to this type of stable environment. The soft-bottom Abra alba community of the Bay of Morlaix may only support a maximal carrying capacity of approximately 10-11 g m-2 (mean annual biomass in decalcified dry weight). The deficit of production during 11 annual cycles may have affected the fish biomass feeding on this community. (author)