Role of biotic interactions on seasonal migrations of the macrozoobenthos living in the upper tidal-flat of the Mont-Saint-Michel bay, France

Abstract

On the tidal flat of the western part of the Mont-Saint-Michel bay, the macrozoobenthos of the upper flat is characterised by an assemblage of the Macoma balthica community. The dominant species are M. balthica, Nereis diversicolor and Corophium volutator. A field monitoring during a 1-year period along a four-stations transect perpendicularly to the shore showed that biotic interactions affected the local distributions of these species. This was particularly obvious from late spring to late summer while, because of the density increases, competitions for space and/or resources were induced, which stimulated migrations. Intra-specific competition seemed to induce the migration of the 1-year-old M. balthica. Consequently, the migration of the young bivalves from the level where this species is dominant to upper levels stimulated the migration of C. volutator population. This migration had a negative effect on the abundance of the amphipods. The migration of N. diversicolor during the end of the summer population to the lower levels of the tidal flat seemed to prevent the return of the C. volutator population to their original before-migration area, even though M. balthica density decreased.