The proliferating Gastropoda Crepidula fornicata may stimulate macrozoobenthic diversity

Since the late 19th century, the accidentally introduced Gastropoda Crepidu la fornicata has been invading sheltered coastal waters of western Europe. The consequences of this proliferation on macrozoobenthic communities were studied in the Bay of Marennes-Oleron, France. Crepidula fornicata was foun d in a wide range of sediment grain sizes and depths, with however, a predi lection for shallow muddy areas where abundance and biomass reached 4-770 i nd m(-2) and 354 g DW m(-2), respectively. Soft-sediment macrofaunal assemb lages were compared in similar habitats, in the presence and absence of C. fornicata. In muddy and medium sand areas, abundance, biomass and species r ichness of macrofauna were generally greater in presence of C. fornicata, w ith Annelida dominating, although the differences were significant (P<0.05) only in one location out of five. The species composition was moderately d ifferent in the presence of C. fornicata. In coarse sand, the abundance of C. fornicata was low and did not affect abundance, biomass and species rich ness of the macrofauna. However, species composition differed where C. forn icata was absent, with a higher proportion of mobile Crustaceana. The effec t of C. fornicata on benthic communities differs in relation to the habitat they colonize: in muddy sediments, the presence of C. fornicata apparently stimulates zoobenthic community diversity and abundance (mostly deposit-fe eders), whereas in coarser sediments, macrofauna community is different (mo re suspension-feeders) from the community associated with C. fornicata.