Long-term changes in muddy fine sand community of the Rance Basin: role ofrecruitment

Dynamics of the Abra alba muddy fine sand community of the Rance Basin (wes tern English Channel), initially sampled in one station by Retiere at the b eginning of the 1970s after the tidal power station built at the mouth of t he estuary went into service, was reassessed from 1995 to 1997. Results sho wed a more 'mature' community in 1995-1997 with an increase in the number o f species. After a short period, in spring 1995, during which the structure of the community was comparable to those described in 1972-1973, the assem blage was characterized by a great interannual structural stability. Densit ies of dominant species seem to fluctuate around a mean value comparable to the carrying capacity of the biota for these species. The recruitment of t he dominant species with a long life span appears low compared to the densi ties of adults but seems sufficient to assure the replacement of individual s. Our results suggest that the pattern of massive recruitment followed by high mortality rates could not be the general rule and that a pattern of mo derate recruitment followed by low post-settlement mortality of recruits sh ould be more frequent.