Decline of Dreissena polymorpha in the River Moselle: biotic and abiotic key factors involved in dynamics of invasive species

Macroinvertebrate communities sampled in 1994, 1995 and 1996 showed that th ree invasive exotic species (Dreissena polymorpha, Corophium curvispinum an d Corbicula fluminalis) were well established and coexisted in the River Mo selle. Results highlighted a decline of the zebra mussel population, the ol dest invader considered, between 1994 and 1996. Benthic densities decreased . The recruitment of juveniles was unsuccessful and population was clearly ageing over the considered period. These results were confirmed by a declin e of the veliger density (reproduction capacity) between 1994 and 1998. Bio tic and abiotic factors which have probably influenced the zebra mussel pop ulation dynamics are discussed. The recent establishment of C. curvispinum in the same mesohabitat type and the massive development of Corbiculidae su ggested a possible competition for habitat and/or food between these invasi ve species. A first abiotic factor was the hydrological regime of 1994 and 1995, which was particularly high for the 1992-1998 period. It may have rem oved the substratum and then favoured the settlement of an opportunistic sp ecies like C. curvispinum with a high reproductive output and a reproductio n period early in the year. A second abiotic factor was the physicochemical water quality of the River Moselle. In 1993 and 1993 the high chlorophyll- a concentration probably favoured the incubation of C. curvispinum, and in 1994 the pH did not reach an optimal value for the survival of D. polymorph a veligers. Our results describe key factors for understanding the populati on dynamics of invasive species in regard to environmental changes and proc esses involved in future ecosystem invasions.