Comparison of the life cycle and population dynamics of two Corbicula species, C. fluminea and C. fluminalis (Bivalvia: Corbiculidae) in two French canals

Abstract

Two Corbicula species (C. fluminea and C. fluminalis) were sampled every month in two canals in central France from December 2001 to May 2003. The C. fluminea populations were characterised by (1) a reproduction period that started in March and ended in September-October, during which two peaks of intensity could be distinguished, the first occurring in June and the second in August, the latter corresponding to a density peak, (2) the production of two generations per year, (3) the presence of five cohorts, (4) longevity from 2.5 to 3 years, and (5) a maximum shell length that may exceed 36 mm. In the Loire Lateral Canal, a second period of reproduction was observed during the winters of 2002 and 2003. However, since the number of larvae incubated was always low, we hypothesise that gravid individuals are in fact cryptic hybrids. The C. fluminalis populations were characterised by (1) two reproduction periods, the first occurring in winter during which the number of larvae incubated was low, while the second extended from March to October, reaching its maximum intensity in June and July though the corresponding peak of density did not occur until December, (2) the presence of four cohorts, (3) longevity of four years, a maximum length of 24 mm, a slower growth than that of C. fluminea, and (4) higher sensitivity to freezing. Sudden falls in chlorophyll-a concentrations may play a role in triggering the incubation and spawning periods of this species.