Life cycle and population dynamics of Pisidium subtruncatum MALM (Bivalvia: Sphaeriidae) in the Saône, a large lowland river, at Lyon (France): environmental influences
2005
Mouthon, J.
The Pisidium subtruncatum population of the Saône River at Lyon was sampled every month from September 1996 to December 2000. The hfe cycle of this bivalve is characterised by the appearanée of five cohorts that succeeded each other from May to September-October. The longevity of the two first cohorts was only 3 months, whereas the longevity of the three others, which lived though the winter, reached 11months. We generally observed two to three young release periods for each cohort (iteroparity). Pisidium usually produces one or two cohorts per year and lives from one to four years. The temperatures of the Saône are higher than those of the generally lacustrine habitats of populations studied by others, explaining the disagreement between these results and those of other authors. The magnitude and duration of the floods and the periods when they occur play a decisive role in the population dynamics of this bivalve and can, as in 1999, greatly disturb its hfe cycle. The increase of litter size when density is very low suggests that this species possesses compensation mechanisms that permit readjusting population density after a major decrease.
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