Life cycle of Musculium lacustre (Bivalvia: Sphaeriidae) in the Saône river at Lyon (France) : a curious life strategy

Cemagref, 3 bis quai Chauveau, CP 220, 69336 Lyon cedex 09, France.

Corresponding author: jacques.mouthon@Lyon.cemagref.fr

Abstract

The life cycle of Musculium lacustre populations in the Saône river at Lyon was studied over a three-years period. Following the growth period which occurs from March to June, adults released larvae, then disappeared during the summer. Only a few newborn of the new generation that appeared in May and June grow and give birth to a second generation at the end of summer or in autumn. Most of the juveniles of the first generation estivate, then hibernate with those of the second generation until the following spring. The individuals of each generation only reproduce once (semelparity). Longevity of M. lacustre is from 13 to 14 months. In 2001, the spring flood disturbed the progress of the life cycle and delayed the appearance of the new generation for one month. In 2003, a large accumulation of dead leaves at the beginning of winter and high spring temperatures led to considerable production of larvae. However, this was not followed by an increase in numbers: high mortality among the newborn occurred during May and June. These observations suggest that M. lacustre populations of the Saône are habitually food-limited. Nonetheless, the life cycle strategy adopted by this bivalve enabled it to withstand the high summer temperatures of 2003 as opposed to other Sphaeriidae (Pisidium) which disappeared in August.