Écologie de la reproduction de l’huître creuse, Crassostrea gigas, sur les côtes atlantiques françaises. Vers une explication de la variabilité du captage

Spat collecting supplies numerous oyster-farmers with young cupped oyster, C. gigas. Since the end of the nineties, professionals have noticed an increasing variability of the number of spat among years. This thesis aimed to identify the origin of the variability of oyster recruitment. This question is addressed by different methods for each step of the reproduction of oyster: a DEB model for gametogenesis, valvometry for spawning, cohort analysis for larval stage and hydrodynamic models for dispersion. At the stage of the gametogenesis, variations of fecundity appear to be mainly influenced by phytoplankton quality. The study of spawning shows that it happens during high tides of spring tides, leading to a spawning that is foreseeable. For Arcachon Bay, spat number depends on the survival of larval cohort that is in turn submitted to a complex climatic effect mainly based on sea temperature. Arcachon and Marennes-Oléron Bays seem also to depend on the variability of larval supply: the supply of larvae is provide by a source of larvae in the north of spat collecting areas for Charente and by an local source that seems to decrease for Arcachon. This decrease of larval supply and the climate effect are the two suspected origins of the increased variability of spat collecting in Arcachon Bay.