First considered as simple components of an impermeable barrier, it has been shown that membrane lipids would have a more important biological role. These lipids could modify the environment of membrane enzymes and modulate their activity. In this thesis, these relationships have been studied in mitochondria of the oyster Crassostrea gigas. Bivalves undergo major environmental changes and adaptation to these changes may require a membrane remodelling, which makes these animals interesting models to study the relationship between membrane structure and membrane processes. In this study oysters were fed in hatchery with two monospecific algal diets, T-Iso and Chaetoceros gracilis, and an equilibrated mix of both algae. Despite significant changes in fatty acid composition induced by these diets, mitochondrial capacities remained stable. On the other hand, the comparison between hatchery-reared oysters and oysters reared in their natural environment revealed significant changes in mitochondrial capacity, which could be related to modulation of phospholipid class composition and unsaturation. These differences can not be explained by the influence of tidal cycles. Indeed, despite a change in ATP production, mitochondrial activity was shown to be similar in oysters collected during emersion and immersion.Mitochondrial homeostasis observed in this study could be a way for oysters to cope with biotic (food availability) and abiotic (oxygen availability) variations in the natural environment of C. gigas, and to maintain their physiological functions despite these variations.
