Sessile animals that live on the foreshore undergo tidal cycles, and have to face
variations in physical and chemical parameters such as oxygen concentration. During
emersion, availability of dissolved oxygen can be lowered for bivalves, which have only a
small reserve of seawater inside their closed shell. Differences in oxygen concentration
are thus expected to lead to modifications of the metabolism, including changes in
mitochondrial activity. Previous studies investigated air exposure under extreme
conditions, which do not always reflect environmental conditions these invertebrates have
to cope with. In this study, oxidative capacities of gill mitochondria of the oyster
Crassostrea gigas were studied during a tidal cycle period, by
comparing oysters collected after emersion and immersion. Only minor differences were
found in state 3 (oxidative phosphorylation) or state 4 (non-phosphorylating oxygen
consumption) rates between the two conditions. Similarly, no difference was observed in
cytochrome c oxidase activity or in oxygen consumption related to maximal
electron flux through complexes I-IV, II-IV and IV. While capacities of substrate
oxidation were maintained in both emersion and immersion conditions, capacity of
mitochondria to produce adenosine triphosphate (ATP) was significantly lower in oysters
sampled during emersion. These results suggest that although C. gigas
could maintain aerobic metabolism during emersion period within a tidal cycle in
its environment, energy producing mechanisms are affected.