Cytological and biochemical changes in the digestive gland of Pecten maximus throughout a one-year period were investigated in the Bay of Brest (France) relative to lipid storage and glycogen and α-amylase concentrations in tubuloacinar terminations. Seasonal variations in both cell structure and biochemical composition were observed. These changes were independent of the tidal cycle, but correspond to phytoplankton abundance. From November to January, cells of digestive acini were hypertrophied due to the high lipid storage. From February to May, these reserves were markedly reduced, cell size decreased, and the acinar lumen was clearly apparent. From May to September, the RNAs transcribing for α-amylase increased, and a correlation was found between digestion events and lipid storage in acinar cells. The relationships between metabolite transfers from digestive gland to gonad and other tissues are described. Distinct lipid storage sites appear to be associated with maintenance energy and acute demand energy, such as gametogenesis when adductor muscle reserves have been depleted. The digestive gland may thus function as a relay organ during periods of energetic stress, notably during the first gametogenesis in February and March and for shell growth in early spring.