Oyster's anatomy

The mantle: This thin layer of flesh constitutes the outermost part of the oyster's soft body and facilitates the growth and development of the oyster's shell. It also contributes to the production of nacre that covers its interior.

The hinge: It controls the oyster's opening, while the adductor muscle keeps it closed. This muscle needs to be cut when opening the shell.

The gills: Play a distinct role in ensuring respiration and carrying nutrients to the oyster's mouth. The cilia on the gill axes create a water current that assists in transporting particles the oyster feeds on. Plankton (both phytoplankton and zooplankton), small organisms carried by currents, serve as the oyster's food.

The hepatopancreas: This digestive organ of the oyster serves both as a pancreas and a liver. It synthesizes digestive enzymes and handles the assimilation and storage of nutrients.

The oyster, however, lacks a head: it does not possess a central nervous system.

The food absorbed by the oyster (phytoplankton) can have an impact on the color of its soft body. Thus, the presence of certain microalgae can influence the color evolution of the gills, labial palps, or even the edge of the mantle. This is notably the case with the blue navicula (Haslea ostrearia) found in the 'claires' of Marennes-Oléron, which gives the characteristic green color to the " Fines de Claires Vertes " of this Protected Geographical Indication (PGI).

The oyster is a successive hermaphrodite, meaning it alternates between male and female during its growth. Studies have shown that a two-year-old oyster can change sex multiple times during a single summer. This phenomenon is explained by the water's salinity, a constantly changing characteristic in this unique environment subject to the fluctuating tides and river influences.

Water temperature triggers the preparation and reproductive process of the oyster. As soon as the water temperature exceeds 10°C (usually starting in spring), the oyster produces its gametes, which it releases when the water temperature reaches approximately 18°C. The union of male and female gametes produces a microscopic larva that then drifts with the currents.