In situ distribution and characterization of the organic content of the oyster shell Crassostrea gigas (Mollusca, Bivalvia)

► Cultivation of commercial oysters is facing the influence of global change in sea water composition. ► Oyster shell layers are calcitic, with different microstructures. ► These layers are irregular and imbricated so that only in situ analyses are possible. ► In situ microscopic analyses show that the irregular layers have different organic compositions.