Effet des biodépôts de l'huître Crassostrea gigas (Thunberg) sur l'accumulation de matières organiques dans les parcs du bassin de Marennes-Oléron

The accumulation of biodeposits brings about geochemical modifications of the underlying sediment, that are noticeable. The increase can reach 83% of the amount of organic carbon. By catching the deposits on the spot and by gathering them directly from the oyster tables we get a daily deposit that can weigh, according to season, between 8 and 99 g of carbon a square meter. The recycling of important quantities of organic matter increase the oxygen needs and the most reducing environment provides opportunities for ammonification and reduction of sulfate into sulfur. So we can consider that there is as much as 4 times more sulfurous hydrogen in intensive oyster-growing areas. This output of sulfurs seems to cause the oyster filtration some damage (Ito et Imaï, 1955) as well as the survival of oyster larvae (Caldwell, 1975).