Impact of oyster culture on nutrients and oxygen fluxes in a coastal lagoon.

The impact of suspended oyster culture (Crassostrea gigas, Thunberg) on oxy gen and nutrient fluxes has been studied in situ, in a coastal lagoon (Thau , France), during a seasonal cycle. On the first plan of the multiple facto rial correspondences analysis (MCA), seasons were well discriminated. The f luxes were maximum in summer and minimum in winter. However, this seasonal pattern was not only linked to the water temperature, as autumn and spring (similar temperatures of about 12 degrees C) were distinct in the second fa ctorial plan (2.3). Oxygen uptake by the oyster cultures varied between 0 m u mol m(-2) h(-1) (January) and 11 823 +/- 377 mu mol m(-2) h(-1) (July). A mmonia and nitrate-nitrites were released into the water column respectivel y at a rate of 2905 +/- 327 mu mol m(-2) h(-1) and 891 +/- 88 mu mol m(-2) h(-1) in the summer and 0 mu mol m(-2) h(-1) and 177 +/- 97 mu mol m(-2) h( -1) in the cold season. During the summer, the nitrate-nitrites flux was ab out 20 % of the total dissolved inorganic nitrogen production. Phosphate re lease was low except for two periods during which an important release was measured; in May (1686 +/- 44 mu mol m(-2) h(-1)) and in November (2691 +/- 800 mu mol m(-2) h(-1)). No linear relation between water temperature and phosphate flux was found. In Than Lagoon, oyster cultures (oysters and epib iota) by producing 2 x 10(7) mol-N y(-1) play a central role in nitrogen re newal in the water column. (C) Elsevier, Paris.