EFFECT OF THE PSP-CAUSING DINOFLAGELLATE, ALEXANDRIUM SP. ON THE INITIAL FEEDING RESPONSE OF CRASSOSTREA-GIGAS

The effects of toxic and non-toxic strains of Alexandrium sp. on the i nitial feeding responses of the Pacific oyster Crassostrea gigas were determined by continuous monitoring of the clearance rate of individua l oysters. This was determined fluorometrically by loss of fluorescenc e of live microalgae introduced as food. Feeding oysters with toxic or non-toxic A. tamarense and toxic A. fundyense resulted in stop/start clearance behaviour. In contrast, control oysters fed a reference micr oalga, Isochrysis sp., known to support their growth, did not exhibit this behavior. Pacific oysters acclimated to Isochrysis sp., fed mixtu res of Alexandrium/Isochrysis, showed further evidence of stop/start c learance. Exposure for periods up to 48 hours with non-toxic A. tamare nse did not enhance clearance of either Alexandrium or Isochrysis. (C) Ifremer-Elsevier, Paris.