Relationship between valve activity, microalgae concentration in the water and toxin accumulation in the digestive gland of the Pacific oyster Crassostrea gigas exposed to Alexandrium minutum.
Résumé
The complexity of the relationships between Alexandrium minutum (A.m.) concentration in the water ([A.m.]w), Paralytic Shellfish Poisoning contamination in the digestive gland ([PSP]dg) and valve behavior was explored in oysters Crassostrea gigas. Two experiments were conducted, during which oysters' valve behaviour were analyzed. Oysters, first acclimated for 10-days with the non harmful microalgae Heterocapsa triquetra (H.t.) were exposed to 4 microalgae mixtures at constant total concentrations of 10∙103 cells.ml-1 (experiment-1) and 5∙103 cells.ml-1 (experiment-2): 100% A.m.; 50% A.m.-50% H.t.; 25% A.m.-75% H.t.; 100% H.t. At the end of experiment-2, [PSP]dg were measured. At 10∙103 cells.ml-1, the microalgal ingestion decreased (p < 0.05) with increasing [A.m.]w but not at 5∙103 cells.ml-1 (p > 0.05). The frequency of microclosures specifically increased with [A.m.]w (p < 0.05) and the opening duration with [PSP]dg (p < 0.0001). Oysters exhibiting the maximum increase in opening duration also exhibited the highest [PSP]dg. The results are discussed in terms of oyster physiology and origin of the behavioral response.
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