Influence du cycle semi-dirune et vives-eaux mortes-eaux sur la disponibilité du matériel particulaire et son utilisation par une population de Mytilus edulis

During a fortnightly tidal cycle, a Mytilus edulis population was submitted to natural food conditions in the bay of Marennes-Oléron. During 4 tidal cycles, in vivo continuous measurements of turbidity and fluorescence were recorded to study the evolution of Total Particulate Matter (TPM), phaeopigments and chlorophyll-a concentrations. Turbidity in the water column is clearly influenced by resuspension of sediment. Degradated cells of phytoplankton were associated with sediments, involving strong correlation between phaeopigments and turbidity. High values of chlorophyll-a were encountered during neap tides when turbidity was low. No relation with resuspension processes were observed. No effect of fortnightly variability on retention was observed by using covariance analysis. No influence of TPM was detected on clearance rate (1.5 1.h(-l).g(-l). Non selectivity of mussels on particles above 2µlm, resulted in equal clearance rates on TPM, phaeopigments and chlorophyll. Relative importance of microphytobenthos and phytoplankton on filtration is discussed.