Large-scale Shoreline Configuration Influences Phytoplankton Concentration and Mussel Growth

The main environmental abiotic and biotic factors and the feeding activity of adult anchovy were analysed in the Bay of Biscay during the spawning period (spring) in neritic and oceanic areas characterized by high anchovy densities. In the neritic area located in the water plume of the Gironde estuary (` GIR ʹ) chlorophyll concentrations and zooplankton biomass, above and below the thermocline, were higher than in the oceanic area (` FAC ʹ). Copepods constituted the dominant group of zooplankton (>85%); the main species were, decreasingly: Clausocalanus sp.- Paracalanus parvus, Oncea sp., Corycaeus sp., Temora longicornis and Oithona sp. in GIR and Clausocalanus sp.- P. parvus, Oithona sp.,Centropages chierchiae and Acartia clausi in FAC area. Anchovy feeding activity mainly occurred during the day and was higher in the FAC area than in the GIR area. Food ingested constituted exclusively of zooplankton, in particular copepods that made up about 98%;T. longicornis, Oncea sp. and Corycaeus sp. were the main species in the ` GIR ʹ area and C. chierchiae in the FAC area. Considering anchovy distribution and feeding characteristics, (fullness index, preponderance index especially) the results showed that, in both areas, biting (anchovy taking of prey) is the dominant or exclusive pattern of anchovy feeding behaviour. Feeding efficiency appears to be most related to zooplankton specific composition than to zooplankton abundance.