Ecology of plaice (Pleuronectes platessa) in fish assemblages of beaches of the Opale Coast (North of France) during spring 1997

In recent years, many studies on the ecology of demersal populations nurser ies have focussed on subtidal areas and estuaries, whereas the intertidal z one, especially sandy beaches, have been more or less neglected. Weekly sam pling was carried out over 7 weeks in spring 1997, at three intertidal beac hes (Merlimont. Wissant and Oye-plage) along the Opale Coast. The aim was t o determine whether the intertidal zone is of any ecological importance for flatfish. Sampling was achieved with a standard beam trawl, as the one use d by local fishermen. Each sampled site showed low diversity of the ichthyo fauna and was dominated by the plaice, Pleuronectes platessa and the shrimp , Crangon crangon. Analysis of plaice abundance and size distribution showe d differences among beaches throughout time. To the south, succession of co horts was observed whereas a weekly settlement is suggested for the norther n beaches. The variability of plaice settlement dynamics in those areas mig ht be influenced by temperature and tides as well as by mutual predation be tween young plaice and shrimp, which influence the plaice dynamics. This st udy shows the role of sandy beaches as an ecosystem temporally occupied by young flatfish throughout this period of their life cycle.