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 nurseries have focussed on subtidal areas and estuaries, whereas the intertidal zone, especially sandy beaches, have been more or less neglected. Weekly sampling was carried out over 7 weeks in spring 1997, at three intertidal beaches (Merlimont, Wissant and Oye-plage) along the Opale coast. The aim was to determine whether the intertidal zone is of any ecological importance for flatfish. Sampling was achieved with a standard beam trawl, as the one used by local fishermen. Each sampled site showed low diversity of the ichthyofauna and was dominated by the plaice, Pleuronectes platessa and the shrimp, Crangon crangon. Analysis of plaice abundance and size distribution showed differences among beaches throughout time. To the south, succession of cohorts was observed whereas a weekly settlement is suggested for the northern beaches. The variability of plaice settlement dynamics in those areas might be influenced by temperature and tides as well as by mutual predation between young plaice and shrimp, which influence the plaice dynamics. This study shows the rote of sandy beaches as an ecosystem temporally occupied by young flatfish throughout this period of their life cycle.Original Abstract: Ces dernieres annees, de nombreuses etudes sur les nourriceries des poissons nectobenthiques ont ete concentrees sur les zones subtidales et les estuaires, plutot que sur leur composante intertidale :les plages sableuses. Cette etude porte sur le role ecologique de la zone intertidale pour les poissons plats. L'echantillonnage a ete mene au printemps 1997, durant 7 semaines, sur 3 plages de la Cote d'Opale :Merlimont, Wissant et Oye-plage. II a ete realise a l'aide d'un chalut a perche standardise, couramment utilise par les pecheurs a pied. Chacun des sites a montre une faible diversite de l'ichtyofaune et etait domine par la presence de la plie, Pleuronectes platessa, et de la crevette, Crangon crangon. L'analyse de la densite et des compositions en taille des plies a montre des differences entre les plages sur la periode consideree. Ainsi, au sud de la zone etudiee, plusieurs groupes successifs d'individus ont pu etre mis en evidence. Au nord, sur les deux autres sites, une dynamique de renouvellement permanent des individus a ete observee. Cette etude montre le role de la zone medio-littorale des plages sableuses, comme etant un ecosysteme colonise temporairement par les jeunes plies durant une etape