A MODEL OF LARVAL DISPERSION COUPLING WIND-DRIVEN CURRENTS AND VERTICAL LARVAL BEHAVIOR - APPLICATION TO THE RECRUITMENT OF THE ANNELID OWENIA-FUSIFORMIS IN BANYULS BAY, FRANCE

We present a mathematical model of larval dispersal into a coastal zon e dominated by wind-driven currents: larvae are considered as active p articles tracked by the 3-D (3-dimensional) velocities calculated by a physical model sophisticated enough to give a good representation of the 3-D structure of wind-driven currents. As an application, we model the larval recruitment of the annelid Owenia fusiformis in Banyuls Ba y, France, located at the southwest extremity of the Gulf of Lions. Th e currents are generated by the permanent offshore Liguro-Provencal ci rculation and by time-varying winds, the swimming behaviour of larvae is assumed to be only vertical, the spawning zones are in 2 adjacent b ays and the pelagic phase lasts about 4 wk. Larvae are assumed to be s uccessfully recruited if they settle after pelagic morphological chang es on the substratum suitable to their benthic development. Larvae whi ch do not belong to the successful recruitment either settle too young on the suitable substratum or go out of the suitable substratum. The model shows that the fate of the larvae tracked by the currents appear s to be determined early in the pelagic phase by being trapped in low current zones. Simulations allow the deduction of the advection losses for different winds: the proportion of larvae reaching the adult habi tat is 60 % at maximum for downwelling conditions and 15 % at minimum for initial upwelling conditions. Our results indicate too that under the most frequent wind conditions no mixing occurs between populations of the 2 adult habitat zones which are 1.6 km apart from each other a nd that no successful recruitment occurs from larvae coming from bays located at the north of the considered coastal zone. Only combinations of changing wind conditions could permit arrival of larvae from Pauli lles Bay to Banyuls Bay. The interest of such individual-based models consists not only in increasing our understanding of the link between spatial and temporal dynamics of meroplanktonic populations but also i n allowing us to explore the potential effects of habitat alteration o n those populations.