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Some basic features concerning the subtidal circulation of Patos Lagoon were studied through time series analysis of wind, freshwater discharge, and water level records, as well as by means of experiments carried out with a 3D numerical model. The results indicate that during low to moderate river discharge the wind is the main forcing mechanism in time scales associated with meteorological fronts. The two types of wind action, local and non-local effects, are distinguished and their relative importance is evaluated. Salt water enters the system due to a combination of both remote and local wind effects that favors the development of a pressure gradient towards the lagoon during southwesterly winds. This situation is reversed when northeasterly winds dominate. In the inner parts of the lagoon, local wind plays the major role by inducing set up/set down oscillations. An upwind return flow is then developed under these conditions. During high flood periods, normally observed in late winter, the circulation is driven by freshwater discharge.

In the English Channel, the polychaete Pectinaria koreni forms isolated populations confined in bays and estuaries. To determine the influence of larval dispersal variability on the observed stock fluctuations of the three major Pectinaria koreni populations reported along the French coasts of the eastern Channel, larval dispersal was simulated using a 2D hydrodynamical lagrangian model integrating both the tidal residual and the wind-driven circulation. Year-to-year fluctuations of adult stocks were established from benthic surveys carried out between 1973 and 1998. Larval dispersal patterns vary between populations according to the relative importance of tidal advection and eddy diffusion so that local larval retention is maximal where tidal advection is weak. Wind forcing increases the role of advection on larval transport and modifies greatly the level of retention. Otherwise, wind-induced currents may generate larval colonisation from one population to another one and be involved in reestablishment of depleted populations. Thus, the different local populations of Pectinaria koreni seem to constitute a unique metapopulation, namely a number of subpopulations of adults distributed in a patchy habitat and linked together by their planktonic larval phase. Even if temporal variations of climatic conditions alter larval retention from year to year, larval retention at each site remains generally more intense than larval immigration so that each population can be self-sustained. Year-to-year fluctuations of adult stocks do not seem to be related to larval supply but controlled by post-settlement processes. © 2000 Ifremer/CNRS/IRD/É ditions scientifiques et médicales Elsevier SAS larval dispersal / recruitment / modelling / metapopulation / Pectinaria koreni Résumé -Influence de la variabilité de la dispersion larvaire sur la dynamique d'une métapopulation marine en Manche. En Manche, l'annélide polychète Pectinaria koreni est une espèce inféodée aux sédiments fins sablo-vaseux ce qui lui confère une distribution insulaire, confinée aux baies et aux estuaires. La présente étude a pour objectif de déterminer l'influence de la variabilité du transport des larves sur la variabilité spatiale et temporelle des trois principales populations adultes de pectinaires réparties le long des cô tes françaises de la Manche orientale. La dispersion larvaire a été simulée à l'aide d'un modèle hydrodynamique lagrangien 2D de circulation des eaux de la Manche intégrant la circulation résiduelle de marée et la circulation induite par le vent. * Correspondence and reprints: celine.ellien@snv.jussieu.fr 423 © 2000 Ifremer/CNRS/IRD/É ditions scientifiques et mé dicales Elsevier SAS PII: S 0 3 9 9 -1 7 8 4 ( 0 0 ) 0 0 1 3 6 -5/FLALes fluctuations inter-annuelles des stocks adultes ont été établies à partir de différentes campagnes de prélèvements benthiques effectuées entre 1973 et 1998. Les schémas de dispersion larvaire varient entre les populations en fonction de l'importance relative du courant résiduel de marée et de la diffusion tur...

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