The influence of variability in larval dispersal on the dynamics of a marine metapopulation in the eastern Channel

In the English Channel, the polychaete Pectinaria in 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. Willd 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. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.