A modelling study of the respective role of hydrodynamic processes and larval mortality on larval dispersal and recruitment of benthic invertebrates:: example of Pectinaria koreni (Annelida: Polychaeta) in the Bay of Seine (English Channel)

The dispersal of Pectinaria koreni larvae released from the eastern Bay of Seine (English Channel) was studied using a two-dimensional hydrodynamic model which integrates tides, wind-driven currents and eddy diffusion, in order to examine the influence of environmental forcing and mortality on larval population dynamics. A broad agreement between predicted larval dispersal for two spawning events observed in 1987 and field data suggests that numerical modelling may be useful to analyse processes involved in the transport and the dynamics of larval populations. Larval mortality may be as important as hydrodynamic processes on larval losses for the adult population. Tides and eddy diffusion had some effects on larval dispersal, but wind forcing and the timing of spawning in relation to the meteorological environment are predicted to be the main source of variability in larval dispersal rates. Although wind-induced larval transport may produce interannual variations in larval retention and recruitment, predicted retention rates were always sufficient to ensure the maintenance of the adult population, regardless of hydrodynamic conditions. The long-range transport of larvae from the eastern Bay of Seine to distant populations was conditioned by constant strong winds, lasting 15 consecutive days, and should be considered an extremely rare event.