MEPS 347:233-245 (2007)  -  DOI: https://doi.org/10.3354/meps06981

ABSTRACT: The Princeton Ocean Model coupled with a particle-tracking module is used to assess the effects of physical forcing and vertical migratory behaviour on the transport and dispersion of larvae in the region of freshwater influence (ROFI) of the eastern English Channel (EEC). Results of numerical modelling are compared with the observed concentrations of flounder Pleuronectes flesus larvae. The simulations show that accumulation of neutrally buoyant particles occurs on the ROFI margin, 20 km off the French coast. Tides and freshwater input induce the net along-shore northward transport. Tidal currents modulate the magnitude of horizontal transport, whereas the freshwater input controls the location of accumulation zones. The vertical migration of particles causes a significant departure from the passive transport pattern and modifies the intensity of dispersion. The diurnal (light dependent) migration tends to decrease the magnitude of the cross-shore dispersion of particles. When the vertical migration is controlled by the tidal (sea level variation) cycle, particles move northward faster, and exhibit less dispersion. The migratory behaviour synchronised with the tidal currents (ebb/flood cycle) produces a relatively slow northward migration and a low dispersion in both along- and cross-shore directions. This suggests that vertical migratory behaviour could control the intensity of dispersion and the relative dominance of either retention or downstream advection of the larvae in the EEC.

KEY WORDS: Larval transport · Vertical migration · Particle tracking · Tides · English Channel