DISPERSAL OF ECHINODERM LARVAE IN A GEOGRAPHICAL AREA MARKED BY UPWELLING (LIGURIAN SEA, NW MEDITERRANEAN)

A spatio-temporal survey of some echinoderm larvae was conducted along a transect of 28 nautical miles from the Bay of Villefranche, France, halfway to Corsica. Distribution patterns and mechanisms responsible for larval dispersal, viz. water currents, hydroclimate and vertical movements, were studied. The echinoderm larvae exhibited weak vertical migration (a few meters), remaining in the surface layer. They are therefore subjected to hydrodynamic constraints which either limit or promote dispersal away from the nursery beds. Larval concentration decreased with distance from the coast and was generally restricted to within 16 miles of the coast. This distance coincided with the location of a coastal divergence zone where rising subsurface waters confined larvae to the Ligurian Current.