Laboratoire d’Océanographie Physique et Biogéochimique

“The influence of hydrodynamic processes on zooplankton transport and distributions in the North Western Mediterranean Sea : estimates from a Lagrangian model”

     A Lagrangian module has been developed to simulate the transport and distributions of zooplankton individuals coupling with the 3D circulation model SYMPHONIE. The influence of hydrodynamic processes on zooplankton transport and distributions in the North Western Mediterranean Sea (NWMS) has been investigated from March to August 2001. The individuals are either considered as passive particles or able to realize diel vertical migrations (DVM) with a simple swimming pattern. The individuals are released every 3 days from two areas : the surrounding of the DYFAMED sampling station in the central Ligurian sea and the plume of the Rhone river. The individuals are tracked during 40 days. Results suggest strong seasonal patterns appear in the distributions of the individuals released at DYFAMED sampling station. Individuals could be spread all over the NWMS basin after 40 days but different patterns occurs following the season, the depth of release of the individuals, and the capacity of DVM or not. An offshoreshelf transport only occur in April and May with particles ending in the Gulf of Lions (GoL) in low concentrations. For the other months, the north current can be properly considered as a barrier for particles entering into the GoL from the offshore sea. At the end of the 40 days, passive individuals released in the plume of the Rhone River are spread on the GoL shelf or in the Catalan sea. Following the season between a quarter to an half of the initial released individuals stay in the Gulf. Simple DVM behavior does not increase the retention on the shelf.