Modelling the transport and dispersion of Carcinus maenas (L.) larvae over the continental shelf/slope off Northern Portugal in May 2002.

Martinho Almeida, Jesús Dubert, Álvaro Peliz, and Henrique Queiroga
CESAM, Universidad de Aveiro, Aveiro, Portugal

ROMS model is used to study the mechanism of dispersion of green crab larvae, Carcinus maenas (L.), in the shelf of the Western Iberian Peninsula, in the neighbourhood of several estuarine systems (Figueira da Foz, Ria de Aveiro, and Douro River at Porto).

From the point of view of biology, the newly hatched larvae of C. maenas migrate vertically in synchrony with the tidal cycle, in order to be exported out of the estuaries to the shelf. In the shelf, the larvae develops in four zoeal stages and one megalopa in a period of about 1 month. After this time the megalopa stage reinvades the estuary, and the recruitment maxima occurs during spring.

From the point of view of physics, once the larvae are exported to the shelf, they are dispersed by the system of shelf currents. In this presentation we examine the mechanims of dispersion on the shelf, for the period of May-June 2002. ROMS 2.1, including realistic wind forcing, tides, heat fluxes, and stratification was set-up to study the circulation during that period. Lagrangian numerical drifters are released in the neighbourhood of the three estuarine systems, and their temporal evolution is analysed for two cases, with and without diel vertical migration (which has been introduced in the model). The main factor inducing dispersion is the wind forcing, but other factors, like the interaction of vertical migration with tides, are non-negligible.