Environmental driving forces determining the epipelagic decapod larval community distribution in the Balearic Sea (western Mediterranean)

The decapod larvae community inhabiting the Balearic Sea surface waters was studied from plankton surveys carried out in the spring and summer of 2004 and 2005 between 38°N 0.5°E and 42°N 6°E. A total of 84 taxa were identified, from seven taxonomic orders. The mean larval densities varied from 0.01-240 (±11.69) individuals 100 m−3in 2004 to 0.40-600 (±26.89) individuals 100 m−3in 2005. The analysis of larval spatial patterns in relation to the observed inter-annual environmental variability indicated that they were associated with the different hydrodynamic conditions. In 2004, mesoscale gyres, both anticyclonic and cyclonic, influenced the surface larval distribution by trapping and retaining larvae near the islands, and these larvae constituted an identifiable community different from a second one occupying the oceanic area, characterized by the presence of mesopelagic species larvae. In 2005, most of the area was occupied by resident surface Atlantic waters, which hindered the northern progression of fresher recent Atlantic waters. This environmental homogeneity resulted in a less contrasting scenario, and a unique community including larvae both of neritic and oceanic decapod species was found in most stations. The contrasting hydrographical situations studied in these years allowed to detect shift boundaries in the larval distribution of neritic species, indicating that the hydrographically more homogeneous years may lead to a higher dispersion of neritic decapod larvae.