Larval dispersal in the Gulf of Cadiz - Mediterranean Sea system: the case of the Sergia robusta shrimp

The connectivity between the Gulf of Cadiz (northeastern Atlantic) and the Mediterranean Sea has been regarded as an interesting oceanographic and ecological issue, especially considering the missing knowledge on the processes at play in the Strait of Gibraltar. Moreover, the spatial and vertical dispersal of organisms in this highly dynamic system are poorly addressed, particularly for invertebrate larvae. Data on decapod larvae and ocean water masses were collected in three summer surveys along the Gulf of Cadiz and western Mediterranean Sea and were analysed to improve the knowledge about dispersal mechanisms and ecological connectivity in the area. Data revealed different spatial distributions for larvae of Sergia robusta, a common mesopelagic shrimp occurring in both basins. We suggest the reduced shelf width in the northern Alboran Sea coast as one of the promoters of the observed spatial distributions, as it accounts for the strong influence of offshore currents in the innershelf, resulting in a higher concentration of pelagic species. In the northern Gulf of Cadiz, the wider shelf and the complex hydrodynamic processes induce high water mixture, enhancing the along and cross-shore transport, and the occurrence of pelagic species in offshore areas. We hypothesized that the hydrological and hydrodynamic characteristics of each basin were the driven factors of the different distributions. However, factors as the origin of larvae, larval duration and migration behaviour seem to control the larval dispersal range that larvae can withstand to adequately settle and recruit to the adult populations.