Transport pathways of decapod larvae under intense mesoscale activity in the Canary-African coastal transition zone: implications for population connectivity

We investigate the transport dynamics of decapod larvae in the Canary-African coastal transition zone (C-ACTZ), where larval assemblages are poorly known. In August 1999, during the FAX99 cruise, the waters downstream of the Canary Island archipelago displayed intense mesoscale activity, with numerous cyclonic and anticyclonic eddies as well as upwelling filaments. Our results illustrate a close relationship between these mesoscale oceanographic structures and the distribution of decapod larvae, using both field observations and Lagrangian transport modelling. Analysis of plankton samples shows that larvae of pelagic species were excluded from filament waters, whereas larvae of neritic species were heterogeneously distributed, suggesting that the C-ACTZ is a mixing area where larvae originating from both the Canary Islands and the African coast may be present at the same time. This finding was supported by the simulations, which suggested that the larvae collected in the offshore waters south of Gran Canaria came mainly from the African population (between Cape Bojador and Cape Juby) during early August, whereas during the second half of August the targeted area was dominated by larvae released from Fuerteventura populations. Our observations introduce new insights into our understanding of marine population connectivity, the dispersal pathways of the terrestrial biota, and general biogeography in the region.