The ichthyoplankton assemblage of the Canaries–African Coastal Transition Zone: A review

In this paper we review information on the ichthyoplankton assemblage of the Canaries–African Coastal Transition Zone (C–ACTZ). This CTZ shows the singularity that the Canary Archipelago interrupts the main flow of the Canary Current and Trade Winds, introducing large mesoscale variability, in the form of island warm wakes and cyclonic and anticyclonic eddies downstream of the islands. Besides, upwelling filaments stretch towards the archipelago from the African coastal upwelling, transporting phytoplankton, zooplankton and fish larvae. They also interact with eddies shed from the islands to exchange water properties and biogenic material. All these mesoscale features influence the composition, structure, abundance and distribution of the larval fish community (LFC) of the region. The Canary Current (CC) and eddies shed from the islands drag larvae of island neritic fish species into the oceanic region and contribute, along warm wakes, to the horizontal distribution of fish larvae. Upwelling and upwelling filaments transport larvae of African neritic species into the oceanic region. These larvae dominate the LFC and account for the relatively high average larval fish abundance found in the C–ACTZ during the summer upwelling season. Filaments originated in the region of Cape Juby–Cape Bojador are entrained around a quasi-permanent cyclonic eddy, trapped between Gran Canaria Island and the African coast, forming a system through which most of the African neritic larvae may return to the African shelf. However, some larvae reach the eastern islands of the Canary archipelago and they may be spread all over the neritic region of the archipelago by eddies shed from the islands. Also in summer, the distribution of the LFC of the C–ACTZ is vertically stratified and fish larvae seem to carry out little or not diel vertical migration. Overall, this study highlights the strong relationship between mesoscale oceanographic processes and the LFC in the C–ACTZ.