Restructuring of the 'Macaronesia' biogeographic unit: A marine multi-taxon biogeographical approach

Abstract

The Azores, Madeira, Selvagens, Canary Islands and Cabo Verde are commonly united under the term "Macaronesia". This study investigates the coherency and validity of Macaronesia as a biogeographic unit using six marine groups with very different dispersal abilities: coastal fishes, echinoderms, gastropod molluscs, brachyuran decapod crustaceans, polychaete annelids, and macroalgae. We found no support for the current concept of Macaronesia as a coherent marine biogeographic unit. All marine groups studied suggest the exclusion of Cabo Verde from the remaining Macaronesian archipelagos and thus, Cabo Verde should be given the status of a biogeographic subprovince within the West African Transition province. We propose to redefine the Lusitanian biogeographical province, in which we include four ecoregions: the South European Atlantic Shelf, the Saharan Upwelling, the Azores, and a new ecoregion herein named Webbnesia, which comprises the archipelagos of Madeira, Selvagens and the Canary Islands.

Figure 1

Geographical areas used for the construction of the checklists (cf. Supplementary Material, Tables S1 to S5) and for the biogeographical analysis. AST – Asturias (north Spain); AZO – Azores Archipelago; BIS – Bay of Biscay sensu lato, from English Channel to Punta Estaca de Bares, Galicia, Spain; CAB – Cabo Verde Archipelago; CAD – Gulf of Cádiz; BRI – British Isles; CAN – Canary Archipelago; IBE – Iberian shores (from southern Bay of Biscay to Portugal and Gulf of Cádiz); MAD – Madeira Archipelago; MED – western Mediterranean Sea; NWA – northwest African shores (Atlantic Morocco, from Straits of Gibraltar south, Western Sahara to Cape Blanc (Mauritania); POR – Portugal [western Atlantic Iberian façade (from Cabo Vilán, western Galician shores, down to Cape São Vicente) and southern shores of Algarve]; SEL – Selvagens Islands; SEN – Senegal; STP – São Tomé and Príncipe Archipelago; TWAF – Tropical West Africa [from Cape Blanc (Mauritania) south to Cape Frio (Angola)].

Figure 2

Fish families with highest richness of single archipelagic endemic species in Macaronesia. AZO – Azores; MAD – Madeira; SEL – Selvagens; CAN – Canary Islands; CAB – Cabo Verde.

Figure 3

Mollusc gastropod genera with highest richness of single archipelagic endemic species in Macaronesia. AZO – Azores; MAD – Madeira; SEL – Selvagens; CAN – Canary Islands; CAB – Cabo Verde.

Figure 4

Dendrograms depicting the biogeographic similarity between areas. Numbers correspond to the bootstrap values providing support for each tree node (100 repetitions of 100 trees). Coastal fishes (Simpson index/UPGMA; cophenetic correlation = 0.847), Echinodermata (Jaccard index/UPGMA; cophenetic correlation = 0.833), Gastropoda (Simpson index/UPGMA; cophenetic correlation = 0.936), Crustacea Brachyura (Jaccard index/UPGMA; cophenetic correlation = 0.915), macroalgae (Jaccard index/UPGMA; cophenetic correlation = 0.883), Polychaeta (Jaccard index/UPGMA; cophenetic correlation = 0.952). Mollusc gastropods and macroalgae from 0–50 m depth; coastal fishes, echinoderms, brachyuran crabs and polychaetes from 0–200 m. For acronyms of each geographical area, see legend of Fig. 1. Letters A, B, (…), Y, represent the optimal number of clusters which were validated by Mantel statistics (Pearson).

Figure 5

Dendrogram depicting the biogeographic similarity between areas for the shared endemic species (Jaccard index/UPGMA; cophenetic correlation = 0,935). Numbers correspond to the bootstrap values providing support for each tree node (100 repetitions of 100 trees). Letters A, B, C, represent the optimal number of clusters which were validated by Mantel statistics (Pearson).

Figure 6

Scheme illustrating the circulation pattern of the main surface currents in the North and Central Atlantic Ocean. GS – Gulf Stream; NAC – North Atlantic Current; AC – Azores Current; SWEC – Southwest European Current; MADC – Madeira Current; CANC – Canary Current; NEC – North Equatorial Current; NECC – North Equatorial Counter Current; MC – Mauritania Current; GC – Guinea Current.

Figure 7

Biogeographical classification of the Macaronesian archipelagos. The Lusitania Province includes the Azores ecoregion, the Webbnesia ecoregion (which integrates the archipelagos of Madeira, Selvagens and Canary Islands), the South European Atlantic Shelf ecoregion and the Saharan Upwelling ecoregion. The West African Transition Province includes the Cabo Verde subprovince and the Sahelian Upwelling ecoregion. For acronyms of each geographical area, see legend of Fig. 1.