Palaeobiogeography of NE Atlantic archipelagos during the last Interglacial (MIS 5e): A molluscan approach to the conundrum of Macaronesia as a marine biogeographic unit

In order to understand the complex evolutionary processes and patterns that explain current island biodiversity, large datasets and long-term analysis are required. The Last Interglacial (LIG) was one of the warmest interglacials during the last million years. How species mobility changed during this period in the Macaronesia geographical region has long intrigued scientists. It is well established that the northward range expansion of tropical species occurred in the Macaronesian geographical region, but as a marine biogeographic unit, the term "Macaronesia" has not gained a consensus among the scientific community. For the first time, a thoroughly revised and updated checklist is presented for shallow-water marine molluscs from the Atlantic and Mediterranean during the LIG. Based on these wide ranging data, the status of Macaronesia as a marine biogeographic unit during the LIG was examined and our scientific understanding of how this unit evolved is improved. The analysis shows that during the LIG, the molluscan faunas of the Canary and Cabo Verde archipelagos were part of the same tropical Late Pleistocene Mediterranean West-African Province, whereas those in the Azores, Madeira and Selvagens archipelagos would be included in the subtropical Late Pleistocene French-Iberian Province. This contrasts with the present-day scenario, where the subtropical/warm temperate Azores and "Webbnesia" marine ecoregions (Lusitanian province) are biogeographically distinct from the Cabo Verde biogeographic subprovince, which in turn belongs to the West African Tropical biogeographic province. A further analysis of the coherence of "Macaronesia" as a marine biogeographical unit was accomplished by coupling Pliocene, LIG, and present-day data, showing that the term "Macaronesia", and for the marine realm, should only be used in a geographical connotation.