Molecular evidence for extensive discontinuity between peracarid (Crustacea) fauna of Macaronesian islands and nearby continental coasts: over fifty candidate endemic species

Oceanic islands are recognized evolutionary hotspots for terrestrial organisms, but little is known about their impact on marine organisms’ evolution and biogeography. The volcanic archipelagos of Macaronesia occupy a vast and complex region in the Atlantic Ocean and may be particularly suitable to investigate marine island biogeography. In this study, we used mitochondrial DNA sequences (cytochrome c oxidase subunit I DNA barcoding region) to investigate the genetic differentiation between the populations from Webbnesia (i.e. Madeira, Selvagens and Canary Islands) and adjacent coasts (Azores, Continental Iberian Peninsula and Morocco) of 23 intertidal peracarid species. All species had high intraspecific genetic distances (>3%), reaching more than 20% in some cases. Between 79 and 95 Molecular Operational Taxonomic Units (MOTUs) were found in these species. Webbnesia populations displayed high genetic diversity and high endemicity, with 83% of the MOTUs being private to these islands, particularly La Palma and Madeira. Artificial community network analyses based on MOTU occurrence suggested higher similarity between Webbnesia and Azores than with adjacent continental coasts. These results reveal an unanticipated and strong biogeographic discontinuity of peracaridean fauna between Webbnesia and the Iberian Peninsula, a pattern that may occur in other groups of marine invertebrates in the region. We emphasize the unique genetic heritage hosted by these islands, underlining the need to consider the fine scale endemicity in marine conservation efforts.