Known and unknown terrestrial arthropod fauna of La Réunion Island, Indian Ocean

A major part of La Reunion Island has been included on the World Heritage List of the United Nations Educational, Scientific and Cultural Organization (UNESCO) for its unique landscapes and its outstanding biodiversity. However, there is a lack of knowledge on the arthropod diversity. For this reason, an up-to-date census of Reunion’s terrestrial arthropods was undertaken. Of the 3369 species that are reported from Reunion, 31% are endemic to the island and 40% are endemic to the Mascarenes. A diversity ratio between the numbers of described and expected species in the world was established and then applied to the numbers of reported species in Reunion to estimate the total expected numbers of species on the island. The results predict that between 6751 and 10,812 species of terrestrial arthropods are present in Reunion and that 62% of species remain to be discovered. However, some groups appear underrepresented as expected for Darwinian islands that should be originally composed by species with abilities to colonize remote places. Considering the global biodiversity decline and the numerous threats on Reunion’s natural habitats, this article emphasizes the crucial need for conservation of terrestrial arthropods and strongly encourages an increase in the list of protected arthropods.