To be alive or not to be alive: Radiocarbon data provide new perspective on species diversity in the Caspian Sea

The Caspian Sea is undergoing a severe biodiversity crisis. However, estimates of current extinction rates are difficult to obtain due to the lack of reliable pre-Anthropocene baseline data. For example, because the majority of endemic gastropod species was described from "fresh looking" shells, it remains unclear which species still existed prior to the Anthropocene. This study therefore used the species-rich microgastropod family Hydrobiidae to assess the extent to which endemic species were collected alive during the Anthropocene. Literature and database searches were performed. In addition, 14C dating was conducted on "fresh looking" shells collected in the Caspian Sea during the last 150 years. The literature review revealed that 75% of the "recent" species are only known from empty shells and 25% were recorded with a soft body. The 14C data showed that all "recent" specimens examined had an age between 1624 cal BC and 1888 cal AD. Two species studied predate the beginning of the Anthropocene. Two other species potentially or likely existed during the Anthropocene. This suggests that the number of endemic species still present at the beginning of the Anthropocene is lower than previously thought. The data also suggest that there was a substantial loss of species between the late 18th century and the 1950s and that only two endemic hydrobiid species have recently been found alive. These findings further contribute to the notion of a severe biodiversity crisis in the Caspian Sea. For accurate estimates of current extinction rates of Caspian Sea gastropods, pre-Anthropocene biodiversity data need to be further corroborated. Particularly, studies are required to clarify the taxonomic status of the dubious taxa and a possible "collection crisis" in the Caspian Sea due to decreasing sampling efforts in recent decades. In addition, comprehensive IUCN assessments are urgently required.