Neogene history of Sporolithon Heydrich (Corallinales, Rhodophyta) in the Mediterranean region

Most modern species of Sporolithon live in tropical and subtropical areas and only one species of the genus, S. ptychoides, occurs in the Mediterranean Sea. The scarce present-day populations of Sporolithon in the Mediterranean region are relics of a long history of the genus in this area since the Early Cretaceous. Analysis of data from the palaeontological literature, combined with the study of both fossil samples and Recent ones collected from Italy and Spain, shows that during the Miocene variations in the number of Sporolithon species in the Mediterranean region parallel changes in global temperature. After a maximum species richness in the Langhian (early Mid Miocene), coincident with the Miocene climatic optimum, the number of species decreased to just two before the Messinian Salinity Crisis. This marked decline follows the global cooling event that began at around 14 Ma. The closure of the connections of the Mediterranean region with the Indian Ocean during the Langhian left Mediterranean Sporolithon populations isolated from the main dispersal area of the genus. After the Messinian desiccation, a single species, S. ptychoides, re-invaded the Mediterranean Basin during the Early Pliocene and continues to inhabit this temperate sea today. The Atlantic Ocean is the most probable source of the re-invading Sporolithon plants.