Alleged Lessepsian foraminifera prove native and suggest Pleistocene range expansions into the Mediterranean Sea

Biogeographical patterns are increasingly modified by the human-driven translocation of species, a process that accelerated several centuries ago. Observational datasets, however, rarely range back more than a few decades, implying that a large part of invasion histories went unobserved. Small-sized organisms, like benthic foraminifera, are more likely to have been reported only recently due to their lower detectability compared to larger-sized organisms. Recently detected native species of tropical affinity may have thus been mistaken for non-indigenous species due to the lack of evidence of their occurrence in pre-invasion records. To uncover the unobserved past of the Lessepsian invasion—the entrance of tropical species into the Mediterranean through the Suez Canal—we collected sediment cores on the southern Israeli shelf. We deployed state-of-the-art radiocarbon techniques to date 7 individual foraminiferal tests belonging to 5 alleged non-indigenous species and show that they are centuries to millennia old, thus native. Two additional species previously considered non-indigenous occurred in centennial to millennia-old sediments, suggesting their native status. The evidence of multiple tropical foraminiferal species supposed to be non-indigenous but proved native in the eastern Mediterranean suggests either survival in refugia during the Messinian Salinity Crisis (5.96-5.33 million years) or, more likely, dispersal from the tropical Atlantic and Indo-Pacific during the Pleistocene. In the interglacials of this epoch, higher sea levels may have allowed biological connectivity between the Mediterranean and the Red Sea for shallow-water species, showing that the Isthmus of Suez was possibly a more biologically porous barrier than previously considered.