Ostracod introductions show how the Lessepsian invasion is undermining the unique evolutionary history of the Mediterranean Sea

The Lessepsian invasion, the largest marine biological invasion from the Indo-Pacific to the Mediterranean via the Suez Canal, can be regarded as a partial human-induced reversal of the main direction of geological-time-scale biodiversity shifts from the Tethys Sea (present Mediterranean) to the Coral Triangle (southeast Asia and Melanesia) over tens of million years. To fully understand this macroevolutionary 'round trip', we need to investigate marine taxonomic groups with high fossilization potential and excellent fossil records. One such group is ostracods (Crustacea). While ostracods are well studied in regard to their Cenozoic biodiversity shifts, almost nothing is known about their role in the Lessepsian invasion. Here, we investigate present-day shallow-marine assemblages from surface sediment samples of the Israeli shelf (eastern Mediterranean) to investigate the occurrence of non-indigenous ostracods, identifying potentially eight such species. Based on our assessment of their geographical distribution, many of them belong to lineages that moved from Tethys to the central Indo-Pacific during the Cenozoic, before the counter migration to the Mediterranean. This is the first comprehensive assessment of ostracods during the Lessepsian invasion and an important step forward to a fuller understanding of this unique 'round trip' that undermines the biogeographical and evolutionary uniqueness of the Mediterranean ecosystem. This article is part of the theme issue 'The biosphere in the Anthropocene'.