The impact of the Messinian Salinity Crisis on Mediterranean marine biodiversity

The Messinian Salinity Crisis was the most extreme paleoenvironmental perturbation that has ever taken place in the Mediterranean. Approximately 7 million years ago, the straits connecting the Mediterranean Sea to the Atlantic Ocean started to restrict, and by 5.5 million years they closed. High-amplitude fluctuations in both temperature and salinity gave place to a hypersaline isolated Mediterranean, where marine organisms struggled to survive. In our recently published studies, we assembled and revised the marine fossil record from before and after the crisis in order to quantify the effect of the crisis on the biodiversity of the Mediterranean. We documented for the first time a clear perturbation of the biota even during the restriction phase, as well as a high degree of reorganisation of the marine ecosystem after the crisis, with most of the change in the taxonomic composition attributed to species turnover. Only a handful of endemic Mediterranean species may have survived the crisis. Furthermore, the present-day NW-to-SE decreasing gradient in species richness first appeared after the Messinian salinity crisis, suggesting that neither the distance from the Atlantic source nor the temperature gradient are the causes of the gradient today. Finally, we propose a model for the disruption in marine functional connectivity patterns, which is associated with the formation of a large evaporitic basin. This model can now be tested against the diverse ecosystem structures of the past that are associated with marginal marine basins formed due to the birth and death of the oceans.