Climate Optimum rejuvenates the Mediterranean marine world.

The Mediterranean, a sea with an already eventful history, is again undergoing an extreme change. A combination of general warming of the Mediterranean Sea and contact with the Indopacific world through the Suez Canal has set the stage for massive changes in the biota that inhabit this sea. For over a century, tropical species of all taxa have been migrating back into the Mediterranean, suggesting a duplication or restoration of a mid-Pliocene Piacenzian or late Miocene Tortonian situation. Test cases are presented in three major taxa. It is not a serial invasion by individual rogue exotic and damaging species, as often wrongly assumed and asserted. Despite its unique biogeographic magnitude being recognized, an opportunity to study the progress of this phenomenon is being missed. This is because of the changed priorities in research, the acute taxonomic impediment and to the geopolitical difficulties in cooperation. Nonetheless, the limitations of the restoration process are defined and a careful future outlook is presented.