Mediterranean corals through time: From Miocene to present

Stony corals, especially scleractinians, are a recurrent component of the benthic fauna of the Mediterranean basin and its Mesozoic-to-Cenozoic precursors. Both morphological and geochemical features of coral skeletons place these organisms among the most important natural paleoarchives of the Mediterranean geological history. The present day low diversity of the Mediterranean scleractinian fauna (25 genera and only 33 species) strikingly contrasts with its high diversity in the Early-Middle Miocene (over 80 genera and hundreds of species). The decline in coral richness has occurred since the late Middle Miocene onwards. This impoverishment trend was not linear, but abrupt in shallow-water environments during and immediately after the Late Miocene and more gradual since the Pliocene onwards. At the end of the Miocene, the Mediterranean coral fauna underwent a drastic modification that led to the disappearance of almost all zooxanthellate corals and the well-established shallow-water coral-reef province. However, the generic diversity of azooxanthellate and deep-water corals did not undergo significant modifications, that were instead much stronger at the end of the Pliocene and of the Pleistocene. Indeed, before the Calabrian stage, all remnant Indo-Pacific-like azooxanthellate genera disappeared and a clear NE Atlantic affinity was established, whereas at the Pleistocene - Holocene boundary, there was a clear reduction in psychrospheric deep-water taxa. The causes that led to the impoverishment of the Mediterranean coral fauna diversity are complex and not all fully understood. However, there is a clear link between the coral diversity decrease, the gradual northward shift outside the tropical belt of the Mediterranean region, and the major climate modifications on a global scale during the last 20 million years.