Marine biodiversity in the Mediterranean in the era of global warming

Abstract

The Mediterranean is a semi-enclosed temperate to locally warm sea. It is a hotspot of species, functional and ecosystem diversity, characterized by a high rate of endemism and a number of unique ecosystems. Between 12,000 and 17,000 marine species have been reported in the Mediterranean. Only one species is totally extinct and less than ten are extinct in the Mediterranean but still present elsewhere. In contrast, many species are functionally and/or regionally extinct. The progressive arrival of a thousand non-native species has in fact considerably increased the ε species diversity of the Mediterranean, contrary to the naive beliefs of some environmentalists. Several of the emblematic ecosystems of the Mediterranean （e.g. the dunebeach- banquette ecosystem, the Lithophyllum byssoides algal rim, the seagrass Posidonia oceanica meadow, the reef fucalean forests and the coralligenous） are currently in decline. Finally, the functioning of ecosystems （relative abundance of key species, carbon and nutrient flows, food webs, and interactions between ecosystems） has been profoundly altered. The causes of this impact on biodiversity are various; the three major causes are coastal development, overfishing, and biological invasions. Global warming is beginning to play a role, which will increase significantly over the course of the 21^st century, but it is currently far behind other human-induced causes. The concern over the growing and irreversible effects of global warming is totally justified; but the underestimation of other threats derives from issues which may be political or related to human perceptions and science funding, and which are discussed here.