Résumé
The Mediterranean Sea is one of the biggest reservoirs of biodiversity in the world. Millions of people directly or indirectly depend on the ecosystem services it provides, in particular the provisioning of fisheries resources. Rather than a hot-spot of biodiversity, the Mediterranean Sea has now become a hot-spot of global change where climate change and other anthropogenic pressures (e.g., overfishing, pollution, habitat destruction) operate independently or synergistically to shape an altered Mediterranean Sea that may shift from the today picture. The set of physical-chemical changes triggered by climate change may disrupt the functioning of the biological components of ecosystems, from the individual up to the ecosystem scale, from the basis of the food webs (macrophytes, phytoplankton) up to the higher trophic levels (e.g., predator fish). Current research shows that the physiology and fish life history traits have changed, that fish distribution areas are moving northward and eastward, thus modifying the structure and the species composition of the communities. The dynamics of populations and food webs are modified as well, and species invasions increase at an unprecedented rate. Combined with fishing, climate change renders marine ecosystems more vulnerable to anthropogenic pressures, to natural hazards and to invasions by non-indigenous species. Although uncertainties remain with regard to the magnitude of expected ecological changes, the projections based on IPCC scenarios all confirm that climate change is a serious threat for the biodiversity and the sustainable exploitation of fishing resources in the Mediterranean Sea. This calls for the reinforcement of innovative and integrated research and assessment capacities to support an ecosystem-based management at the scale of the Mediterranean basin.