Medium-term effects of die-off of rocky benthos in the Ligurian Sea. What can we learn from gorgonians?

Mediterranean Sea ecosystems are experiencing a phase of major modifications owing to the fast increase in several disturbances such as pollution, eutrophication, habitat destruction, over-fishing, income of alien species, and climate change. One of the main problems in recent years is that global warming seems to intensify the effects of all the above-mentioned disturbances, dramatically reducing the biodiversity of the basin. The ever more frequent mass mortalities that are affecting shallow coastal environments are rapidly reducing the biomass of several filter feeders and both sponges and gorgonians are the most endangered taxa. In this paper we review the most recent episodes of mass mortality, mainly involving sea fans, and discuss the possible effects that the loss of these organisms can have on benthic assemblage structure. The data presented here are referred mainly to the study case of the MPA of Portofino (Ligurian Sea, Italy).