In the late summer 1999, an extensive mortality of gorgonians and other epibenthic organisms was observed in the Ligurian Sea (Mediterranean Sea) from the Tuscan Archipelago to Marseilles. Quantitative data from Tino Island and Portofino Promontory indicated that the proportion of affected gorgonians ranged from 60% to 100% in populations having a density of 9-27.8 colonies/m², suggesting that millions of sea fans died along the coast of Liguria. This mass mortality episode coincided with a sudden increase of sea water temperature down to more than 50 m depth. Laboratory analyses showed that the colonies stressed by high temperature also underwent extensive attack by microrganisms (protozoans and fungi), which are interpreted as opportunistic pathogens.