Spread of the introduced tropical green alga Caulerpa taxifolia in northern Mediterranean waters

The first report of Caulerpa taxifolia in the Mediterranean is from 1984. The alga was found on the rocky shore at Monaco, below the Oceanographic Museum, where it had been on display in tropical aquaria. Within five years, there was an abundance of C. taxifolia on the shores around the first point of observation. In 1987, C. taxifolia appeared on the French coast, 3 km east of Monaco, at Cap Martin. By late 1991, 30 ha of shore in the vicinity of Monaco was covered with the alga. New points of colonization were in Livorno, Italy, 240 km east of Monaco, and to the west at Agay, Le Lavandou, Hyères, Toulon, Les Lecques, Saint Cyprien, 50 to 370 km from Monaco. The westernmost point of colonization, noted in September 1992, was 600 km from Monaco, at Majorca (Balearic island, Spain). Most types of substrata, between 0 and 50 m depth, are susceptible to colonization by C. taxifolia. Seaweed and seagrass populations on the coasts of Monaco and Cap Martin have been significantly reduced or destroyed because of invasion by C. taxifolia.