PRELIMINARY SURVEY OF TOXICITY OF THE GREEN-ALGA CAULERPA-TAXIFOLIA INTRODUCED INTO THE MEDITERRANEAN

Caulerpa taxifolia (Vahl) C. Agardh (Ulvophyceae, Caulerpales) is an a lga of tropical origin that was accidentally introduced into the Medit erranean sea in 1984, where this species can reach an abundance that h as never been described in tropical endemic regions. It is known that caulerpacean algae can develop an efficient strategy against grazers c onsisting of the synthesis of repulsive of toxic secondary metabolites : we report here the first study of the toxicity of purified secondary metabolites and raw extracts from C. taxifolia from the Mediterranean . Toxicity was evaluated on three models: mice (lethality), mammalian cells in culture (cytotoxicity) and sea urchin eggs (disturbance of ce ll proliferation). Aqueous extracts are only active on fibroblasts and mice. In the three toxicity models a seasonal variation of toxicity i s observed for the crude methanol extract as well as a decrease of thi s activity when C. taxifolia from the Mediterranean is kept in aquaria . Pure compounds exhibit different toxicity depending on the assay. 10 ,11-epoxycaulerpenyne is the most active substance on mice and fibrobl asts whereas taxifolial A and D are inactive or only weakly toxic. Amo ng the four tested compounds caulerpenyne, the major metabolite of C. taxifolia, is the most active on sea urchin eggs. Caulerpenyne may the refore represent an ecological risk for microorganisms and the eggs of multicellular animals living close to this alga. The ecological impac t of this toxicity on marine organisms and the interaction of this alg a with the herbivorous fauna are discussed