Preliminary survey of toxicity of the green algaCaulerpa taxifolia introduced into the Mediterranean

Caulerpa taxifolia (Vahl) C. Agardh (Ulvophyceae, Caulerpales) is an alga of tropical origin that was accidentally introduced into the Mediterranean sea in 1984, where this species can reach an abundance that has never been described in tropical endemic regions. It is known that caulerpacean algae can develop an efficient strategy against grazers consisting 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 fromC. taxifolia from the Mediterranean.Toxicity was evaluated on three models: mice (lethality), mammalian cells in culture (cytotoxicity) and sea urchin eggs (disturbance of cell proliferation). Aqueous extracts are only active on fibroblasts and mice. In the three toxicity models a seasonal variation of toxicity is observed for the crude methanol extract as well as a decrease of this activity whenC. 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 fibroblasts whereas taxifolial A and D are inactive or only weakly toxic. Among the four tested compounds caulerpenyne, the major metabolite ofC. taxifolia, is the most active on sea urchin eggs. Caulerpenyne may therefore represent an ecological risk for microorganisms and the eggs of multicellular animals living close to this alga. The ecological impact of this toxicity on marine organisms and the interaction of this alga with the herbivorous fauna are discussed.