Microalgae: a model to investigate the ecotoxicity of the green alga Caulerpa taxifolia from the Mediterranean sea

The spectacular development of the green alga Caulerpa taxifolia (Vahl) C. Agardh, introduced in the Mediterranean in 1984, represents a biological pollution which threatens the biodiversity of the marine ecosystem. The weak pressure from grazers and the presence of repulsive secondary metabolites make the problem worse. Whereas the anti-appetant effect of these metabolites is well known, their role in competition between algae has not been extensively studied. Using a microalgal model representing the initial stage of the marine food chain, we studied the effects of C. taxifolia metabolites. We showed that organic extracts of C. taxifolia and caulerpenyne inhibit or delay the proliferation of several phytoplanktonic strains to various degrees. Seasonal variations of the toxicity were observed with a maximal effect in the summer. Experiments with Dunaliella minuta showed that caulerpenyne did not affect the protein content but strongly reduced that of the cell chlorophyll A.