ON THE ORIGIN OF CAULERPA-TAXIFOLIA IN TH E MEDITERRANEAN-SEA

The Ulvophycean alga, Caulerpa taxifolia (Valh) C. Agardh, was first d iscovered in the Mediterranean Sea off the coast of Monaco in 1984; it was first observed in front of the Oceanographic Museum where it was cultivated for display in the aquaria. The species then began to sprea d rapidly from the northern part of the western Mediterranean to regio ns further south. In 1995, more than 90% of the colonized surfaces are still located within 10 km of the initial siting. An estimation of th e year of arrival of C. taxifolia in the 26 localities actually invent oried was made by means of chronological analysis of the expansion and a computer simulation of colony development. This invasive mediterran ean strain of Caulerpa taxifolia differs from tropical strains of C. t axifolia by its great resistance to low temperatures. An alternative h ypothesis, recently published by Chisholm et al. (1995) in the Comptes Rendus de l'Academie des Sciences [23], attempts to prove that Cauler pa taxifolia could came from the Red Sea, rather than from an aquarium and therefore its origin should be more ''natural'' and less preoccup ying. This hypothesis is based on the misidentification of a C. taxifo lia from Sicily as C. mexicana which would have supposedly ''metamorph osed'' into C. taxifolia. Chemical analysis and biogeographical data w ere presented to uphold this theory. Our data are not consistent with this hypothesis: we show that the C. mexicana identification was incor rect according to various criteria and that the caulerpenyne analyses most probably contained several mistakes (and consequently have no tax onomic significance). The biogeographic arguments do not seem very con vincing to us. Finally, the expression ''metamorphoses'', used for des cribing what most probably only corresponds to simple seasonal morphol ogic variations of a seaweed, is at least inappropriate.