MEDITERRANEAN CAULERPA-TAXIFOLIA AND CAULERPA-MEXICANA (CHLOROPHYTA) ARE NOT CONSPECIFIC

In 1984, Caulerpa taxifolia (Vahl) C. Agardh was reported along the co ast of Monaco, Over the past decade it has spread along 60 km of the M editerranean coastline and presently represents a potential risk. to b iodiversity, Several explanations have been advanced regarding the pre sence of C. taxifolia in the Mediterranean. One hypothesis maintains t hat the alga was introduced accidentally into the sea at Monaco, where it has been used as a decorative alga in aquaria. Caulerpa taxifolia has not been reported in earlier marine floras of the Mediterranean an d ifs sudden appearance has suggested that it may be a recent introduc tion. Another hypothesis proposes that C. taxifolia and Caulerpa mexic ana Sonder ex Kutzing are morphological variants of one another and he nce conspecific taxa. Caulerpa mexicana has been found in the eastern. Mediterranean since at least 1941. In order to establish the taxonomi c identities of these taxa, individuals from five populations of C. ta xifolia and four populations of C. mexicana were collected from within and outside of the Mediterranean. Comparative DNA sequence analysis o f the nuclear ribosomal cistron, including the 3'-end of the 18S, ITS1 , 5.8S, and ITS2 regions, show clear phylogenetic separation of the tw o taxa using parsimony and maximum likelihood analyses. Separation is maintained whether the analyses are based on just the more conserved 1 8S data or just the fast-evolving spacers. The two species are thus no t conspecific. For specimens of uncertain identity (i.e. taxifolia-mex icana intermediates), a PCR diagnostic amplification can easily be per formed because the ITS1 in C. taxifolia is 36 nucleotides shorter than the ITS1 in C. mexicana. Whether or not C. taxifolia has been present for a longer period of time in the marine flora, either as a cryptic endemic species or as the result of one or more introductions, represe nts an additional hypothesis that will require identification of bioge ographic populations from throughout the world, as well as a populatio n-level study of the Mediterranean region.