Résumé
Transfer of harmful species is mediated by natural dispersal, ballast water discharges and by bivalve relocation. This results of increasing risk of coastal waters invasion by exotic species. In spite of some confusion in relation to the identification of Alexandrium catenella, this dinoflagellate has been considered as a non-indigenous in Mediterranean. Our work aims to exhaustively characterise a strain of A. catenella (ACT00) isolated from Mediterranean waters using multiple criteria (genetic, morphology, toxin and pigment profiles) since this detailed information is still lacking. Examination of the morphology of the studied strain and of Alexandrium cells sampled during the bloom of May 2000 clearly showed the absence of the ventral pore between the plates 1' and 4' and the ability to form chains of up to eight cells during the exponential growth phase. This corresponds to the description of Alexandrium catenella (Whedon & Kofoid) Balech, 1985. Analysis of the nuclear rRNA fragment, including ITS I, the 5.8S rRNA gene, ITS2, and the D1/D2 28S rRNA genes revealed that the strain belonged to the A. catenella species from the Group IV (Temperate Asian clade). Toxin profile showed a dominance of C-toxins and gonyautoxins whereas saxitoxins and neosaxitoxins were absent. A. catenella is characterized by a pigment profile typical of peridinin containing dinoflagellates. Laboratory measured growth revealed a moderate growth rate of this species. The obtained reference data (morphogenetic, toxinic and pigment profile) on A. catenella from Thau lagoon are necessary in understanding of Alexandrium expansion in the Mediterranean waters and the geographic origin of this species.