Since its first accidental introduction into the Mediterranean Sea, Caulerpa taxifolia (Vahl) C. Agardh has spread to six Mediterranean countries and has become a major ecological problem. On the basis of morphological and molecular studies (nuclear ribosomal internal transcribed spacer (ITS)), we report for the first time C. tax fblia on the Levantine coast (Gulf of Iskenderun, SE Turkey). Phylogenetic analysis revealed that the Iskenderun isolate differs from the invasive aquarium strain first observed in Monaco, and falls in another SW Pacific clade (NE Australia, New Caledonia). The introduction in Turkey by shipping (ballast waters or anchor gears of oil tankers) is possible because C. taxifolia was found in the Gulf of Iskenderun, which is a major Eastern Mediterranean petrochemical region. On the other hand, C. taxifolia strains are available in aquarium shops in Turkey, suggesting aquarium dumping as another possible cause. As far as the intense maritime traffic of the region is concerned, further dispersals of this exotic C. taxifolia strain in the Mediterranean Sea are to be expected. (c) 2007 Elsevier Ltd. All rights reserved.