Résumé
During the past century dramatic changes in the composition and structure of species assemblages have been observed worldwide. These changes took a sharp increase in recent years. Global changes such as climatic changes and species introductions are superimposed on more or less local habitat degradation, pollution and overexploitation. A detailed knowledge of the taxonomic composition of the flora and fauna at a local scale is important because it represents the only mean to assess subtle changes in the distribution and abundance of species, in particular of rare species. The present study discusses 15 interesting macroalgal species from the French Mediterranean coast. Among them, Antithamnion amphigeneum, A. piliferum, Cordylecladia guiryi, Goniotrichiopsis sublittoralis, Jania adhaerens, Laurencia chondrioides and Phyllophora sicula are reported and described for the first time from the region and 7 species are considered as introduced. For each species, the geographical distribution and the ecology are discussed.