Algal flora associated with a Halophila stipulacea (Forsskal) Ascherson (Hydrocharitaceae, Helobiae) stand in the western Mediterranean

Halophila stipulacea, a seagrass introduced into the Mediterranean Sea as a Lessepsian immigrant, is nowadays common in the eastern Mediterranean, and it was recently recorded in the western Mediterranean; very little informa tion is available about the algal flora associated with this species. Durin g a survey of a Halophila stipulacea stand at Vulcano Island (Eolian Island s, western Mediterranean), samples were collected at three depths (5 m, 15 m and 25 m) for identification of algal epiphytes. Thirty-six species of ma croalgae were found. The epiflora of the leaves consisted of 20 species, th e others being mixed with or entangled in the rhizomes. On the leaves, Cera mium tenerrimum, Dasya corymbifera, Polysiphonia cfr. tenerrima, Spyridia f ilamentosa, Chondria pygmaea and Laurencia sp. were the most common species ; between the rhizomes, Dictyota linearis was abundant. A differentiation o f the epiphytic assemblage between 5 m and the other depths was observed; t he 5 m samples were characterized by the abundance of Ceramium tenerrimum, Chondria pygmaea and Polysiphonia cfr. tenerrima, while at 15 m and 25 m La urencia sp., Dasya corymbifera and Spyridia filamentosa were the most commo n species. Epiphytic cover was generally very low. No rare species were fou nd among the epiphytes. In comparison with other Mediterranean seagrasses, Halophila stipulacea has a qualitatively and quantitatively poor epiphytic flora. In particular, the virtual absence of encrusting corallines is notew orthy. A fast turnover rate of the leaves is hypothesized to be the main re ason for this scarcity. Differences between this and other studies on epiph ytes of Halophila stipulacea stands are discussed. (C) Elsevier, Paris / If remer / CNRS / IRD.