Distribution and phenology of the marine phanerogam Posidonia oceanica in the Pagassitikos Gulf, Greece HELEN AMOUTZOPOULOU-SCHINA* and SAVAS HARITONIDIS Department of Botany, School of Biology, Aristotle University, 54124 Thessaloniki, Greece Abstract Marine phanerogams are spread all over the world. Five different species exist in the Mediterranean. In Pagassitikos Gulf, a shallow semi-closed embayment in the western Aegean Sea (Greece), four species are encountered: Posidonia oceanica (L.) Delile, Cymodocea nodosa (Ucria) Ascherson, Zostera noltii (nana) Hornemann and Halophila stipulacea (Forsskaϊl) Ascherson. The latter is a Lessepsian immigrant, which entered the eastern Mediterranean through the Suez Canal, after its opening (1864). The distribution and ecology of marine phanerogams in Pagassitikos Gulf are studied, with special emphasis to Posidonia oceanica primary production and epiphytes. Shoot density of P. oceanica meadows, number of leaves per shoot, Leaf Standing Crop, Leaf Area Index, coefficient A and epiphytic algae of P. oceanica are the main results that are presented below.   < back .