Systematics and Ecology of the Hydroid Population of two Posidonia oceanica Meadows

Abstract. The ecology and systematics of the hydroid population of Posidonia oceanica meadows have been studied in two different zones of the Western Mediterranean. A new sampling method has been employed and the results obtained have been compared with those of a standard method. The distribution of the species and several morphological variations are pointed out. Depth-related faunistic zones are evidenced. The key-species of the Posidonia hydroid population arc individuated.