Article

The results of a study carried out on the epiflora of a rhodolith bed from the Ustica Island Marine Reserve (Mediterranean Sea) are herewith presented. A list of 117 taxa at specific and infraspecific level (4 Cyanophyceae, 80 Rhodophyceae, 8 Ulvophyceae, 2 Chlorophyceae and 23 Phacophyceae) has been obtained, among which Alsidium corallinum C. Agardh is a new record for the Island of Ustica. Among Rhodophyceae, eight hodolith-forming taxa have been recognised; Lithophyllum, Lithothamnion, Neogoniolithon and Phymatolithon were the predominant genera. The calculated Rhodophyceac/Phacophyceac index value of 3.5 shows evi- dence of the high abundance of the red algae and of the subtropical character of this flora The floristic composition of this rhodolith bed could suggest the presence of the facies com- monly known in the Western Mediterrancan as “Free Melobesiae”, of which the Phymatholitho-Lithothamnietum corallioidis association (Giaccone 1965) Giaccone 1994 represents the typi- cal aspect. Moreover, the transitional position of this community, probably due t0 a locally ‘occurring combination of both climatic and edaphic factors, has been demonstrated.