MARINE VEGETATION OF THE MUSERI AND ENTEDEBIR ISLANDS (DAHLAK ARCHIPELAGO, RED SEA)

Abstract

The intertidal and shallow subtidal marine vegetation of two uninhabited islands in the Dahlak Archipelago, southern Red Sea, is described. The vegetation of these habitats is representative of the entire Archipelago, except for its seaward periphery. Under the highly sheltered conditions prevailing in most of this area, life in the intertidal and in the shallows is rather depauperated, the upper intertidal levels being mostly affected. On the rocky shores, the rarity of periwinkles is the most striking feature at these levels; a little lower down, barnacle belts are completely absent. Species diversity is rather low in the algal communities of the lower intertidal and the upper subtidal. Sciaphilic habitats at these levels harbor a more diverse vegetation, in which a number of species not previously reported from the Red Sea have been encountered. Mangal stands occur in the more sheltered sites. Avicennia marina belts are present in all mangal stands, Rhizophora mucronata belts occur in the highly sheltered sites on the leeward side of the Museri Island, while a single small stand of Ceriops tagal has been observed in a protected depression on the adjacent Desta Island. Bostrychietum, considered for a long time to be nonexistent in the Red Sea, has been found on A. marina aerial roots from an extremely sheltered location in the Melita Bay, Gulf of Zula, on the Ethiopian mainland coast. Caulerpetum serrulatae covers clayey bottoms in ca. 100 m deep troughs between the islands. It is exclusively composed of the low-light ecophene of Caulerpa serrulata , which differs from the normal, high-light form in bearing flat, ribbon-shaped assimilators.