Macrophytobenthos des platiers rocheux intertidaux et semi-exposés da la région de Safi-Essaouira (Maroc occidental)

In 1990, a study of the phytobenthos of the rocky intertidal platforms in the Safi-Essaouira region (Sidi Boulbra, Western Morocco) was carried out at three sites. The intertidal zonation was analysed along permanent transects, and a qualitative and quantitative study of two characteristic units of the eulittoral vegetation - the vegetation belt of Fucus spiralis and the communities of Florideophyceae - was made. One hundred and twenty-nine macroalgal taxa and three phases were listed: 19 Ulvophyceae, 19 Fucophyceae, 1 Bangiophyceae and 93 Florideophyceae. The intertidal communities of the area are typical of semi-exposed and unpolluted platforms of Western Morocco, in the eulittoral zone, most of the typical Fucales that occur along the NE Atlantic coasts are absent, with the result that Florideophyceae are dominant. The composition and distribution of the communities are influenced by the short morphology (extensive platform, gentle slope and roughness degree), the substrate (sandstone), the occurrence of sediment and by high exposure to wave action. The vegetation belt of Fucus spiralis of Sidi Boulbra ranks floristically amongst the richest described in the NE Atlantic, and is characterized by the presence of southern species. The communities of Florideophyceae exhibit a mixture of exposed-shore, sheltered-shore and sand-tolerant species, resembling those described from SW Portugal. The dominant species change according to the season and environmental conditions. Over low-roughness platforms, an Osmundea, Gigartina (site 1) and a Leptosiphonia (site 3) community may be observed in winter-spring, and a Caulacanthus, Ceramium, Gelidium community in summer-autumn, Over extensive high-roughness platforms (site 2), this scheme is somewhat obscured by the development of varied Fucophyceae (Dictyotales, Sphacelariales). Moreover, any extensive destruction of eulittoral communities usually induces a green algal bloom (Ulvales). Amongst the common algae from Sidi Boulbra, several Gelidiales and Gigartinales are potentially commercial taxa.