Blue-green algae (Cyanophyta) in marine coastal environments of the Sinai Peninsula; distribution, zonation, stratification and taxonomic diversity

Eighty-four species of blue-green algae were recorded from the intertidal zone of the Gulf of Elat (Aqaba) and four hypersaline coastal pools. Heterocystous forms (sixteen) were restricted to the intertidal, although significant rates of nitrogen fixation (acetylene reduction) were measured in non-heterocystous communities in coastal pools. Species distribution, the colour and surface morphology of thick mats are determined by salinity, frequency of wetting and desiccation.

Distinct horizontal zonation patterns occur in coastal pools. Coccoid and non-filamentous forms such as Entophysalis and Pleurocapsa grow associated with gypsum crusts around the periphery of the pools, while filamentous forms (Lyngbya, Microcoleus) become abundant towards the central regions.

Complex stratification is apparent in many communities. In different coastal pools mat communities have a similar structure; Lyngbya aestuarii and pennate diatoms at the surface, then coccoid blue-green algae (Aphanorhece, Synechococcus), a bright green layer of Microcoleus chthofloplastes and finally deeper layers of phototrophic bacteria. In mangrove forests, Scytonema and a number of species of Rivulariaceae form conspicllous growths on aerial pneumatophores while non-heterocystous forms are restricted to the sediment surface.