Seaweed species diversity in South Africa

A dataset is presented on the diversity of South African seaweed species and their distribution in contiguous 50-km coastal sections, to demonstrate current knowledge of the flora in various coastal regions. The coastline has a rich flora, consisting of some 800 species. The South Coast has the highest species diversity (between 250 and 300 species in each section) relative to the West Coast (about 140 species per section) or the East Coast (about 200 species per section). There is a considerable increase in the number of species (>240 species per section), particularly in the green algae, in the easternmost regions that border the tropics. An analysis of seaweeds present in six small stretches of coastline shows that these sites contain 80-90% of the species in the West and South coastal sections, but only 60% of species over the entire coastline. Therefore, successful conservation of relatively few sites could theoretically preserve the majority of the seaweed flora. Many of the species missing from these detailed collections are subtidal, a habitat that is generally undersampled, particularly on the South and East coasts. Although species diversity is becoming relatively well known, systematic studies on many groups, using modern techniques, are needed. Detailed core distribution data for many species are lacking, and there is no national plan for seaweed systematics or herbarium collections. The distributions of green algae are particularly poorly known. Detailed systematic and biogeographic investigations on the overlap between the seaweeds of the temperate South Coast and those of the tropical Indian Ocean are necessary, and these should include subtidal collections and vegetation descriptions.