Seaweed diversity patterns in Sub-Saharan Africa John J Bolton 1 , Olivier De Clerck 2 & David M John 3 1 Botany Department, University of Cape Town, Rondebosch 7701, South Africa: Bolton@botzoo.uct.ac.za 2 Ghent University, Research Group Phycology, Biology Department, Krijgslaan 281 S8, 9000 Ghent, Belgium: Olivier.declerck@Ugent.be 3 Department of Botany, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. D.John@nhm.ac.uk Abstract A proper understanding of inshore marine ecosystems cannot be obtained without a thorough knowledge of marine vegetation. This paper summarises our knowledge of species diversity patterns of marine macroalgae in Sub-Saharan Africa, highlighting gaps. In Tropical East Africa the seaweed floras of Somalia and Mozambique are not well known. In Tropical West Africa, only a small number of countries are well-collected, although recent advances, including web-based systems, are ensuring that the information which is available can be more easily accessed. South Africa and Namibia have quite well documented seaweed floras, although detailed collections, especially in the subtidal, or detailed studies of taxa, particularly using molecular methods, anywhere in the region are likely to bring up new records and lead to the discovery of species new to science. South Africa has a very rich seaweed flora (ca. 850 species), due to the presence of species from three of the four major biogeographic regions in sub-Saharan Africa occurring within its borders. Figures for reasonably well- studied countries in Tropical East Africa are more than 400 species, whereas much of Tropical West Africa has lower numbers (e.g. 200 species in well-studied Ghana). Factors which may account for these major differences in seaweed diversity patterns are discussed. Training workshops in Africa are necessary to recruit a body of local scientists able to identify and work with seaweeds, and to make the wealth of information in the international literature available to African marine scientists. A network of national herbaria should contain a collection of correctly identified seaweed species. Introduction Seaweeds are particularly useful organisms for studying diversity patterns and planning the conservation and sustainable use of inshore marine resources, and are also useful as indicators of climatic change (see John & Lawson, 1997; Van der Strate et al. 2002; Bolton et al. in press). They are relatively easy to collect, fixed to the substratum, often form relatively stable assemblages, and have relatively similar species numbers in richer temperate and tropical regions. There are four major seaweed floras represented in sub-Saharan Africa. The distinctive but depauperate Tropical West African flora is separated from the species-rich North African temperate flora by a transitional zone extending from about Cap Vert in Senegal to Cap Blanc in Mauritania. South of the equator the West African Flora is very depauperate and only abruptly changes to a temperate flora in northern Namibia (John & Lawson, 1991). The Tropical East Africa flora is more species-rich, and represents only a portion of the much larger flora of the Indo-West Pacific. The latter represents the largest marine biogeographical region on earth, with the greatest diversity of inshore benthic organisms. At the southern tip of the continent are two distinct temperate regions. The west coast of South Africa and the 229