341 © 2014 J. Cramer in Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, www.borntraeger-cramer.de Germany. DOI: 10.1127/0029-5035/2014/0156 0029-5035/2014/0156 $ 13.00 Nova Hedwigia Vol. 98 (2014) Issue 3–4, 341–392 published online January 14, 2014; published in print May 2014 Article C Benthic marine algae of the Arabian Gulf: a critical review and analysis of distribution and diversity patterns David Michael John 1* and Roda Fahad Al-Thani 2 1 Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK 2 Department of Biological and Environmental Sciences, College of Arts and Sciences, Qatar University, POB 2713, Doha, Qatar With 1 figure and 3 tables Abstract: The Arabian Gulf is an extremely inhospitable and physiologically-stressful environment for marine organisms since they are exposed to the widest range and the highest sea temperatures in the world, as well as high salinities. The present paper assembles and, as far as is possible without extended herbarium study, critically examines the status of all records of three phyla of marine benthic algae (Chlorophyta; Ochrophyta: Phaeophyceae and Xanthophyceae; Rhodophyta) and undertakes a taxonomic and nomenclature revision. All new records for the United Arab Emirates are based on material mostly collected in the 1980s by Dr Frances Dipper and Carolyn Lehmann. The provisional analyses of seaweed diversity and distribution patterns are based on presence-absence data. These are discussed in relation to key environmental variables, length of coastline and proportion of suitable habitats for benthic algae, with attention drawn to gaps due to unevenness of sampling. The diversity of the benthic algal flora is greater in the southern Gulf (Arabian coast) with about 130 species in common to the Iranian and Arabian side. Discussed are factors accounting for the relatively low algal diversity (282 spp.) of the Gulf and these include natural environmental stressors, relatively recent geological age of the basin, isolation and sampling intensity. The benthic algal flora of the Arabian Gulf represents an impoverished subset of that of the Indian Ocean. Key words: Arabian Gulf, benthic marine algae, distribution, taxonomic revision, diversity. Introduction The Arabian/Persian/'Gulf' is bordered by Iran, Iraq, Kuwait, Saudi Arabia, Bahrain, Qatar, the United Arab Emirates (UAE) along with part of the coast of northern Oman. The first authoritative account of the benthic algae of this semi-enclosed sea was *Author for correspondence; e-mail: d_m_john@ntlworld.com