An overview of historical harmful algae blooms outbreaks in the Arabian Seas Maryam R. Al Shehhi ⇑ , Imen Gherboudj, Hosni Ghedira Institute Center for Water and Environment (iWATER), Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates article info Article history: Available online 16 July 2014 Keywords: HABs Red tide Arabian Seas Arabian Gulf Gulf of Oman abstract Harmful algae blooms (HABs), often composed of oceanic plants called phytoplankton, are potentially harmful to the marine life, water quality, human health, and desalination plants, a chief source of potable water in the Arabian Gulf. The last decade has seen a noticeable increase in the frequency of HAB out- breaks in the Arabian Seas. This increase is mainly caused by the unprecedented economic growth in the region. The increased human activities in the region have added more stress to the marine environ- ment and contributed to the changes observed in the properties of the marine ecosystem: high temper- ature and salinity, high evaporation rates, limited freshwater inflow, shallow nature, pollution. However, very few studies that cover the HAB outbreaks, causes, impacts and biological characteristics over the region have been published. This work presents a comprehensive overview of historical HAB outbreaks recorded in the region, and investigate their causes and impact, and seasonal variability. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The Arabian Gulf, the Gulf of Oman and the Arabian Sea, collec- tively referred to here as the Arabian Seas, have long been an important trade route (Hamza and Munawar, 2009; Nezlin et al., 2010; Richlen et al., 2010). Given their fragile ecosystem and their high risk of pollution, mapping and monitoring the quality and the physical and biological properties of these water bodies is increas- ingly needed by local, national and regional authorities (Hamza and Munawar, 2009; Reynolds, 1993; Richlen et al., 2010; Solomon et al., 2009). Currently, the most serious pollutants affect- ing the physical and biological quality of these water bodies are harmful algal blooms (HABs). HABs, commonly referred to as red tide in the literature, have been occurring more frequently in the Arabian Gulf during the last few years. Most often, they have been transported from the Ara- bian Sea and the Gulf of Oman which makes them a common threat to the region (Subba Rao and Al-Yamani, 1998). Their pres- ence has been detrimental to the water quality and its surrounding environment. These adverse impacts generally include, but are not limited to: (1) the death of large quantities of fishes and crusta- ceans such as in Kuwait (2001), Oman (2005) and UAE (2008) (Al-Busaidi et al., 2008; Glibert et al., 2002); (2) their effect on human health by causing respiratory irritation (Tomlinson et al., 2009); (3) the suspension of desalination plants’ operation, in some extreme cases, due to the high toxicity level in the water surround- ing the plant intakes such as the desalination plants in Kalba, Fujai- rah, Khor-Fakan and Ras-Al-Khaimah (Ghaleelah) as reported by the Ministry of Environment and Water in the United Arab Emir- ates (UAE Ministry of Environment and Water, 2011); and (4) the spread of a bad smell in the air resulting from the organic decom- position of dead plant algae, for instance the Fujairah incident in 2008. Several case studies have been investigated to give an overview of the red tide causes and impacts over the Arabian Seas. This paper presents a summary of the recent studies on this topic that were carried out over the region, including understanding the pat- tern of red tide occurrences and their impact on the regional mar- itime ecosystem, exploring the multiple factors causing their outbreaks, and analyzing their temporal/spatial variability (spe- cies, concentration) by correlating them with atmospheric/water variables (wind, dust, currents). 2. Arabian Seas description Fig. 1 shows the location of the Arabian Seas with typical water circulation patterns and freshwater sources. As shown in this fig- ure, even though they are interconnected, these seas have signifi- cantly different geometrical and physical characteristics which affect each other in different ways. http://dx.doi.org/10.1016/j.marpolbul.2014.06.048 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +971 2 810 9124. E-mail addresses: mralshehhi@masdar.ac.ae (M.R. Al Shehhi), igherboudj@ masdar.ac.ae (I. Gherboudj), hghedira@masdar.ac.ae (H. Ghedira). Marine Pollution Bulletin 86 (2014) 314–324 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul