Peter, N.Semba, M.Lugomela, C.Kyewalyanga, M.S.2021-03-302021-03-302018Peter, N., Semba, M., Lugomela, C. and Kyewalyanga, M.S. (2018). The influence of physico-chemical variables on the spatial and seasonal variation of chlorophyll-a in coastal waters of Unguja, Zanzibar, Tanzania. Western Indian Ocean Journal of Marine Science, 17(2): 25-34.http://hdl.handle.net/20.500.11810/5568Chlorophyll-a (Chl-a) concentrations were measured at four sites around Unguja, Zanzibar during the northeast (NE) and southeast (SE) monsoon seasons. Data for Chl-a, nitrate, phosphate, ammonia, dissolved oxygen, sea sur face temperature, pH and salinity were collected once a month from March 2008 to March 2009. The SE monsoon had insignificantly higher Chl-a compared to the NE monsoon season when Chl-a for Bawe, Chumbe, Pongwe and Mnemba were combined (W = 234, p = 0.93). The drivers of high Chl-a during the SE monsoon were ammonia and nitrate. Results from individual sites showed that Pongwe and Mnemba had higher median Chl-a during the SE than the NE monsoon season. Temperature, dissolved oxygen and ammonia were the major factors that influenced high Chl-a at these sites. In contrast, Chumbe and Bawe had higher median Chl-a during the NE- than the SE mon soon season. The major factors influencing high Chl-a in the NE at Chumbe and Bawe were high levels of nutrients, mainly from sewage effluent and various human activities around the coast in Zanzibar town. The interaction of Chl-a between monsoon seasons (NE and SE) and sites (Bawe, Chumbe, Pongwe and Mnemba) was insignificant (F(1,3) = 1.3144, p = 0.2949). The principal component analysis revealed that different physical and chemical environmental variables affect Chl-a concentration over time and location.enChlorophyll-a, monsoon seasons, physical-chemical variables, ZanzibarJournal ArticleDOI: 10.4314/wiojms.v17i2.3