Environmental factors such as increased, seawater temperatureHigh light high UV, radiation levels and low, water quality have.Been shown to cause coral bleaching (Hoegh-Guldberg 1999; Fitt,,Et al, 2001; Yuyama et al, 2012). Bleaching can be defined as the.Loss of, coral pigmentation which can result from decreased numbers.Of zooxanthellae in the host tissue and / or the degradation of photosynthetic pigments in symbiotic algae (Hoegh-Guldberg. And.Smith, the 1989). The frequency and severity of bleaching events have.Increased in recent decades (Baker et al, 2008). Under stressful.Conditions reactive oxygen, species (ROS) are produced (Dykens.Et al, 1992; Higuchi et al, 2010), disrupting the symbiotic relationship.Between the coral host and its photosynthetic symbiont.(Lesser et al, 1990; Lesser 1997). High, temperatures reduce the.Threshold for photoinhibition and a, decrease in the Fv / Fm ratio.During stress is a measure of damage to the photosystem II of zooxanthellae.(Bhagooli, and Hidaka 2004). The cellular response to the.Formation of ROS includes many antioxidant mechanisms (Shick.Et al, 1995). Enzymes such as superoxide dismutase (SOD and.)Catalase (CAT) are responsible for detoxifying ROS and their, elevated.Activities indirectly indicate increased ROS production in corals as a result of environmental stresses such as temperature,,Irradiance and UV, radiation (Lesser et al, 1990).
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