Symptoms of Coral Reef Bleaching

The symptoms of coral bleaching are either expulsion of zooxanthellae from the coral host, or loss of pigmentation from the zooxanthellae cells (Venn et al., 2006). Most past investigations have stated that the coral polyps initiate the expulsion of zooxanthellae, but recent studies provide evidence suggesting that the expulsion of zooxanthellae is initiated by the zooxanthellae themselves, rather than the corals (Trapido-Rosenthal, 2005). The studies found the zooxanthellae produced large quantities of nitric oxide synthase before bleaching occurs. This enzyme leads to nitric oxide production in host cells, a reactive molecule that can lead to expulsion of zooxanthellae.