Researcher have found that an imbalance of nutrients in reef waters can increase the bleaching susceptibility of reef corals. Corals are made up of many polyps that jointly form a layer of living tissue covering the calcareous skeletons. They depend on single-celled algae called zooxanthellae, which live within the coral polyps. The coral animal and the associated zooxanthellae depend on each other for survival in a symbiotic relationship, where the coral supplies the algae with nutrients and a place to live. In turn, the algae offer the coral some products of their photosynthesis, providing them with an important energy source. High water temperatures can block photosynthetic reactions in the algal cells causing a build-up of toxic oxygen compounds, which threaten the coral and can result in a loss of the zooxanthellae....