Rising sea temperatures force corals to expel their pigmented algae, causing coral bleeching.

Algae called zooxanthellae live within corals and give them their beautiful colour.
In return for a safe sunny home, the zooxanthellae eat the nitrogen waste that the coral produces and turn sunlight into sugars by the process of photosynthesis. The sugars produced by the zooxanthellae make up 98 per cent of the coral’s food.

Rising water temperatures block the photosynthetic reaction that converts carbon dioxide into sugar. This results in a build-up of products that poison the zooxanthellae. To save itself, the coral spits out the zooxanthellae and some of its own tissue, leaving the coral a bleached white.

The bleached coral can recover, but only if cooler water temperatures return and the algae are able to grow again. Without the zooxanthellae, the coral slowly starves to death.

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