Rare video footage shows the violent act of coral bleaching, caused by high sea water temperatures forcing corals to expel the symbiotic algae.
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This high-speed video shows coral reacting to higher sea surface temperatures. It's seen convulsing in a process called "bleaching" - the coral's attempt to remove algae.
In normal conditions, algae living in the tissues of coral supplies it with up to 95 percent of its daily metabolic energy. But as sea temperatures rise, the algae becomes unable to photosynthesize and oxidizes, becoming toxic to the coral. Algae is expelled when coral is under stress.
Without the algae, the coral's white external skeleton becomes visible. Some corals can bounce back when temperatures fall but many die from long-lasting whitening.
In recent months the northern half of Australia's Great Barrier Reef, the world's largest coral reef ecosystem, suffered one of its worst bleaching events.