Coral are bleaching along the entire Great Barrier Reef

(credit: Dorothea Bender-Champ for ARC Centre of Excellence for Coral Reef Studies)

Coral reefs are about as colorful as the ocean gets—except when they bleach. Overly warm water can cause corals to spit out the colorful, photosynthetic, single-celled symbiotes that live inside them and produce most of their food. If the heat passes before the corals starve to death, their symbiotes can return, bringing color and health back to the coral.

As the globe warms, widespread bleaching events are occurring with disturbing frequency. These tend to occur during times of El Niño conditions in the Pacific, which add a temporary boost to the warming water at some reefs. The current record-strength El Niño is sadly no exception.

Researchers contributing to Australia’s National Coral Bleaching Taskforce recently completed a survey of the state of the iconic Great Barrier Reef. The results show that it is currently experiencing the worst bleaching event we’ve ever seen there. Overall, 93 percent of the Great Barrier Reef has bleached to some degree. The northern half of the reef has been hit the hardest, with about 80 percent categorized as severely bleached. The far southern portion has escaped the warmest water, and the area of severe damage there drops to around 1 percent.

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