Great Barrier Reef suffers through record-breaking bleaching event

The Great Barrier Reef, located off the northeast tip of Australia, is one of the natural wonders of the world. In addition to providing vast ecological benefits, the Great Barrier Reef also is a tourist hotspot for Australia. It’s worth $5 billion annually and employs close to 70,000 people. And it has had a bad year. A long stretch of weeks with unusually warm waters, partly linked to El Niño, have led to heat stress and widespread bleaching across the 2,300-kilometer-length of the Great Barrier Reef.

Location of the Great Barrier Reef off of northeastern Australia. Climate.gov image based on data from NOAA Environmental Visualization Lab.

Coral bleaching refers to the process where heat-stressed corals expel the colorful algae that usually live within their tissues. When water temperatures increase, though, the coral turns into an angry landlord, ejecting their beneficial tenants. After the loss of their beneficial algae, the corals turn completely white. The problem? Those tenants make almost all of the corals’ food. If the algae are expelled and do not return, the corals will starve and die.

The current bleaching event is being widely described as the worst ever recorded along the Great Barrier Reef. Based on updates from Australian scientists on April 20, 2016, 93% of the reefs surveyed showed at least some bleaching. Of 900 reefs that scientists observed during a flyover, only 68 had escaped bleaching. Between 60 to 100% of corals on 316 reefs were described as severely bleached, almost all in the north.

Historically, the northern reefs—the most remote—have been the most pristine and the least degraded, both by humans and by past bleaching events. During this event, 81% of reefs in the north had severely bleached. The central reefs were 33% severely bleached, while reefs in the southern section were only 1% severely bleached, with a quarter not bleached at all.

A compilation of aerial and underwater video showing bleaching on Australia's Great Barrier Reef in April 2016. Video provided by the ARC Centre of Excellence for Coral Reef Studies.

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