Two-thirds of Great Barrier Reef hit by bleaching

Most of Australia’s Great Barrier Reef is being hit by coral bleaching, Australian marine park managers announced.

Since early March, oceanographers and marine scientists have been monitoring a spreading coral bleaching event affecting coral systems at the Great Barrier Reef Marine Park. In the marine park authority’s latest update, investigators said aerial surveys have uncovered bleaching hitting two-thirds of the world’s largest reef system.

Coral bleaching happens when abnormally high ocean water temperatures compel coral polyps, the animals that form hard reef skeletons, to expel the photosynthetic cyanobacteria that keep them alive. If warm ocean water conditions persist, the polyps will die, leaving the hard calcium carbonate skeletons behind and turning the coral white.

The Great Barrier Reef Marine Park Authority has pinned the latest bleaching event, the fifth to hit the park in under a decade, on abnormally high ocean temperatures recorded during the Southern Hemisphere summer. “Thermal stress continues to accumulate across the Marine Park,” the authority said. “However, sea surface temperatures have started to decrease as a result of high winds and swell.”

Though some ocean cooling has been recorded, the park authority remains concerned. “Thermal stress continues, with sea surface temperatures remaining above the long-term average across the Marine Park,” the agency said.

The park authority’s update says that southern portions of the GBR have been hit hardest. In addition to aerial surveys, teams of divers have been sent to investigate the situation up close. “A total of 107 in-water surveys were conducted in the Marine Park between 6 March–13 March,” the update said.

The authority is also keeping an eye on concerning outbreak of crown-of-thorns starfish. The starfish is a voracious predator of coral.

The increasing frequency of coral bleaching episodes at the Great Barrier Reef has prompted the United Nations Educational, Scientific and Cultural Organization (UNESCO) to consider downgrading the Great Barrier Reef’s World Heritage Site status to “in danger.” Australia narrowly convinced UNESCO to forgo that designation last year.

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