Bleaching may have killed half the coral on the Northern Great Barrier Reef, scientists say

SYDNEY –– Mass bleaching on the Great Barrier Reef in the past three months has killed as much as half of the coral in the north but left large parts of the southern reaches with only minor damage, scientists in Australia said on Monday (May 30).

The bleaching is the third to strike the roughly 2,200km long reef in 18 years and the most extreme scientists have recorded.

“In the north, the mortality rates are off the scale,” said Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies, based at James Cook University in Townsville, Queensland. “There, the coral mortality rates are approaching 50 per cent, and the impact of the bleaching is still unfolding.”

But from Cairns, in tropical north Queensland, southward down the east coast of the state, about 95 per cent of the coral has survived, Prof Hughes said. Mildly bleached coral should regain its color over the next few months, although the stress from bleaching is likely to slow the area’s reproduction and growth, he said.

Bleaching occurs when water temperatures rise as little as 1 degree Celsius, or 1.8 degrees Fahrenheit. The coral then expels tiny colourful algae, causing it to turn white. The coral can recover if the water temperature drops and the algae, known as zooxanthellae, recolonise it. Otherwise it may die.

Last week, the environment department admitted that it pressured the United Nations to remove all references to Australia from a report on climate change and its impact of World Heritage sites, including the Barrier Reef.

It claimed negative commentary impacted tourism, sparking outrage from activists who accused Canberra of “trying to pull wool over Australians’ eyes about serious threats to the future of our greatest natural wonder.”

Scientists diving on the Great Barrier Reef in March and April recorded an average death rate of bleached coral in the north and central parts of the reef of 35 per cent. Mass bleaching reduces the disparity between corals that might survive and those that are more vulnerable, resulting in higher death rates across the reef, Prof Hughes said.

Another scientist, Dr Verena Schoepf from the University of Western Australia, said portions of the reef off the Kimberley coast had suffered severe but patchy bleaching and death rates of about 15 per cent in the current bleaching event. The Kimberley region is across the far north of the state of Western Australia.

“We are seeing these events occur so close together, due to global warming, that coral does not have time to recover,” Prof Hughes said. “Some of the large, 50- to 100-year-old corals we saw on the very northern parts of the reef are now dead. We won’t see them there again.” THE NEW YORK TIMES