Back-to-back severe bleaching events have affected two-thirds of the Great Barrier Reef.
The findings have caused alarm among scientists, who say the closeness of the 2016 and 2017 bleaching events is unprecedented for the reef, and will give damaged coral little chance to recover.
Scientists with the Australian Research Council’s Centre of Excellence for Coral Reef Studies last week completed aerial surveys of the world’s largest living structure, scoring bleaching at 800 individual coral reefs across 8000km.
The results show the two consecutive mass bleachings events have affected a 1500km stretch, leaving only the reef’s southern third unscathed.
Last year’s bleaching was concentrated in the reef’s northern third. The 2017 event spread further south, and was most intense in the middle section of the reef. Worse, this year’s mass bleaching, which was the second most severe after the 2016 event, occurred when there was no El Nino weather pattern.
Mass bleaching – a phenomenon caused by sea surface temperatures rising due to global warming – has occurred on the reef four times in recorded history.
Professor Terry Hughes, who led the surveys, said even the fastest-growing corals needed about 10 years to recover. He raised serious concerns about the increasing frequency of mass bleachings.
“The significance of bleaching this year is that it’s back to back, so there’s been zero time for recovery,” Hughes said.
“It’s too early yet to tell what the full death toll will be from this year’s bleaching, but clearly it will extend 500km south of last year’s bleaching.”
Last year, in the worst-affected areas to the reef’s north, roughly two-thirds of shallow-water corals were lost.
Hughes has warned Australia now faces a closing window to save the reef by taking decisive action on climate change.
The 2017 bleaching is likely to be compounded by other stresses on the reef, including the destructive crown of thorns starfish and poor water quality.
Tropical cyclone Debbie came too late and too far south for its cooling effect to alleviate bleaching.
Hughes said its slow movement across the reef was likely to have caused destruction to coral along a path up to 100km wide.
“It added to the woes of the bleaching. It came too late to stop the bleaching, and it came to the wrong place,” he said.
Some reef scientists are now becoming despondent. Water quality expert Jon Brodie said the reef was now in a “terminal stage”. Brodie has devoted much of his life to improving water quality on the reef, one measure used to stop bleaching.
He said measures to improve water quality were failing.
“We’ve given up. It’s been my life managing water quality. We’ve failed,” Brodie said. “Even though we’ve spent a lot of money, we’ve had no success.”
Brodie used strong language to describe the threats to the reef in 2017. He said the compounding effect of back-to-back bleaching, Cyclone Debbie, and run-off from nearby catchments should not be understated.
“Last year was bad enough, this year is a disaster year,” Brodie said. “The federal government is doing nothing really, and the current programmes, the water quality management is having very limited success. It’s unsuccessful.”
Others remain optimistic, out of necessity. Jon Day was a director of the Great Barrier Reef Marine Park Authority for 16 years until retiring in 2014.
Day, whose expertise lies in protected area planning and management, said the federal government’s approach to protecting the reef was sorely lacking.
He said it was taking too relaxed an approach to fishing, run-off and pollution from farming, and the dumping of maintenance dredge spoil.
The government was far short of the $8.2b needed to meet water quality targets. Australia was on track to fail its short-term 2018 water quality targets, let alone meet more ambitious long-term goals.
“You’ve got to be optimistic, I think we have to be,” Day aid. “But every moment we waste, and every dollar we waste, isn’t helping the issue. We’ve been denying it for so long, and now we’re starting to accept it. But we’re spending insufficient amounts addressing the problem.”
The Queensland tourism industry raised questions about the reliability of the survey, saying scientists had previously made exaggerated claims about mortality rates and bleaching.