Great Barrier Reef recovery unlikely after ‘catastrophic die-off’ caused by marine heatwaves, say scientists

‘The prospects for a full recovery to the pre-bleaching coral assemblages are poor,’ according to new study

The Great Barrier Reef is unlikely to recover from the marine heatwaves that wiped out much of its coral in 2016, according to a new study.

An assessment by a team of Australian researchers looked at the lasting impact of these devastating events, which killed close to a third of the coral living on the reef.

They found that while many corals had died immediately due to the heat stress, others perished over longer periods of time following the depletion of the algae that live inside them.

Corals are the basis of diverse ecosystems, supporting a myriad of other creatures, and the researchers found the die-off left these ecosystems in an unstable state from which they were unlikely to recover.

“The coral die-off has caused radical changes in the mix of coral species on hundreds of individual reefs, where mature and diverse reef communities are being transformed into more degraded systems, with just a few tough species remaining,” said Professor Andrew Baird, a coral expert at James Cook University and one of the co-authors of the study.

“The prospects for a full recovery to the pre-bleaching coral assemblages are poor,” the authors wrote in their paper, which was published in the journal Nature.

Professor Baird and his colleagues mapped 2,300km of the Great Barrier Reef, examining heat exposure and the resultant coral death.

Their study confirmed that coral death was highly correlated with the amount of bleaching and heat exposure, and that the northern part of the reef was the worst affected.

Significantly, many areas of the reef still appear to be slowly dying, and the replacement of dead corals is likely to take at least a decade.

The coral bleaching that struck the Great Barrier Reef has been described as the “longest, most widespread, and possibly the most damaging” on record.

“When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die,” said Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies, who led the study.

“Averaged across the whole Great Barrier Reef, we lost 30 per cent of the corals in the nine month period between March and November 2016.”

Bleaching is linked with global warming, as rising sea temperatures cause stressed corals to expel the algae that provide them with the energy they require to survive.

As these events are likely to continue, given current climate projections, scientists have called for “radical interventions” to help save the reefs.

Proposals under consideration include genetically engineered corals, geoengineering the atmosphere and even applying “sun shields” to the surface of the water to protect reefs from sunlight.

Some estimates have predicted that 90 per cent of the world’s corals could be dead by 2050.

The authors of the new study concluded that corals will continue to degrade until climate change stabilises. This will not only radically change reef ecosystems, but will harm the hundreds of millions of people – mainly in developing countries – who rely on coral reefs for their livelihoods.

“The Great Barrier Reef is certainly threatened by climate change, but it is not doomed if we deal very quickly with greenhouse gas emissions,” said Professor Hughes.

“Our study shows that coral reefs are already shifting radically in response to unprecedented heatwaves.”