The Great Barrier Reef’s record coral coverage is good news, but the climate threat remains | Great Barrier Reef

Written by Javed Iqbal

That Great Barrier Reef is one of the planet’s natural jewels, stretching more than 2,300 km along Australia’s northeast.

But in addition to being a bucket-list favorite and a teeming mass of biodiversity across 3,000 individual reefs, the World Heritage-listed organism is at the coalface of the climate crisis.

But this week a report on the amount of coral across the reef showed the highest level in the 36 years of monitoring in the northern and central part.

But that doesn’t mean the crisis is over.

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Ecosystems are hit by multiple threats and disturbances, and for the reef they include invasions by voracious coral-eating starfish, pollution running off land and devastating cyclones.

The overwhelming threat is global warming, which has caused massive coral bleaching six times since 1998.

The Australian Institute of Marine Science (Aims), which runs the monitoring programme, examined 87 rev. The report counts hard corals — an important measure because their skeletons are what build structure for reefs.

The increase in coral cover was thanks to a fast-growing acropora coral, which is also the most susceptible to heat stress and is favored by coral-eating starfish.

Resilience versus Threats

Conditions in recent years have been relatively benign, with few cyclones, low numbers of starfish and two summers dominated by the La Niña weather pattern, which usually means cooler conditions.

But earlier this year was the first mass coral bleaching in a La Niña year – an event that shocked and surprised marine scientists who expect the cooler years will give corals a clear run to recover. Global warming now means that even La Niña years are not safe for corals. The inevitable arrival of a warmer El Niño phase has many extremely worried.

The first ever mass bleaching was in 1998, followed by events in 2002, 2016, 2017, 2020 and 2022. One study found only 2% of all reefs has escaped bleaching since 1998.

For the latest Aims monitoring report, around half of the reefs were visited before the summer bleaching. While bleaching was widespread, Aims said the heat probably wasn’t high enough to have killed many corals outright.

Depending on the severity of heat stress, corals can survive or die. If corals sit too long in warmer than normal water, they lose the algae that give them their color and most of their food.

This means coral starvation, so the events have sub-lethal effects on growth rate, ability to reproduce and susceptibility to disease.

Reef researchers talk about reef resilience – the ability to bounce back from disturbances.

“There is no doubt that this is good news,” says Dr. David Wachenfeld, Chief Scientist at the Great Barrier Reef Marine Park Authority.

“But we would be in deep trouble if the reef had already lost that resilience by 2022, at 1.1 C of global warming. We would have no chance of keeping the reef in a healthy state.

“According to last year [UN climate assessment], we will be at 1.5 C in warming in the next decade. It is an extremely confronting forecast. For a thermally sensitive ecosystem like the reef, that’s a lot, and it’s only about a decade away.”

Global warming of 1.5C is considered a bumper for reefs, after which the bleaching comes on too quickly for strong recovery.

“We’re on track to blow past 1.5C and get to 2.6C or 2.7C. So the resilience we’re seeing at 1.1C won’t continue,” says Wachenfeld.

Uncharted territory

Dr. Mike Emslie, who heads Aims monitoring, says the increase in coral cover was expected given the relatively benign conditions, but four bleaching events in seven years was uncharted territory.

“We’ve dodged a few bullets in the last few years, and while this recovery is great, the predictions are that the disruptions will get worse,” he says.

In some conservative media, the study has been used to make arguments that the reef is not threatened. “The naysayers can bury their heads in the sand all they want, but the frequency of disruption is skyrocketing,” says Emslie.

Wachenfeld points out that scientists have never said the reef is dead. “Scientists have rung an alarm bell, not a funeral dirge,” he says. “The notion that scientists have misled people is nonsense.”

He compares the reef’s resilience to a rubber band that can be stretched many times, but only so far before it breaks.

“It’s hard to predict when that will happen, but it’s kind of like that with the reef,” he says. “We have a finite amount of time to slow down and stop the warming. There’s no way this resilience can last forever.”

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Javed Iqbal

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