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Two-thirds of the Great Barrier Reefs sees the largest amount of cover in 36 years, new report says.

Two-thirds of Australia’s Great Barrier Reef showed the largest amount of coral cover in 36 years, according to an official long-term monitoring programme but the reef remains vulnerable to increasingly frequent mass bleaching.

The recovery in the central and northern stretches of the United Nations Educational, Scientific and Cultural Organization or UNESCO world heritage-listed reef contrasted with the southern region, where there was a loss of coral cover due to crown-of-thorns starfish outbreaks, the Australian Institute of Marine Sciences (AIMS) said in its annual report on Thursday.

“What we’re seeing is that the Great Barrier Reef is still a resilient system. It still maintains that ability to recover from disturbances,” AIMS monitoring programme leader Mike Emslie told the Reuters news agency.

“But the worrying thing is that the frequency of these disturbance events are increasing, particularly the mass coral bleaching events,” he said.

Scientists, however, warned the reef was still exposed to ocean heating.

“While the coral cover is similar to what it was in the 1980s, people should not believe in any way that that means conditions on the reef are the same as they were in the 1980s,” Paul Hardisty, the CEO of the Australian Institute of Marine Science, told Al Jazeera.

“Nothing could be further from the truth. And the reason is because the reef is now subject in any given year to potentially devastating bleaching events caused not by solar radiation specifically, but by warming oceans and ocean heatwaves driven by climate change,” he said.

The publication of the report comes as UNESCO considers whether to list the Great Barrier Reef as “in danger”, following a visit by UNESCO experts in March.

The World Heritage Committee meeting where the fate of the reef was on the agenda was due to be held in Russia in June but was postponed.

In a key measure of reef health, AIMS defines hard coral cover of more than 30 percent as high value, based on its long-term surveys of the reef.

On the northern region, average hard coral cover grew to 36 percent in 2022 from a low of 13 percent in 2017, while on the central region hard coral cover increased to 33 percent from a low of 12 percent in 2019 – the highest levels recorded for both regions since the institute began monitoring the reef in 1985.

In the southern region, however, which generally has higher hard coral cover than the other two regions, cover fell to 34 percent in 2022 from 38 percent a year earlier.

The recovery comes after the fourth mass bleaching in seven years and the first during a La Nina event, which typically brings cooler temperatures. While extensive, the institute said, the bleaching in 2020 and 2022 was not as damaging as in 2016 and 2017.

On the downside, the growth in cover has been driven by Acropora corals, which AIMS said are particularly vulnerable to wave damage, heat stress and crown-of-thorns starfish.

“We’re really in uncharted waters when it comes to the effects of the bleaching and what it means moving forward. But as of today, it’s still a fantastic place,” Emslie said.