Record coral cover for Great Barrier Reef: Australian Institute of Marine Science

The reef has set a new record for hard coral cover over two-thirds of its 2300km length, an official long-term monitoring program shows.

A diver with the Australian Institute of Marine Science examines the reef. Source: Australian Institute of Marine Science

The Great Barrier Reef has set a new record for hard coral cover over two-thirds of its 2300km length, results of the Australian Institute of Marine Science official long-term monitoring program show.

The annual survey found coral cover in the northern and central zones of the Reef, stretching from Cape York to Mackay, had increased despite another episode of bleaching this year.

Coral cover in the southern section of the Reef which stretches from Mackay to Bundaberg had reduced slightly due to a continued outbreak of crown of thorns starfish, but coral cover was comparable to the northern and central regions at 34 per cent.

The AIMS long-term monitoring program has been going for 36 years and is the most rigorous and detailed survey of Reef health.

AIMS program leader Mike Emslie said the results were “good news” and showed that the Reef had “dodged a bullet” in bleaching this year.

“But the fact we have had four bleaching events in seven years is a major concern and highlights the impact of climate change here and now,” he said.

“We are in uncharted territory and still trying to understand what this means.”

Queensland scientist Peter Ridd said the results “should be a cause of national celebration”.

Dr Ridd said coral cover on the Reef as a whole was at record high levels.

“This brilliant result is proof that many science institutions have been misleading the public about the state of the Reef,” he said.

 

The full impact of this year’s bleaching will not be known until further monitoring is done but expectations are that mortality rates across the Reef will be low.

“The recovery seen this year occurred despite widespread bleaching in 2020 and again in 2022, showing bleaching events do not always lead to widespread mortality,” the report says.

“The 2022 bleaching event was less intense than the 2016, 2017 and even the 2020 events, and mortality is expected to be lower.

“However, the nonlethal effects of frequent bleaching events will take time to be fully understood.”

The significance of the latest AIMS results is that it shows the Great Barrier Reef has maintained its resilience and ability to bounce back from disturbances including bleaching and cyclones.

There are still concerns about the impact of consecutive bleaching events and what this means for the make-up of the Reef and factors other than the amount of hard coral cover.

Eighty-seven reefs were surveyed between August 2021 and May 2022, mainly on the mid and outer shelf.

Mike Emslie. Picture: Marie Roman

The recovery has been primarily driven by fast-growing branching and plate corals (Acropora species), which provide good habitat for fish and other reef animals but are vulnerable to disturbances such marine heatwaves, cyclones and crown-of-thorns starfish predation.

AIMS chief executive Paul Hardisty said the results in the north and central regions were a sign the Reef could still recover, but the loss of coral cover in the southern region showed how dynamic the Reef was.

“Every summer the Reef is at risk of temperature stress, bleaching and potentially mortality, and our understanding of how the ecosystem responds to that is still developing,” he said.

Great Barrier Reef Marine Park Authority chief scientist David Wachenfeld said the results showed that the Reef was still a resilient ecosystem, retaining its capacity to recover from disturbances, at the current level of global warming which is about 1.1C warmer than the pre-industrial temperature.

“Given the significant climate change-driven impacts we have already seen, our biggest concern is for the future, as temperatures increase, because the resilience of the Reef will not withstand future projected warming on current trajectories of greenhouse gas emissions,” he said.

The bleaching this year coincided with a visit by a World Heritage Committee monitoring mission to advice on whether or not the Great Barrier Reef should be inscribed on the World Heritage “in danger” list.

The 2022 World Heritage Committee meeting was scheduled to be held in Russia, and has been postponed.

Dr Emslie said he was sure the World Heritage Committee would take the results of the latest AIMS survey into consideration.

Dr Ridd said AIMS should be congratulated for their work over many decades.

“I estimate that in these surveys, AIMS has towed a diver behind a small boat a distance equivalent to around the world,” he said.

“This work has paid off as it demonstrates that the Reef cycles through periods of high and low coral cover.

“This is natural.

“It demonstrates that we should be far more optimistic about the fate of the Reef.”