Imma Perfetto
Cosmos science journalist
The deadly impact of climate change bringing more intense marine heatwaves and cyclones to the Great Barrier Reef has been revealed by initial results from the Australian Institute of Marine Sciences’ (AIMS) Long-Term Monitoring Program (LTMP).
The in-water surveys found that coral cover has declined between 11% in some places to as much as 72% in other sites, compared to pre-summer levels on 12 of 19 reefs surveyed so far.
The latest results from AIMS’ LTMP are concerning, but not surprising, Biodiversity Council member Professor Graeme Cumming, from the University of Western Australia Oceans Institute, told Cosmos.
“They show exactly what most coral reef scientists would expect. Ocean heating has caused the widespread mortality of many corals,” says Cumming.
“The weedy, fast-growing coral species that were responsible for the relatively rapid increases in total coral cover pre-bleaching have been hit the hardest.”
The reefs surveyed from August to October 2024 in the Great Barrier Reef (GBR) Marine Park are between Lizard Island and Cardwell in Queensland.
According to Dr Mike Emslie, leader of AIMS’ LTMP, all the reefs recently surveyed in this region were subjected to levels of climate change-driven heat stress that cause bleaching, in February and March 2024.
“Tropical Cyclones Jasper and Kirrily also exposed many to wave heights likely to cause damage to corals, generally greater than four metres,” says Emslie.
More than a third of hard coral cover was lost across the Cooktown-Lizard Island sector in its largest annual decline in 39-years of AIMS’ monitoring. The inner and mid-shelf reefs bore the brunt of the impacts from bleaching, with one inner shelf reef losing almost 3/4 of its pre-summer hard coral cover.
Coral cover declined by just over a third across the 5 reefs surveyed to date in the Cairns sector. Evidence of this damage was highest at Mackay Reef due to a combination of freshwater inundation, cyclonic wave damage and coral bleaching.
“More detailed analysis of the survey data will presumably provide more information about the new composition of the community of corals on the surveyed reefs,” says Cumming.
A full assessment of the impact on coral cover across the GBR Marine Park will be available in mid-2025.
“Of particular interest here will be the extent to which larger, older corals are being lost. These corals are critical for regenerating coral reefs because they produce many more offspring than the younger, smaller corals,” says Cumming.
Coral cover was largely unchanged on 3 reefs in the Innisfail sector, which saw lower heat stress from the marine heatwaves and less intense impacts from cyclones Jasper and Kirrily.
“Overall, it is encouraging that some reefs have not been hit as hard by recent bleaching events,” says Cumming.
“However, past experience shows that there is little predictability to the heating pattern, and it is possible that reefs that have escaped this bleaching event may bleach the next time water temperatures escalate.”
The Reef’s resilience is being severely tested, says AIMS acting research program director, Dr Manuel Gonzalez Rivero.
“These initial results show the vulnerability of the Reef to bleaching events, which are increasing in frequency, footprint and intensity under climate change,” says Gonzalez Rivero.
“The 2024 mass bleaching event on the Reef, its fifth since 2016, forms part of the fourth global bleaching event impacting both the northern and southern hemispheres of the Atlantic, Pacific and Indian Oceans during 2023 and 2024, documented in more than 60 countries and territories worldwide.”
Tropical cyclones are also expected to intensify with increasing global warming, according to the IPCC Sixth Assessment Report. The Australian Bureau of Meteorology forecasts 4 tropical cyclones for Australia’s Eastern region in the 2024–25 season.
Cumming says the Australian government is not doing enough to save the GBR.
“If they were serious about saving the reef, they would be doing everything they possibly could to reduce carbon dioxide emissions and maintain clean water in the GBR,” says Cumming.
“That would mean speeding up the transition to renewable energy and shutting down coal mines and oil and gas rigs – not approving new ones.
“Some additional measures that would help the reef would be to increase funding to limit harmful agricultural runoff into the waters of the GBR, reduce deforestation in the Daintree, stop coal-bearing ships from crossing the reef, reduce dredging programs that negatively impact water quality, and reduce commercial fishing activity within the marine park.”
Biodiversity Councillor Stan Lui, a Torres Strait Islander from Erub (Darnley Island) who has worked in senior roles in fisheries and natural resources management for state and federal governments and on national and international advisory boards, told Cosmos the recent coral bleaching events on the GBR signifies a dire threat not only to its vast biodiversity but also profoundly impacts the cultural and economic foundations of Aboriginal and Torres Strait Islander peoples.
“These communities, whose identities are deeply woven into the fabric of their Sea Country, are witnessing the degradation of essential cultural practices, sacred sites, and centuries-old knowledge,” says Lui.
“Bleaching events undermine important fisheries, pivotal to their ways of life and livelihoods, by diminishing fish populations and degrading marine habitats critical for cultural, commercial, and recreational purposes.
“This crisis underscores the urgent need for global cooperation to mitigate climate change and integrate Indigenous knowledge into conservation strategies, ensuring the reef’s preservation as both a biodiversity haven and a cultural treasure.”
The Ultramarine project – focussing on research and innovation in our marine environments – is supported by Minderoo Foundation.