It is the largest collection of coral reefs in the world and stretches for more than 1,430 miles along the east coast of Australia.
But scientists warn that the Great Barrier Reef is inching closer to an irreversible “tipping point” as it is “hit repeatedly” by global warming.
Parts of the reef have suffered the largest coral die-off ever recorded, according to experts from the Australian Institute of Marine Science (AIMS).
The marine research centre, which began monitoring the world-famous reef in 1985, surveyed 19 reefs across the famous region between August and October this year.
During the period, 12 of 19 suffered a decline in “coral cover” – the area of a reef covered by live coral.
One reef suffered 72 percent coral mortality, largely due to high temperatures caused by climate change, as well as two cyclones and floods.
This year had already been confirmed as the fifth mass bleaching on the reef in the last eight years.
What’s more, this latest round of underwater studies only looked at three of the 11 sections or “sectors” of the Great Barrier Reef, so the overall picture may be even worse.
AIMS surveyed 19 reefs in three geographic “sectors” across the northeast: Cooktown-Lizard Island, Cairns and Innisfail. During the period, 12 of 19 suffered a decline in “coral cover” – the area of a reef covered by live coral.
It is the largest collection of coral reefs in the world and stretches for more than 1,430 miles along the east coast of Australia. But scientists warn that the Great Barrier Reef is inching closer to an irreversible “tipping point.” Pictured is a coral community with live and dead hard corals in the Cairns sector.
Pictured, live branching corals in the Cooktown-Lizard sector surrounded by table corals that died due to a marine heatwave in early 2024.
One of the main contributors to coral loss has been heat stress caused by climate change, said AIMS leader Dr Mike Emslie.
Exposure to constant heat, pollution, and low tides can cause coral to expel its algae, turning the coral from a vibrant color to white, better known as “bleaching.”
If the heat continues to affect the area, the algae will not return and the coral will die.
“Heat stress became so high in some areas that mortality is not a surprising result,” Dr. Emslie said.
Two cyclones and floods between December 2023 and March 2024 have also affected coral health.
Heavy rainfall can reduce the salinity that corals need to survive, while large storm waves can cause serious physical damage to coral reefs.
“Tropical cyclones Jasper and Kirrily also exposed many people to wave heights likely to cause damage to corals, typically greater than four metres,” Dr Emslie added.
Between August and October, AIMS surveys covered three geographic “sectors” across the North East: Cooktown-Lizard Island, Cairns and Innisfail.
Coral cover has declined on 12 of 19 reefs studied between Lizard Island and Cardwell after a summer of disturbance.
The Reef has suffered heat stress as a result of climate change and recent cyclones. This year had already been confirmed as the fifth mass bleaching on the reef in the last eight years.
The Great Barrier Reef, a UNESCO World Heritage Site, contains the largest collection of coral reefs in the world, with 400 types of coral, 1,500 species of fish and 4,000 types of mollusks.
About a third of the live corals were lost across the Cooktown-Lizard Island sector, which suffered the lThe largest annual drop for this sector in 39 years of AIMS monitoring efforts.
In the Cairns sector, coral cover decreased by around a third on the five reefs in the sector, while in the Innisfail sector, coral cover remained similar to pre-summer levels on the four reefs studied.
In the Innisfail sector, thermal stress caused by the marine heatwave was lower and the impacts of cyclones Jasper and Kirrily were less intense.
AIMS expects to survey a further five to 10 reefs in the Cairns sector and four to five reefs in the Innisfail sector in the coming months.
Additional reefs may be surveyed in the Cooktown-Lizard Island sector later in the season, depending on weather conditions.
WWF-Australia’s head of oceans, Richard Leck, said initial studies confirmed his “worst fears”.
“The Great Barrier Reef can recover, but its resilience has limits,” he said.
‘You can’t hit repeatedly like this. “We are rapidly approaching a tipping point.”
Although only three sectors in the northernmost part of the reef have been studied, scientists fear that the rest have suffered a similar fate.
This underwater photograph taken on April 5, 2024 shows bleached and dead corals around Lizard Island on the Great Barrier Reef, 170 miles (270 km) north of the city of Cairns.
Bleached corals are not dead, but they are at higher risk of dying, and these bleaching events are becoming more common with climate change.
Leck added that the area studied was “relatively small” and he feared that when the full report is published next year “similar levels of mortality” will be seen.
He said this reinforced Australia’s need to commit to tougher emissions reduction targets of at least 90 per cent below 2005 levels by 2035 and move away from fossil fuels.
The country is one of the world’s largest exporters of gas and coal and has only recently set goals to become carbon neutral.
In total, the Great Barrier Reef has suffered five mass bleaching events: in 1998, 2002, 2016, 2017, 2020, 2022 and now in 2024.
Bleached corals are not dead, but they are at higher risk of dying, and these bleaching events are becoming more common with climate change.
While some coral reefs may recover over time, others become dominated by algae.
Coral can survive bleaching if it receives nutrients soon enough, but if not, it can cause death within days, previous studies have shown.