It’s the world’s largest collection of coral reefs, spanning more than 1,430 miles down Australia’s eastern coastline.
But scientists warn that the Great Barrier Reef is inching closer to an irreversible ‘tipping point’ as it gets ‘repeatedly hammered’ by global warming.
Parts of the Reef have suffered the highest coral death on record, according to experts at the Australian Institute of Marine Science’s (AIMS).
The marine research centre – which began monitoring the world-famous reef in 1985 – surveyed 19 reefs along the famous region between August and October this year.
Over the period, 12 out of 19 suffered from a decline in ‘coral cover’ – the area on a reef that’s covered by live coral.
One reef suffered from 72 per cent coral mortality, largely due to to high temperatures caused by climate change, as well as two cyclones and flooding.
This year had already been confirmed as the fifth mass bleaching on the reef in the past eight years.
What’s more, this latest round of underwater surveys only looked at three of the Great Barrier Reef’s 11 sections or ‘sectors’ – so the overall picture may be even worse.
One of the major contributors to coral loss has been heat stress driven by climate change, said AIMS leader Dr Mike Emslie.
Exposure to ongoing heat, pollution and low tides can result in coral expelling its algae, which turns the coral from a vibrant colour to white, better known as ‘bleaching’.
If heat continues to affect the area, the algae won’t return and the coral is left to die.
‘The heat stress got so high in some areas that mortality is not a surprising outcome,’ Dr Emslie said.
Two cyclones and flooding between December 2023 and March 2024 have also affected the health of the coral.
Heavy rainfall can reduce salinity which corals need to survive, while large storm waves can result in heavy physical damage to coral reefs.
‘Tropical Cyclones Jasper and Kirrily also exposed many to wave heights likely to cause damage to corals, generally greater than four metres,’ Dr Emslie added.
Between August and October, AIMS surveys covered three geographical ‘sectors’ along the northeast – Cooktown-Lizard Island, Cairns and Innisfail.
Around a third of live coral was lost across the Cooktown-Lizard Island sector, which suffered the largest annual decline for this sector in 39 years of AIMS monitoring efforts.
In the Cairns sector, coral cover declined by around a third across all five of the sector’s reefs, while in the Innisfail sector, coral cover remained similar to pre summer levels across the four reefs surveyed.
In the Innisfail sector, the heat stress from the marine heatwave was lower, and the impacts from cyclones Jasper and Kirrily were less intense.
AIMS expects to survey another 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 the initial surveys confirmed his ‘worst fears’.
‘The Great Barrier Reef can bounce back but there are limits to its resilience,’ he said.
‘It can’t get repeatedly hammered like this. We are fast approaching a tipping point.’
Although only three sectors in the northernmost part of the reef have been surveyed, scientists fear the rest of it has suffered a similar fate.
Leck added the area surveyed was ‘relatively small’ and feared that when the full report is released next year ‘similar levels of mortality’ will be seen.
He said that it reinforced Australia’s need to commit to stronger emission reduction targets of at least 90 percent below 2005 levels by 2035 and move away from fossil fuels.
The country is one of the world’s largest gas and coal exporters and has only recently set targets to become carbon neutral.
In all, the Great Barrier Reef has seen five mass bleaching events – in 1998, 2002, 2016, 2017, 2020, 2022 and now in 2024.
Bleached corals are not dead, but are at a higher risk of dying, and these bleaching events become more common under climate change.
While some coral reefs are able to recover over time, others become dominated by seaweed.
Coral can survive bleaching if it receives nutrients soon enough, but if not, it can cause death within days, previous studies have shown.
