Great Barrier Reef: Concerns over future as latest coral-bleaching event strikes

The GBR is facing a “stark” future with climate-change induced coral bleaching striking the natural wonder, a globally respected Townsville academic says.

A coral atoll near Lizard Island on the Great Barrier Reef about 270 kilometres north of Cairns. The GBR is teetering on the brink, suffering one of the most severe coral bleaching events on record. Picture: AFP

Australia is facing a “stark situation” over the future of the Great Barrier Reef with climate-change induced coral bleaching affecting the length and breadth of the natural wonder, a respected Townsville academic says.

James Cook Professor of Physical Sciences Scott Heron, recently appointed the UNESCO Chair on Climate Change Vulnerability of Natural and Cultural Heritage, said bleaching was occurring in North Queensland waters but was particularly “extreme” in southern and far northern stretches of the GBR.

Coral reefs around the world have entered a fourth global mass bleaching event triggered by rising ocean temperatures.

Prof Heron said Australia and the global community needed to reduce greenhouse gas emissions.

“We have seen with increasing greenhouse gas concentrations in the atmosphere, increased warming of our atmosphere as well as our oceans,” he said.

“All governments need to be undertaking urgent and significant actions to reduce our fossil fuel emissions and our fossil fuel reliance.”

Professor Scott Heron looking across the iSimangaliso Wetland Park, a World Heritage property in South Africa, during the Climate Vulnerability Index workshop. Picture: Jon Day

Prof Heron said the shift away from fossil fuels needed to “happen in a just way”.

“We have people who are currently relying on those industries for their livelihoods and so we need to help those people transition into new employment areas because at the moment we are putting at risk the people whose livelihoods depend on a healthy and vibrant Great Barrier Reef.”

2024 Great Barrier Reef aerial survey map showing prevalence of coral bleaching in shallow-water coral communities. The Reef Snapshot 2023−24, released today by the Reef Authority, Australian Institute of Marine Science (AIMS) and the CSIRO, confirms the cumulative impacts experienced across the Reef this summer have been higher than previous summers. Picture: AIMS and Commonwealth of Australia

Coral bleaching is a stress response to elevated water temperatures, causing corals to expel the symbiotic algae living within their tissues.

Prof Heron said that a bleached coral was still alive and could recover by regaining the algae if temperatures cooled but would die if high water temperatures persisted.

He said it was too early to predict mortality rates for the current mass-bleaching event but past events gave an indication, including in 2016.

“For example, it was an estimated 30 per cent mortality of shallow-water corals experienced mortality, and that was focused in the northern GBR,” he said.

“In 2017, an additional 20 per cent mortality was estimated for that event and that was focused more in the central (Townsville) GBR.”

Bleached Acropora coral with lemon damselfish photographed in the Turtle Group National Park in the far northern Great Barrier Reef. Picture: TropWATER-JCU

Prof Heron said it was expected that the latest event would also have a high mortality rate.

“That’s a fairly stark situation.”

He said coral-bleaching events were “only going to continue as warming continues as a result of climate change”.

“We will more frequently see the reef being impacted and sections of the reef in unprecedented ways, seeing mortality.”

Bleached Acros white staghorn coral photographed in the Turtle Group National Park in the far northern Great Barrier Reef. Picture: TropWATER-JCU

Prof Heron said that “in Australia, we have the opportunity to adapt”.

“That is not the same situation, or at least not to the same degree, for many of our Pacific neighbours who are facing … the issue of climate change impacting not only on their livelihoods but also on their lives,” he said.

“And so as a good member of the Pacific community, it is essential that we as Australians, both individually and governmentally, take a leadership role in supporting our nearest neighbours.”

John Brewer Reef off Townsville post cyclone in February 2024. Picture: Matt Curnock-CSRIO

The Reef Snapshot 2023−24, released on Wednesday by the Reef Authority, Australian Institute of Marine Science and the CSIRO, confirmed the 2023−24 summer had seen substantial climate-driven impacts across the GBR, with widespread coral bleaching, two cyclones and several severe flood events.

Coral Bleaching on the Central Great Barrier Reef in February, 2024. Picture: Veronique Mocellin-Australian Institute of Marine Science

It said aerial surveys were conducted over 1000 reefs spanning the GBR Marine Park and Torres Strait and that coral bleaching was found in 73 per cent of surveyed reefs within the Marine Park and 6 per cent in the Torres Strait.

“The Snapshot shows the highest levels of coral bleaching were found across the southern region and parts of the central and northern regions, where in some areas, corals were exposed to record levels of heat stress,” the reports says.

“Parts of the central and northern regions also experienced the highest levels of coral bleaching,”

The Reef Authority’s chief scientist, Dr Roger Beeden, said climate change was “the greatest threat to the Great Barrier Reef, and coral reefs globally”.

“The Great Barrier Reef is an incredible ecosystem, and while it has shown its resilience time and time again, this summer has been particularly challenging.”

Originally published as Great Barrier Reef: Concerns over future as latest coral-bleaching event strikes