Amid growing concerns that the Great Barrier Reef is reaching an irreversible environmental tipping point, there is hope that two parts of the natural wonder can survive even on a warming planet.
And there are recommendations to better protect both sections from pressures such as fishing and shipping.
New modeling shows that remote reefs in the eastern Torres Strait and Whitsundays could remain 1 degree Celsius cooler than their neighboring reefs until 2080, in a worst-case scenario where greenhouse gas emissions continue unabated.
The areas of climate refugia – habitats that are largely buffered from climate change and where populations of organisms can survive adverse conditions – were described in a study published today in Scientific progress.
Bleaching occurs when coral, a living organism, expels algae it needs to survive due to environmental pressures such as heat stress. (Supplied: Australian Institute of Marine Science)
The research was conducted by the Commonwealth Scientific and Industrial Research Organization (CSIRO), the Australian Institute of Marine Science and several Australian universities.
Lead author Chaojiao Sun, a physical oceanographer from CSIRO, said it is still unclear whether corals can actually survive in these cooler regions. unknown.
“I think the good news is that we have used this worst-case emissions scenario, which we no longer take into account thanks to global climate action,” Dr Sun said.
Even if the identified reefs didn’t survive into the 2080s, Dr. Sun said the research showed they could be the best place to protect corals over the next 20 to 30 years and could provide a focus for more research.
“We have identified these valuable regions that are worth protecting to give them the best chance to survive and replenish the other coral reefs.”
Where are these reefs and why are they cooler?
Both northern and southern climate refugia were found on the eastern edge of the Great Barrier Reef.
The northern zone extends along the outer shelf from the eastern Torres Strait to the ribbon reefs off Cape York.
The other major refugium is located east of Mackay in the Pompey and Swain reef complexes.
The Great Barrier Reef has experienced mass bleaching several times over the past two decades (Delivered: scientific progress)
Both sites were less affected or escaped coral bleaching during the six mass bleaching events between 1998 and 2022.
Dr. Sun said the research team wanted to investigate why this was happening and model whether this would continue in the coming decades.
To do this, they conducted the first high-resolution regional ocean modeling of the Great Barrier Reef in a climate scenario known as Representative Concentration Pathway 8.5. This is sometimes called ‘business as usual’, where the countries of the world do nothing to reduce record levels of CO2 emissions.
Great Barrier Reef climate refugia compared to existing management zones. (Delivered: scientific progress)
The model took into account factors such as currents, tides and ocean topography and was able to simulate a phenomenon known as upwelling.
Upwelling is when warm surface water moves out of an area, allowing cooler, nutrient-rich water from deep to surface and replace it.
The main mechanism for upwelling in the Great Barrier Reef climatic refugia appeared to be the tide.
Coral bleaching at the Keppel Islands in the southern Great Barrier Reef in 2024. (Supplied: Renata Ferrari/Australian Institute of Marine Science)
Dr. Sun said the two climate refugia had densely packed reefs on the outer shelf, which explained why the upwelling was so effective at keeping temperatures an average of 1 degree cooler over a summer.
“When you let the tidal currents come through these very narrow reef channels… they have to squeeze through and become very strong, so they create a very powerful mixing of deep, cool water with the warm surface water,” she said.
“This doesn’t happen as consistently in the central Great Barrier Reef because the reefs are quite sparse… so the cool water stays near the bottom.”
According to the modelling, the upwelling will continue the northern and southern zones cooler than their neighboring reefs until 2080.
It is predicted that the northern and southern parts of the Great Barrier Reef will remain 1 degree Celsius cooler than surrounding reefs in a high emissions scenario by 2050. (Delivered: scientific progress)
Oceanographer Jennifer McWhorter of the US National Oceanic and Atmospheric Administration said the research was excellent, but the ecological and The biological response to warming was not well understood.
“Our understanding of the biological responses to warming in identified climate refugia areas of the Great Barrier Reef remains limited,” said Dr McWhorter.
That’s mainly because these areas are far offshore and difficult to study because of the deeper reef habitats, she said.
“For example, the range of variability in some of these (refugia) areas may be small, meaning that even a small increase in variability could endanger coral populations.”
Dr. McWhorter, who was not involved in the study, said future research should include biological and ecological modeling to better understand warming thresholds for specific species and habitats in offshore areas.
But she also said that despite the study’s findings, climate change remains a significant threat to the Great Barrier Reef.
Earlier this year, despite natural protection, southern climate refuges were hit by mass bleaching.
Map of Great Barrier Reef bleaching in 2024. (Supplied: Australian Institute of Marine Science)
When the researchers put data from 2024 into their model (which was not included in time for the published study), Dr Sun said the upwelling effect was still present, but other environmental factors had made it less effective that summer.
But she said the two climate refugia should still be prioritized for better protection because they are still cooler on average than other areas.
Changes in management proposed
Although much of the Great Barrier Reef falls within a marine park area, it has varying levels of protection some of it is still open to other uses, such as shipping and fishing.
The study found that 17 percent of the southern refugium was for general use activities such as fishing.
It was also found that large parts of the Northern Reef were outside the boundaries of the marine park and were instead managed by the Torres Strait Regional Authority.
Part of the coral reef near Lizard Island in December 2023/March 2024. (Supplied: George Roff/CSIRO)
Dr. McWhorter said future environmental management measures should focus on reducing stress on the reef created by humans, such as ship traffic and fishing.
Dr. Sun added that these areas could also be prioritized for interventions to help coral reefs recover, such as assisted colonization or coral evolution.
As intense marine heat waves become more common, Jessica Stella, acting chief scientist at the Great Barrier Reef Marine Park Authority, said a co-author of the study said identifying and protecting areas of climate refugia was crucial to improving the reef’s long-term prospects.
But ultimately, the best intervention for reefs, according to the research, is global climate action that would limit the frequency and severity of reefs’ exposure to heat stress.
Coral bleaching in the northern part of the Great Barrier Reef at Martin Reef in 2024. (Supplied: Veronique Mocellin/Australian Institute of Marine Science)
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