Deeper parts of the threatened Great Barrier Reef are protected against climate change, a new study has found—but they won’t be for long.
If climate change continues, researchers from the universities of Exeter, U.K., and Queensland found that this protective barrier will be lost. Their findings are published in a Proceedings of the National Academy of Sciences study.
Australia’s Great Barrier Reef is highly important to the ecosystem and the local economy but it is under threat from bleaching. Bleaching occurs when corals turn white as a result of environmental pressures. In this state, the corals become highly vulnerable, meaning they are more likely to die. And when they die, they rarely grow back. Bleaching is mainly caused by higher than usual temperatures, which are increasing due to climate change. Mass bleaching events have occurred in the Great Barrier Reef for five out of the last eight years, the new study reports.
“The Great Barrier Reef has been experiencing recurrent widespread mass coral bleaching events, with one of the largest mortality events occurring as we speak. Therefore, this situation is extremely worrying,” Jennifer McWhorter, who led the research during a QUEX PhD studentship at the universities of Exeter and Queensland, told Newsweek.
The new study looked at the changing temperatures and how corals are reacting. They found that a separation between the warm surface waters, and cooler deeper waters, acts as a saving grace for many reefs that live further from the surface. However, if the global climate continues to warm, above 3°C pre-industrial levels, this cooling barrier could disappear.
They also found that bottom temperatures of the reef could increase by 1.2 to 1.7°C under higher emissions by 2050 to 2060.
The warmer the climate, the greater the risk of cooler and warmer waters mixing, exposing these reefs to the high temperatures, the study reports. And this does not just apply to the Great Barrier Reef. The researchers say this could be seen on other reefs worldwide.
“The finds were sensible as we would expect more ecosystems to be impacted under increased warming. Also, the concept of thermal stratification providing cooler temperatures at depth is not new, it just hasn’t been explored in the context of climate projections over the reef,” McWhorter said.
If temperatures warm by 3°C, the researchers found that the Great Barrier Reef could surpass 30°C. This has already been established as an important threshold for corals as this is the temperature bleaching occurs, the study reported.
McWhorter, who now works at NOAA’s Atlantic Oceanographic & Meteorological Laboratory, noted in a statement that some shallow-water coral species are not found in deeper areas. This means that mesophotic reefs “can’t provide refuges for them as shallow reefs are degraded.”
“And, as our study shows, mesophotic corals are themselves threatened if global warming continues,” she said.
“The number one thing that needs to be done to help the reef is for the global community to reduce carbon emissions. We can also manage other human-induced stressors on the reef better, such as reducing run-off pollution and limiting fishing activity,” the researcher told Newsweek.
Researchers need to understand coral reefs better in order to protect them, Paul Halloran, from Exeter’s Global Systems Institute, who also worked on the study, said in a statement. This is because they face multiple threats, he said, and some of these aren’t related to climate change.
“Our study focused on just the Great Barrier Reef. We need to explore this globally and using improved models to be able to provide detailed guidance to reef managers, and critically, we need to know how and under what conditions sea floor heatwaves lead to mortality on these deeper coral reefs,” Halloran told Newsweek.
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