Coral reefs have taken hit after hit. A new study says some parts of them may still have a shot.
Researchers identified more than 64,000 square miles, about 166,000 square kilometres, of coral reefs across 71 countries and 100 territories with the potential to survive warming oceans, according to findings presented on June 16 at the Our Ocean Conference in Mombasa, Kenya. The study is available on the pre-print server EcoEvoRxiv and is undergoing peer review for publication.
“Coral reefs are often framed as ecosystems beyond saving,” said study co-author Emily Darling, director of coral conservation at the Wildlife Conservation Society, at the conference, per Anand Ram at Canadian Broadcasting Corporation News. “This research shows otherwise.”
Corals are made of tiny animals called polyps. Hard corals make rigid skeletons of calcium carbonate to protect their soft interiors, and collections of these hard corals are considered coral reefs.
Coral reefs span just 1 percent of the seafloor, but they are estimated to support a quarter of marine life. They are also among the most vulnerable ecosystems, threatened by pollution, overfishing and rising ocean temperatures that make bleaching events more frequent.
Bleaching happens when water that is too warm causes coral to expel the algae living in its tissues. That removes its main food source and causes it to turn white. Bleached coral is still alive in the short term, but it is stressed and can die if conditions persist.
Previous research has identified three types of climate-change safe havens, or refugia, for corals. Some areas have protections linked to physical characteristics of climate stressors such as heat, called avoidance refugia. Researchers have identified that type most often. There are also resistance refugia, where corals are better able to tolerate heat stress, and recovery refugia, where reefs can quickly bounce back after exposure to heat.
Darling and her colleagues trained artificial intelligence to identify these refugia using about 45,000 coral reef observations collected since 1960. The model used 42 predictors, including ocean temperature, chemistry and human pressures, to estimate coral cover and community composition in 2020 and predict cover in 2050.
The researchers then fed two coral reef habitat maps into the model, which identified coral regions showing characteristics of climate resilience. About 61 percent of the area is in the coastal waters of five countries: Australia, the Bahamas, Cuba, Indonesia and the Philippines.
The study also identified potentially significant refugia in Belize, Nicaragua and the Turks and Caicos Islands, adding to the areas found in the 50 Reefs assessment published in 2018. That assessment was the first overview of coral reefs that could withstand climate change.
“This [new] study sharpens decades of work on reef resilience to climate change,” David Obura, a marine ecologist and chair of the Intergovernmental Platform on Biodiversity Ecosystem Services who was not involved in the new research, told Katharine Houreld at The New York Times. “It focuses attention on the critical question: Will climate refuges comprise 10 percent, 1 percent or even less of the former extent of coral reefs?”
The findings for the Turks and Caicos Islands stood out because there is a lack of long-term coral data there, Alizee Zimmermann, executive director of the Turks and Caicos Reef Fund, who was not involved in the research, told Teresa Tomassoni at Inside Climate News. She said she would like to see how the surveys used in the study were conducted.
Zimmermann also said nuance matters. “The narrative that Caribbean reefs are simply ‘dead’ is inaccurate and can be harmful to progress on reef restoration and protection initiatives in the region,” she tells the outlet. “However, it would be equally disingenuous to say that they are thriving.”
The study’s authors said they want the work to guide where countries invest conservation funding, especially small nations with limited resources. “Climate-resilient reefs are not spread evenly,” said study co-author Joseph Maina, an environmental scientist at Macquarie University in Australia, at the conference, reports CBC News. “And countries need to understand … those differences such that when they plan where future conservation investment should go, they consider this uneven distribution.”
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