Whitney Isenhower looks at how researchers are turning to heat-tolerant corals to help save eroding coral reefs amid the climate crisis.
A version of this article was originally published by The Conversation (CC BY-ND 4.0)
Austin Bowden-Kerby, a pioneer in coral reef conservation, spends most of his days in the coral reef gardens of Fiji and the Pacific. He grows corals in marine greenhouses. Once they are healthy, you take them to offshore areas in the hope that they will multiply and grow.
“We’re looking at what Mother Nature would do on her own if she had 1,000 years to adapt,” said Bowden-Kerby, who developed the UNESCO-endorsed Reefs of Hope strategy. “We were going to do these kinds of things.”
Bowden-Kerby is one of the few scientists trying to save, replicate and reproduce heat-resistant corals before climate change wipes them out.
The United States National Oceanic and Atmospheric Administration said the world is facing the fourth global coral bleaching event. They found that global warming will affect about 85pc of the world’s coral reefs between 2023 and 2025.
Cleaning causes corals to lose their food source and, with it, their color. Most corals live in temperatures between 20 and 29C. But as ocean temperatures rise, it’s hard for many to make it.
But naturally occurring, heat resistant corals can survive in water up to 36C and higher. They are usually found in warm waters, such as parts of the Pacific Ocean and the Persian Gulf. These corals are becoming increasingly important as ocean temperatures rise. So scientists turned to them to help save the crumbling reefs.
Corals are heat resistant
Coral reefs are extremely diverse habitats, with around 6,000 coral species worldwide. Reefs are home to more than 4,000 species and 25pc of the world’s marine life. When healthy, corals feed fish that feed communities, protect coastlines from floods and storms and boost the economy through tourism.
However, heat waves have led to coral destruction and loss. When the water gets too warm, corals release algae from their tissues that give them color. That causes the corals to turn completely white.
Coral reefs and their ecosystems are also threatened by pollution, ocean acidification, coastal development and overfishing.
Christopher Cornwall, a lecturer in marine biology at Te Herenga Waka-Victoria University of Wellington in New Zealand, co-authored a recent review that found some reefs could survive if corals could withstand the heat.
He told me that there are many things to consider when conserving and reproducing corals: restoring heat-resistant corals where possible, doing so on a large enough scale and maintaining coral diversity. Restored corals must be able to survive, he added.
“We can’t just restore corals without heat-tolerant corals, because they will die the next time it gets too hot,” Cornwall said.
Evolution is assisted
“A lot of research now is about, can you increase returns and how do you do it effectively?” said Peter Mumby, a professor of coral reef ecology at the University of Queensland in Australia. “One of the key concerns is making sure those corals are able to tolerate as high a temperature as possible.”
Breeding heat-tolerant corals is a way to help evolution. Humans are intervening to accelerate natural processes to help corals respond quickly and recover from stressors, such as heat waves from climate change.
One recent study examining the potential success of assisted evolution interventions such as breeding and selection for traits found that these interventions can help corals tolerate heat waves, but require “very strong selection”.
Liam Lachs co-authored that study. Lachs is a postdoctoral research associate in the CoralAssist lab, a team of scientists led by James Guest at the University of Newcastle in the United Kingdom. Lachs specializes in coral reef ecosystems and researches the corals of Palau, a Pacific island nation where corals live in warm waters.
He told me the variability within and between coral reefs and coral species must be considered when building heat-resistant corals, making replication difficult. “Even within a single rock, there is a range of tolerance levels,” he said.
Algae and bacteria
Researchers at the Australian Institute of Marine Science (AIMS) discovered that certain algae (Durusdinium), which live on corals together and provide them with food for shelter and protection, can improve the heat tolerance of corals.
Madeleine van Oppen is a senior research scientist at AIMS. He co-authored a recent review on introducing beneficial bacteria to corals to improve heat tolerance.
Scientists are also investigating whether heat-tolerant corals should be planted across the ocean – from the Indo-Pacific region to the Caribbean – and not just in nearby waters.
Van Oppen said new businesses ultimately require more research, and the true test of success is when something developed in the lab works in the field. “Field testing, I would say, is the next big thing,” he said. “Finding that this intervention can develop tolerance on an ecological scale. Is it sustainable over time?”
AIMS researchers also discovered that heat tolerance can be transferred by breeding wild colonies of the same coral species. Coral species that can withstand heat include pocillopora and acropora.
If left unchecked, global warming is set to increase by more than 1.5C. Some evidence has shown that 70 to 90pc of tropical coral reefs could disappear even if global warming is limited to 1.5C.
Before the fourth event, the Earth has already experienced three coral bleaching events in the past few decades. An El Niño is expected this year, which will bring warmer ocean temperatures, like in 2024.
For all the scientists’ efforts to save coral reefs and ensure they are resistant to heat, nothing will keep corals healthy more than lowering global temperatures. “The more greenhouse gas emissions we get, the more likely there will be greenhouse reefs in the future,” said Cornwall.
Written by Whitney Isenhower
Whitney Isenhower is a freelance journalist and communications consultant specializing in health, climate and science. His work has appeared in Devex, Live Science and North Carolina Health News. He previously supported projects of the US Agency for International Development until 2025. She also completed a fellowship in journalism and health impact through the University of Toronto Dalla Lana School of Public Health.
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