Coral restoration throughout a protracted warmth wave provides new hope

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UNIVERSITY OF VICTORIA

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IMAGE: UVIC MARINE BIOLOGIST JULIA BAUM SAMPLING PLATYGYRA COLONIES ON KIRITIMATI (CHRISTMAS ISLAND), 2019. Show more CREDIT: CREDIT: KRISTINA TIETJEN.

Biologists at the University of Victoria found how some corals managed to survive a heat wave unprecedented in the world in an initial study that offers new hope for long-term survival of coral reefs in the face of climate change.

“The devastating effects of climate change on coral reefs are well known. Finding ways to improve coral survival from marine heat waves is critical if coral reefs are to withstand decades of climate change, ”says UV marine biologist Julia Baum, lead author of the study.

The study, published today in Nature Communications, presents the discoveries made by the international research team that tracked hundreds of coral colonies on reefs around Christmas Island (Kiritimati) during El Niño 2015-2016. The El Niño heat stress triggered the third global coral bleaching event, causing mass coral bleaching and mortality on reefs around the world. The epicenter was Christmas Island, where the heat wave lasted an unprecedented 10 months.

Globally, coral reef fisheries are valued at $ 6.8 billion annually and are a vital source of food and income for hundreds of millions of people in tropical island nations. In the run-up to the United Nations Decade for the Exploration of the Sea for Sustainable Development (2021-2030), global calls are being made to reverse the cycle of declining marine health.

“If we understand how some corals can survive prolonged heat waves, we can mitigate the effects of marine heat waves on coral reefs and gain time to limit greenhouse gas emissions,” says Danielle Claar, who led the study as a UV radiation PhD student and is now a postdoctoral fellow at the University of Washington.

Climate change is threatening the world’s coral reefs as corals are very sensitive to the temperature of their surrounding waters. During a heat wave, corals release the algae that live in their tissues and produce food for them, causing the coral to become completely white – a phenomenon known as coral bleaching. Prolonged bleaching often causes corals to die of starvation. If they can regain their food source within a few weeks, they can usually recover.

So far, coral recovery after bleaching has only been observed after the heat stress has subsided. As global climate models predict that heat waves will continue to increase in both frequency and duration, the ability of a coral to regain its food source during a prolonged heat wave is critical to its survival.

“Watching corals recover from bleaching while they’re still baking in hot water changes the game,” says Baum.

Baum adds that corals only exhibited this ability when they weren’t also exposed to other types of man-made stressors such as water pollution. So far, it was unclear whether local reef management could help improve corals’ chances of survival in the face of climate change. “We have found a glimmer of hope that protection from local stress factors can help corals,” says Baum.

“While this path to survival may not be open to all corals or in all conditions, it demonstrates an innovative survival strategy that conservationists could use to help coral survive,” adds Claar.

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The research was funded by the Canadian Science and Engineering Research Council, the US National Science Foundation, the David and Lucile Packard Foundation, the Pew Charitable Trusts Pew Fellows program for marine conservation, the Rufford Foundation, the Canadian Foundation for Innovation, and the Shedd Aquarium .

From EurekAlert!

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