Eastern Pacific Coral Reefs Adapting to Warmer Waters, Study Finds

The Uva Island Reef near the Pacific Coast of Panama.

The Uva Island Reef near the Pacific Coast of Panama. C.M. Eakin and T.B. Smith

Some corals in the eastern Pacific are adapting to a warmer world by hosting more heat-tolerant algae, according to new research that offers hope for the world’s embattled reefs.

The UN Intergovernmental Panel on Climate Change projects that at just 2 degrees C of warming, 99 percent of corals would be lost. However, the new study “shows that there are some unusual reefs that may be able to survive for several decades as a result of their ability to shuffle symbionts,” Andrew Baker, a marine biologist at the University of Miami and coauthor of the research, said in a statement.

“While we don’t think that most reefs will be able to survive in this way, it does suggest that vestiges of our current reefs may persist for longer than we previously thought, although potentially with many fewer species,” Baker said.

The algae that live in coral tissue supply their hosts with the nutrients they need to survive. Algae also give corals their vibrant color. When waters grow too warm, corals eject their algae and turn white, a phenomenon known as coral bleaching that leaves corals at greater risk disease and death. The new study finds that corals in Panama have adopted more heat-tolerant algae through a process of natural selection.

For the research, scientists tracked how reefs off Panama’s Pacific coast fared across three ocean heat waves — from 1982 to 1983, 1997 to 1998, and 2015 to 2016 — each of which struck during the Pacific’s warmer El Niño phase. While the 1982 heat wave decimated reefs, reducing coral cover by 85 percent, the 1997 and 2015 heat waves inflicted far less damage.

Scientists found that after heat waves, the heat-tolerant alga Durusdinium glynnii becomes more common, allowing corals to better withstand warm waters. Corals that host Durusdinium glynnii also grow more abundant. Scientists project that reefs bearing this heat-tolerant alga will be better-equipped to handle the more severe ocean heat waves predicted for later this century. The findings were published in the Proceedings of the National Academy of Sciences.

“Our results suggest that some reefs in the eastern tropical Pacific, which includes the Pacific coasts of Panama, Costa Rica, Mexico, and Colombia, might be able to maintain high coral cover through the 2060s,” Ana Palacio-Castro, a marine biologist with NOAA and lead author of the study, said in a statement. “However, while this may be seen as good news for these reefs, their survival may not continue past that date unless we reduce global greenhouse gas emissions and curtail global warming on a larger scale.”


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