Palmyra reef
The Palmyra coral reef. Photo by Jennifer E. Smith

A 10-year study of a remote coral reef in the central Pacific Ocean by a team from Scripps Institution of Oceanography found that reefs can recover from bleaching due to higher water temperatures.

The researchers, who took over 1,500 photos underwater to analyze the changes over time, said the study shows the value of looking at long-term trends amid climate change.

The team from marine ecologist Jennifer E. Smith’s laboratory monitored Palmyra Atoll, which is located 805 miles south of Hawaii and is not permanently inhabited. It is described as a natural laboratory for monitoring how ecosystems change over time in response to climate warming.

“One year after each bleaching event, we did see signs of coral decline at some of the sites, but within two years this was restored,” said Adi Khen, a Scripps Oceanography Ph.D. candidate and lead author of the study.

“During the warming event that occurred in 2015, we saw that up to 90% of the corals on Palmyra bleached, but in the year following we saw less than 10% mortality,” Smith reported.

“Measuring not just death and destruction but measuring recovery is really important,” she said. “Seeing the recovery is where we can learn what might help inform future management.”

The Palmyra dataset suggests that warm-water events by themselves may cause some decline in reef-building corals and calcifying algae. But the atoll’s clean, protected waters and intact ecosystems harbor a healthy population of fishes that may contribute to the resilience of Palmyra’s reefs.

Past bleaching events have spawned widespread gloom-and-doom news reports about the future of Australia’s Great Barrier Reef and more general predictions of coral reef extinction by 2050.

But Smith said data from Palmyra gives scientists hope and clues for how to protect the reefs. “To know that places like this are out there showing signs of resistance and resilience gives us hope and also shows us that there’s still a lot to learn about how these intact systems are functioning,” she said.

Khen, Smith and four co-authors published their results in the journal Coral Reefs.



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Ellen Bullock