Dead Reefs Can Come Back To Life, Study Says

Coral reefs may be able to recover from disaster, according to a study that provides a bit of reassurance about the future of these endangered ecosystems.

Coral reefs around the world are at risk as the ocean's temperature continues to rise. Those trends could kill not only coral but also the fish and other species that depend on the reefs. Those reefs are important for people as well.

'Shocking' Reef History

The study focused on beautiful coral reefs off the Pacific coast of Panama. They are seemingly a permanent feature of that coastline, but it turns out they have had a troubled history. Professor Richard Aronson at the Florida Institute of Technology and his colleagues discovered that by taking a core sample of the reef, just as a tree expert takes a sample of tree rings.

Fish swim by a colorful variety of coral near Indonesia's Komodo island.

(

Romeo Gacad

/

AFP/Getty Images

)

"We jammed 17-foot-long irrigation pipes down into the reef and pulled out a history, a section of the reef, that told us what the ups and downs of the reef had been," Aronson says.

It turns out that this 6,000-year-old reef hadn't simply been growing steadily throughout its history. In fact, the reef had actually died off for quite some time.

"These reefs were shut down for 2,500 years," Aronson says, "and the reefs have only been living for 6,000 years, so that represents about 40 percent of their entire history. So that's really shocking."

Shifting Climates

Aronson, along with colleagues from more than a half-dozen research institutions, suspect that a natural climate shift was responsible for this terrible episode. During the 2,500 years in question, findings from other studies show, the ocean water cycled frequently from way-too-hot El Nino conditions to the other extreme, La Nina.

"It wasn't just hot temperatures from El Nino. It was also more and more extreme La Nina events, which bring cold water," Aronson says. And the reef didn't grow well in either extreme.

But then the climate shifted again, to be much more like it is today. El Ninos and La Ninas still appeared, but not with such devastating extremes. And when the climate changed, the reefs came back to life.

"It seemed to be fairly instantaneous," Aronson says. "About 2,000 years ago or so, some corals that are not the main reef-building corals started up, and then maybe 500 years later, around 1,500 years ago, the main coral started growing again very rapidly."

All the fish and other reef creatures, which had apparently sought refuge elsewhere in the Pacific, returned. And the reef became much like the lively place it is today.

A Sign Of Hope?

Of course, Aronson is interested in the history of these reefs because he fears for the future. Climate change is likely to bring more devastating heat to these reefs and threaten them once again. On the other hand, his study finds that these reefs are remarkably resilient.

"What [this study] tells me is that these reefs do have hope, and if we are able to get a handle on climate change, then we might be able to save coral reefs," Aronson says.

Of course, that hope depends on being able to arrest climate change, which is a tough task. John Ogden, a leading voice for reef conservation and an emeritus professor at the University of South Florida, says he doesn't take too much comfort from this new study.

"What we're facing in terms of climate change is unprecedented around the globe," Ogden says. "So we don't really know whether coral reefs are going to be able to recover from future disturbances" the way they recovered from the one documented in the new study.

Even if reefs can recover over a period of a few hundred years, that's not great news for the next few generations. They may well witness sickly, bleached-white corals off the shores of Panama and elsewhere, instead of the ecosystems filled with colorful fish that we see today.

Copyright 2023 NPR. To see more, visit https://www.npr.org.