Collapse of coral reefs could last thousands of years

— -- MELBOURNE, Fla. -- Coral reefs might be undergoing a total collapse that could last thousands of years, a situation made worse by man-made greenhouse gases, according to a Florida Tech study published in Science.

But reefs rebounded from previous climate extremes, so they can still be saved, the researchers say, as long as greenhouse-gas trends are reversed or stopped.

"It's one of these good news-bad news sort of scenarios," said co-author Richard Aronson, a biology professor at Florida Tech. "The hopeful news is that if we can get serious about controlling greenhouse gas emissions and controlling climate change, we have a good chance of saving reefs. But it has to be combined with management of local issues as well."

Coral reefs are crucial nurseries for fish and other marine life. Their demise could collapse global fisheries that support the food web, including humans. Mass coral die-off also could render extinct yet-to-be-discovered biological substances that hold cures for human diseases.

Natural global climatic swings stalled reef growth in the eastern Pacific Ocean for 2,500 years, the researchers found. The reef "hiatus," which began 4,000 years ago and lasted until about 1,500 years ago, corresponds to a period of extremes in the climate pattern that drives warm and cool cycles in the tropical Pacific. Plausible climate predictions for the next century are similar to those during that hiatus period, the study says.

Doctoral student Lauren Toth and Aronson, her adviser at Florida Tech, led the study, which included several other researchers and was supported by the Smithsonian Institution and the National Science Foundation.

The researchers examined how climate change influenced tropical reefs in the eastern Pacific.

They drove 17-foot, small-bore aluminum pipes deep into the ancient, skeletal foundations of coral reefs along the Pacific coast of Panama, extracting cross-sections of reefs.

From those coral cores, they reconstructed the reef's history over the past 6,000 years.

"We were shocked to find that 2,500 years of reef growth were missing from the frameworks," Toth said in a release. "That gap represents the collapse of reef ecosystems for 40 percent of their total history."

When they examined Pacific reef records from other studies, the researchers noticed the same gap in reefs as far away as Japan and Australia.

The timing of the stalled reef growth corresponds to a period of wild swings in the El Nio-Southern Oscillation, which drives El Nio and it's opposite cycle, La Nia, every several years.

El Nio is a pattern of warmer than usual water near the equator in the Pacific, while La Nia is its counterpart of cooler water.

Either extreme in water temperatures can slow or stop coral growth.

"Coral reefs are resilient ecosystems," Toth noted. "For Pacific reefs to have collapsed for such a long time and over such a large geographic scale, they must have experienced a major climatic disturbance.

In the eastern Pacific, at least, global warming predictions for the next 100 years echo climate patterns that collapsed coral reefs 4,000 years ago, the researchers said.

"Climate change could again destroy coral-reef ecosystems, but this time the root cause would be the human assault on the environment, and the collapse could be longer-lasting," Aronson said.

He says local issues such as pollution and overfishing are major factors destroying reefs but are "trumped" by global warming.

Recent El Nio and La Nia events have devastated tropical reefs. And if those two climate patterns continue to be made more extreme or mimicked by global warming, reefs could collapse again.

"But if Pacific reefs were able to recover after a millennial-scale hiatus in coral growth, and if current trends in CO2 emissions can be stopped or reversed, reefs of the future might also prove resilient," the authors wrote.

"This is not the time to give up and say it's all over," Aronson said.