Florida Cold Snap Devastated Coral Reefs

A school of glassy sweepers swims through elkhorn coral in this photo taken in the Florida Keys. CREDIT: Jeff Anderson, NOAA National Marine Sanctuaries View full size image

A 2010 cold snap in Florida caused widespread coral death in the reefs along the state's coast, a new study finds. In fact, the mortality rates from the cold were higher than in any other event on record.

"It was a major setback," said study researcher Diego Lirman, a professor of marine and atmospheric science at the University of Miami. "Centuries-old coral colonies were lost in a matter of days."

Winter temperatures in Florida that year hit record-breaking lows, driven down by cold air plunging southward from the Arctic. News organizations reported that Florida's tropical creatures struggled in the cold, including stubborn invasive species such as Burmese pythons and green iguanas.

Offshore, times were tough as well, researchers reported online Aug. 10, 2011, in the open-access journal PLoS Biology. The coral death rate shot up to 11.5 percent, compared with 0.5 percent in the previous five summers. The death rate dwarfs that of the summer of 2005, when Florida corals suffered high water temperatures and "bleached," the study found. Bleaching occurs when coral become stressed and expel the algae that help keep them alive. A few weeks of bleaching kills coral.

In some coral species, the researchers found, mortality rates hit 40 percent in the winter of 2010. Corals that had proved resilient to hotter-than-usual waters suffered when ocean temperatures dropped to 51 degrees Fahrenheit (11 degrees Celsius) in early January 2010.

"This was undoubtedly the single worst event on record for Florida corals," Lirman said in a statement.

Florida corals are vulnerable, because they're in the northernmost reaches of their range. Pollution, coastal development, overfishing and disease also strain coral reefs, which is within human control, Lirman said.

"We can't protect corals from such an extreme event," Lirman said of the 2010 winter. "But we can mitigate other stresses to help them recover."

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