Scubaism

By mixing up cool deep layers of the ocean, a distant hurricane reduces sea-surface temperatures by several degrees—enough to help heat-stressed corals survive bleaching.

Bleaching occurs when sea temperatures warm, even slightly. This causes corals to eject their symbiotic, food-producing algae known as zooxanthellae (zoo-zan-thell-ay), leaving behind only the transparent coral tissue and bone white skeletons.

“It is well known that hurricanes can be catastrophic for reefs,” said study co-author Derek Manzello, a marine biologist from the Cooperative Institute of Marine and Atmospheric Studies in Miami, Florida. “[But] our results show that in [the study’s Florida test area] hurricanes may actually have been beneficial,” he said.

The research team used temperature data from across Florida’s reef tract, which arcs from just south of Miami to beyond Key West (Florida map) to show that winds whipped up by a hurricane can cool an 800 kilometer-wide (497 mile-wide) swath of water by an average of 1.5 degrees Celsius (2.7 degrees Fahrenheit) for ten days.

“Our underwater surveys showed that bleached corals in Florida immediately responded to the cooler water,” Manzello said. By November the reefs had almost completely recovered.

Hurricane cooling won’t completely nullify the dire prognosis for coral reefs under climate change, Manzello added. “Nonetheless, a well-timed hurricane has the potential to [lessen] the negative effects of increased temperatures.”

Manzello says that if climate change does bring more intense hurricanes, it is likely to be a double-edged sword: stronger hurricanes tend to be larger and so would cool a larger area. But their sheer force tends to destroy coral reefs.