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Helpful Hurricanes

First-of-its-kind study links hurricanes to bleached coral revival

Coral
Time-series of bleached coral (Colpophyllia natans) at Coral Gardens, Florida Reef Tract. (A) Prebleaching (August 11, 2005). (B) Bleached (September 6, 2005). (C) Nearly recovered (November 9, 2005). (D) Recovered with normal pigmentation (March 2, 2006). (Photo courtesy of the Proceeding of the National Academy of Sciences)

VIRGINIA KEY, FL (July 2, 2007) — Hurricanes may be known for causing all sorts of destruction, but a new study out this week from scientists at the University of Miami Rosenstiel School of Marine and Atmospheric Science shows they may actually help bleached corals of varying degrees recover.

The research, published in the July 2007 issue of Proceedings of the National Academy of Sciences (PNAS), is the first study to highlight the potential benefit of hurricane-induced sea-surface cooling on coral bleaching. The magnitude and duration of sea temperature cooling coincident with the passage of hurricanes and tropical storms was assessed for five reef sites on the Florida Reef Tract from 1998 to 2005. Researchers found strong evidence that high wind speeds during hurricanes and tropical storms cooled surface waters enough to promote rapid and extensive recovery of bleached corals stressed by warming tropical waters in Florida.

“While it seems like an unlikely phenomenon at first, hurricanes are able to bring cooler waters to the surface, closer to where many corals reside and counter the now worldwide bleaching problem that may be a sign of global warming,” said Derek Manzello a marine biology and fisheries graduate student and a researcher for the National Oceanic and Atmospheric Administration (NOAA).

Data analyzed from the 2005 Atlantic hurricane season — the busiest season in recorded history —showed that the passage of hurricanes brought deeper, colder waters to the surface, alleviating some of the stress that Florida's coral reefs were experiencing from warm surface waters; allowing them to rapidly repopulate their symbiotic algae.

Coral bleaching is the loss of symbiotic algae (collectively termed zooxanthellae) from the coral animal. The photosynthetic zooxanthellae can provide up to 90-95 percent of the energy requirements of the coral host, thus bleaching is essentially the slow starvation of the coral. When the symbiotic algae are expelled by the coral host, the white calcium carbonate coral skeleton becomes visible through the animal tissues.

“The area affected by hurricane cooling is much larger than the narrow bands where damage actually occurs to reefs. Clearly, hurricane cooling isn't expected to completely negate the effects of climate change on coral reefs, but a well-timed hurricane or hurricanes has the potential to mitigate the negative ecological consequences associated with severe temperature disturbances,” said Marilyn Brandt a graduate assistant in the Rosenstiel School marine biology and fisheries division and the researcher whose previous work inspired Manzello's study.

Hurricane development is dependent on warm sea temperatures and often closely linked with widespread bleaching events. However, scientists have known that hurricanes reduce sea-surface temperatures upon passage. RSMAS professor, Peter Glynn, was the first to put forth the hypothesis that thermally stressed corals may benefit from cooling due to proximal hurricane passage. Until now, all the evidence for this phenomenon has been anecdotal or qualitative, or researchers have chosen to focus solely on the damaging effects of hurricanes on reef ecosystems. These results are the only known scenario where hurricane effects have been shown to benefit a stressed marine community.

Media Contact:
Ivy Kupec, Communications Director
Rosenstiel School of Marine & Atmospheric Science
305.421.4704 (o)
http://www.rsmas.miami.edu