WASHINGTON (AP):

Corals stressed by warming conditions may benefit from the passage of a hurricane - as long as it doesn't slam right into them.

Bleaching of corals has been a growing problem in recent years with the loss of algae or reduction of pigment in the living corals that occurs when they are stressed by warming water.

Now, a team of researchers led by Derek P. Manzello of the United States National Oceanic and Atmospheric Administration (NOAA) reports that hurricanes mix the warm surface water and colder deep water enough to lower the temperature as much as five degrees Celsius.

The researchers studied damaged reefs in Florida and the Virgin Islands that suffered in a 2005 bleaching event. They report their findings in Tuesday's issue of Proceedings of the National Academy of Sciences.

Bleaching was similar in both regions, but following the passage of Hurricane Rita in September, the Florida corals began to recover, and recovery accelerated after Hurricane Wilma passed by in October. Bleaching continued in the Virgin Island corals, which had not been approached by the storms.

The researchers concluded that while a direct hit by a hurricane can damage corals, passage of a storm within 250 miles (400 kilometres) or so can mix and cool the water enough to benefit corals.

The research was funded by NOAA's Coral Reef Conservation Programme, the National Center for Coral Reef Research, the Project Aware Foundation, the U.S. Virgin Islands department of natural resources and NOAA's National Center for Coastal Ocean Science.