NOAA 2002-013
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Warning Prompts Australian Scientists to Study Barrier Reefs for Coral Bleaching

Early warning data from NOAA polar satellites helped Australian researchers confirm the onset of widespread coral bleaching on reefs in the Great Barrier chain, the Commerce Department's National Oceanic and Atmospheric Administration said today. A team of scientists from the Australian Institute of Marine Science recently surveyed five reefs at distances from five to 130 km off the coast.

The survey was prompted by NOAA satellite images and AIMS-Great Barrier Reef Marine Park Authority instruments showing a vast section of the Coral Sea and Great Barrier Reef where temperatures are much higher than normal due to hot, clear summer conditions.

"Satellite data have been showing water temperatures to be running nearly 1 degree Celsius above what is customary for their summer over much of the Great Barrier Reef," said Dr. Al Strong, an oceanographer with NOAA's National Environmental Satellite, Data and Information Service. "We have not seen levels this elevated since 1998. The critical time appears to be over the next 30-40 days."

Using data from NOAA's polar-orbiting satellites, Strong produces sea-surface temperature charts and "Hot Spot" charts, which show areas of unusually warm ocean temperatures – where coral bleaching is likely. He provides this data to scientists around the world.

On Myrmidon Reef, the outermost reef where AIMS maintains one of its six automatic weather stations, the researchers found corals living on reef slopes were healthy and normal in color. Those on top, however, were bleached but otherwise apparently healthy.

"We expect corals will start to die if conditions don't moderate soon," said Dr. Terry Done of AIMS. "The mixing effect of a cyclone would do that best, but even normal wet-season clouds may be sufficient. We are still only learning about this phenomenon."

Two reefs about 70 km off the coast showed different responses. Rib Reef, like Myrmidon, was bleached on top but normal down the slopes, while John Brewer Reef, about 25 km to the southeast, showed little sign of any bleaching.

"The reef-top of John Brewer appears to be a few centimeters deeper than that on Rib Reef, which may be a helpful factor during very low tides," Done said.

At Magnetic Island, in the silty, shallow waters just off of Townsville, the reefs there were showing more bleached, diseased and dying corals down the slope.

"The corals' response of bleaching to compensate for the combined stress of excess heat and light seems to have left them less able to cope with silt or to resist diseases," Done said.

Bleaching is a sign of severe stress to corals, partially caused by prolonged exposure to warmer-than-usual water temperature. When water becomes too warm, corals expel the plant-like organisms that provide their color. Lacking these colorful organisms, corals appear white or "bleached." Since the organisms also supply nutrients, their loss can cause corals to starve and die.

NOAA Satellite Service is the nation's primary source of space-based meteorological and climate data. NOAA Satellite Service operates the nation's environmental satellites, which are used for weather forecasting, climate monitoring, and other environmental applications such as fire detection, ozone monitoring, and sea surface temperature measurements. NOAA Satellite Service also operates three data centers, which house global data bases in climatology, oceanography, solid-earth geophysics, marine geology and geophysics, solar-terrestrial physics, and paleoclimatology.

To learn more about NOAA Satellite Service, please visit

For additional information on Australian reef bleaching, please contact Done by phone: 07 4753 4344 or email:

For NOAA's Sea Surface Temperature Anomaly charts and HotSpot charts, visit: