The satellites - Terra and Aqua - are equipped with an instrument called the Moderate Resolution Imaging Spectroradiometer, or MODIS, which supplies near-real-time sea surface temperature and ocean color data that can provide rapid insight into the impact coral bleaching can have on global ecology.

"Australia's Great Barrier Reef is the largest and most complex system of reefs in the world, and like so many of the coral reefs in the world's oceans, it's in trouble," said oceanographer Gene Carl Feldman of NASA's Goddard Space Flight Center.

The reef is a massive marine habitat system actually comprising 2,900 separate reefs spanning more than 600 islands. Though coral reefs exist around the globe, researchers consider the Great Barrier Reef to be the center of the world's marine biodiversity, playing a critical role in human welfare, climate and economics. Coral reefs are multi-million dollar recreational destinations, and the Great Barrier Reef is an important part of Australia's economy.

Corals are much more than just a vibrantly colored backdrop to many divers' underwater adventures. Unknown to many, coral reefs are also critical to the marine ecosystem, serving as habitat and nursery grounds for fisheries, and providing coastline protection from severe storms by dampening wave action. On Australia's Great Barrier Reef, these gems of nature with their bursts of color have recently bleached, turning a stark white.

Bleaching occurs when warmer than tolerable temperatures force corals to cast out the tiny algae that help the coral thrive and give them their color. Without these algae, the corals turn white and eventually die, if the condition persists for too long.

"Coral, which can only live within a very narrow range of environmental conditions, are extremely sensitive to small shifts in the environment," Feldman said. "Like the 'canary in the coalmine,' coral can provide an early warning of potentially dangerous things to come."

NASA scientists have developed a free, Internet-based data distribution system that enables researchers around the globe to customize requests and receive the data captured by MODIS aboard Terra and Aqua, generally within three hours after the satellites pass over the particular region of interest.

Scarla Weeks of the University of Queensland, Australia, and colleagues are using the data to observe changes in sea surface temperature and ocean primary productivity along the reef and surrounding waters. Recent dramatic ocean-temperature increases are causing a rift in the mutually dependent relationship between corals and the algae that live within their bodies.

"The Great Barrier Reef is an icon, and we want to know what we can do to save it," Weeks said. "We would not be able to do this kind of broad-reaching work without NASA. With this satellite data delivery service we're able observe and understand what's happening in the ocean in ways we've never been able to before."

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