A massive coral bleaching event in Southeast Asian reefs in the Indian and Pacific oceans is the worst coral die-off since 1998, and possibly the worst science has ever observed, says Andrew Baird of the ARC Center of Excellence for Coral Reef Studies at James Cook University.

Bleaching occurs when environmental factors stress the living organisms residing within coral reefs, causing them to either leave their reef structures or die. The reefs, which turn white, or are bleached, become unable to support the myriad biodiversity that rely on them for food or habitat.

The coral die-off is afflicting reefs in waters bounded by the Philippines, Sri Lanka, Burma, Thailand, Malaysia, Singapore and Indonesia. Included is the Coral Triangle, an area in the Pacific between Indonesia and the Solomon Islands that supports the greatest volume of marine biodiversity in the world, earning it the nickname the "Amazon rainforest" of the oceans. The Coral Triangle alone represents 5.7 million square kilometers of pelagic territory.

Throughout the region of the die-off, "around 80 percent of Acropora colonies and 50 percent of colonies from other species have died since the outbreak began in May this year," Baird said in a prepared release.

The cause of this massive bleaching event? According to a release from ARC, "a large pool of superhot [sic]" water...swept into the eastern Indian Ocean region several months ago, shocking the corals and causing them to shed the symbiotic algae that nourish them." The warmer-than-normal water started at the surface of the ocean, where temperatures peaked in May 2010 at levels 4 degrees Celsius above the long-term average for the area.

Baird blames climate change for putting the coral in hot water. "My colleagues and I have high confidence these successive ocean-warming episodes, which exceed the normal tolerance range of warm-water corals, are driven by human-induced global warming," he said. "They underline that the planet is already taking heavy hits from climate change—and will continue to do so unless we can reduce carbon emissions very quickly. They also show this is not just about warmer temperatures, it is also threatening the livelihoods of tens of millions of people, and potentially the stability of our region," he adds.

Baird says the affected colonies could shrink in size from 50 to 90 percent, devastating the biodiversity that depends on them as well as local fishing and tourism industries.

Photo: Reefs of Pulau Weh—before, during and after the bleaching event. (a) April 18, 2009; (b) May 31, 2010; and (c) July 26, 2010

Credit: [Left to right]: R. Graham, N. Fadli, Y. Herdiana. Courtesy of ARC Center of Excellence for Coral Reef Studies