Coral bleaching

Australian scientists say coral reefs in Southeast Asia and the Indian Ocean have been struck this year by the worst case of coral bleaching in more than a decade.

More than 500 types of coral, living in the so-called coral triangle, are particularly at risk of dying out due to bleaching, according to Andrew Baird of the Australian Center for Coral Studies.

The area covers roughly six million square kilometers (2.3 million square miles) of sea bordering Indonesia, Malaysia, Papua New Guinea, Philippines, Solomon Islands and East Timor.

"The scale is huge," Baird said, adding that the coral triangle and regions around it were undergoing dramatic changes.

"It probably extends from the Indian Ocean right into the coral triangle. There is also bleaching in the Philippines, and it's starting to get hot in the Pacific."

With increases in water temperature among the main causes, Baird predicted that current bleaching would reach a scale not seen since the last major global bleaching event in 1998.

Human impacts on currents

A current in the Indian Ocean brings warmer water to the region around Indonesia for about eight weeks beginning in May, but Baird said this was not the only reason why the water temperature was observed to be rising.

"This is a natural, cyclic event, but almost certainly human-induced climate change is increasing the intensity of the event," he said.

Coral bleaching occurs when environmental stresses, such as a relatively sudden increase in temperatures, shock corals into shedding the micro-organisms upon which they feed. Without their algae, coral lose their color and starve to death.

This process can occur when water temperatures increase by as little as one degree Celsius (1.8 degrees Fahrenheit) over their long-term monthly average.

That is a rate that has already been reached, according to Ove Hoegh-Guldberg, head of the Global Change Institute at the University of Queensland in Australia.

"If you look at the satellite sea surface temperature measurements, they are showing that seas are about one to three degrees warmer than the long term averages for the region," he said.

Already threatened

Such increases in temperature would be catastrophic for coral reefs, which are already in bad shape and will require years to get back to normal even if water temperatures were to drop immediately, according to Tony Mohr, head the Australian Conservation Foundation.

"Coral bleaching is showing that climate change is not something that's going to happen in the future, but something that's affecting systems right now," he said.

The loss of coral colonies also spells bad news for the many fish species that depend upon them for food.

"Everything that feeds on them (corals) will disappear as well," said Baird, who expects to see some fish species decline within a year.

Bleaching, which often results in the death of a coral colony, was called the greatest threat to coral reef systems by the United Nations Intergovernmental Panel on Climate Change.

The panel said 58 percent of the globe's coral reefs, which are home to hundreds of species of fish and other marine animals, are threatened by human activity.

Author: Udo Schmidt, Sean Sinico

Editor: Nathan Witkop