Bacterial blot

Pathogens behind coral bleaching, say scientists

Published: Thursday 15 May 2003

Delving deeper into coral blea (Credit: Walcott Henry)it is widely believed that coral bleaching is an epidemic which may soon kill half the world's reefs as climate change raises sea temperatures. What has been recently found is that some bleaching may actually be an infectious disease spread by a worm. Israeli scientists say they have studied a coral species, whose bleaching is triggered by a bacterium transmitted by a coral-feeding worm. If the same is true for other corals, scientists may be able to prevent the disease by targeting the worm vector.

The phenomenon was discovered by Yossi Loya and Eugene Rosenberg, who led a team from Tel Aviv University, Israel. According to them, the bacterium -- Vibrio shiloi -- is responsible for the bleaching of the stony coral Oculina patagonica which is found in the Mediterranean Sea. But researchers were mystified because the bacterium was only active during summer. To find out about its hideout during winters, they added a fluorescent chemical tag to the water around the coral. The tag got attached to the bacterium's dna. The researchers were surprised to see where the fluorescence showed up later. "I thought we would find it in the water, or at least in a sediment," says Rosenberg. But the strongest glow came from the marine fireworm, Hermodice carunculata . The researchers believe the worm harbours the bacterium and transmits it to the coral while feeding during summers.

But many biologists disagree with the findings. Ove Hegh-Guldberg, director of the Centre for Marine Studies, Australia, thinks mass bleaching events happen too quickly to be caused by an infectious disease.

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