Global Warming, Bacteria Threaten Coral Health

Yellow band disease (YBD)-a bacterial infection that sickens coral colonies- is apparently getting worse with global warming, say researchers, who have now identified the bacteria responsible for the disease.

Researchers at the Woods Hole Oceanographic Institution (WHOI) have reported isolating the bacteria that cause YBD: a group of four new Vibrio species, which combine with existing Vibrio on the coral to attack the zooxanthellae, which are the photosynthetic symbionts of corals.

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YBD is characterised by a swath of pale-yellow or white lesions along the surface of an infected coral colony.

The discoloured band is a mark of death, indicating where the bacterial infection has killed the zooxanthellae. The coral host suffers from cellular damage and starves without its major energy source, and usually does not recover.

The study led by James Cervino, a guest investigator in the WHOI Marine Chemistry and Geochemistry department, reported isolating the bacteria that cause YBD: a group of four new Vibrio species, which combine with existing Vibrio on the coral to attack the zooxanthellae.

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Cervino said that the broad distribution of the core group of Vibrio also helps explain the expanding incidence of YBD throughout the world's tropical oceans.

He said: "In the U.S. Virgin Islands, Florida, the Caribbean, YBD is one of the most threatening coral diseases."

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The Vibrio bacteria that cause YBD are part of a family with a reputation for disease.

"What we have are coral pathogens that are genetically close to shellfish pathogens," said Cervino.

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The researchers grew Vibrio pathogens together with healthy coral and found that YBD infection occurs at normal ocean temperatures, but that warmer temperatures made the disease even more virulent.

Cervino explained: "Contrary to what many experts have assumed, this disease occurs independently of warming temperatures."

However, when the temperatures go up and the corals are already infected, the infection becomes more lethal.

He added: "Thermal stress and pathogenic stress are a double-whammy for the organism."

He also said that with the Vibrio core group occurring in tropical oceans all over the world and water temperatures on the rise, the prognosis for corals and the spread of YBD is rather grim.

The study is published in a recent issue of the Journal of Applied Microbiology (JAM).

Source-ANI
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