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Posted May 2009

Bacterial infections causing a devastating disease killing
off corals in the Caribbean, and more recently the Pacific, have been linked to global warming.

James Cervino, a professor at Pace University and research scientist at Woods Hole Oceanographic Institute, and co-workers have identified a group of four new vibrio bacteria that combine with existing vibrio to attack zooxanthellae (algae that function as photosynthetic symbionts for coral). If their zooxanthellae die, the corals starve.

Death by yellow band disease is recognised by the pale yellow or white lesion found on the coral surface.

Cervino’s team provide the first evidence of yellow band disease in the Pacific and show that although different types of coral were attacked by the bacteria, the vibrio pathogens responsible were the same ones causing the disease in the Caribbean.

While the bacterial infections occur at normal ocean temperatures, warmer temperatures increase the virulence of the disease. It can be initiated at 25°C, but yellow band disease expands rapidly as water temperatures reach 29–30°C.

The researchers conclude that “if global warming-induced thermal stress and YBD infections continue to proliferate in the tropics, this will contribute significantly to the collapse of the remaining reef habitats in the next decade”.

They also noted that an interesting topic beyond the scope of their study was “how part of this bacterial consortium was found in distant and separated geographic locations such as the Pacific and Caribbean”.

A recent global review of coral reefs by Bernhad Riegl, from the National Coral Reef Institute in Florida, and colleagues found that diseases are one of the biggest threats to coral reefs and are predicted to worsen under global warming.

It is not yet known whether these diseases are endemic to the regions where they are appearing or have been spread by human activities.

Caribbean reefs in particular have been ravaged by numerous diseases. The recognition of diseases as a significant cause of coral reef declines is relatively recent, and very few of the pathogens responsible have been identified.

References
Cervino JM, Thompson FL, Gomez-Gil B, Lorence EA, Goreau TJ, Hayes RL, Winiarski-Cervino KB, Smith GW, Hughen K, Bartels E. 2008. The Vibriocore group induces yellow band disease in Caribbean and Indo-Pacific reef-building corals. Journal of Applied Microbiology 105: 1658-1671.

Riegl B, Bruckner A, Coles SL, Renaud P, Dodge RE. 2009. Coral reefs: Threats and conservation in an era of global change. The Year in Ecology and Conservation Biology, 2009: Annals of the New York Academy of Science 1162: 136-186.