James Cook University
A sinister black band chewing through living corals on the world's coral reefs is a sign of what scientists fear may be an emerging global pandemic of coral diseases.
The black band of microbial infection advances at millimetres a day, steadily and remorselessly killing corals when conditions promote its spread, says Dr Bette Willis, a chief investigator in the Australian Research Council Centre of Excellence for Coral Reef Studies based at James Cook University.
"We're seeing more and more cases of disease outbreaks affecting corals, in Australia and round the world. A whole series of diseases seem to have emerged in recent decades," she said.
"This is particularly true in the Caribbean, where the speed and extent of mortality that disease is currently causing is unprecedented in the recent geological record" Dr Willis, Associate Professor at James Cook University's School of Marine Biology and Aquaculture, said.
There, new coral diseases take a range of forms. 'Black band', 'white plague', 'white pox', 'white syndrome' and 'white band' are names describing the appearance of different kinds of microbial assaults taking place on the corals of the world's warm oceans.
The first outbreaks were seen in the Caribbean in the 1970s, where they have devastated large areas of reef - and local tourism with it.
More recently, "corals that were recovering from a major bleaching event in 2005 were afterwards affected by a number of diseases," she said, in a pointer to what scientists suspect may be a link to this biological attack.
Outbreaks of coral disease have been detected on isolated coral atolls in the Pacific, along 600 kilometres of the east African coast from Tanzania to Kenya and on the world's largest reef, in Australia - indicating that the problem is planet-wide.
"Coral bleaching is associated with high water temperatures, and our research has shown a correlation between disease outbreaks and prolonged high water temperatures.
"Secondly, the diseases appear particularly to attack corals which are stressed as a result of bleaching or some other factor making them more susceptible."
"The news is not all bad - sometimes the coral recovers. In the Marshall Islands, of 100 corals attacked by white syndrome, about a third died but the rest survived and began to recover."
The diseases appear to be a combination of bacterial, protozoan and fungal infections, which attack different corals in varying ways - hence the diversity of appearance. What triggers them - apart from a warm ocean and coral stress - is unclear.
"Organic carbon and land-derived nutrients provide a food source for bacterial growth, and one theory is that increased inputs of these nutrients into the oceans are giving the microbes enough of a boost to attack the corals."
"We have to consider that global warming may be an important factor in some of these diseases," Dr Willis said. "So too may exploitation leading to shifts in community structure, as healthy coral systems are more resistant to disease. We may have to face the fact that human activity is multiplying the challenges to coral health."
"We now find signs of coral disease wherever we look for them around the world. Diseases are a natural part of any community, but despite the difficulty of scanning vast areas of reef, they weren't as obvious before."
Scientists have been scanning the GBR for years and it was not till the great bleaching event of 2002 that they first noticed a substantial rise in the appearance of 'white syndrome' on some reefs. Increased abundance of black band appeared off Pelorus Island in January 2006. However, so far, disease outbreaks on the GBR have been seen on only a small proportion of reefs. While the rise of disease is a serious concern, the GBR remains one of the healthiest coral reef systems in the world.
International marine scientists and park managers recently held a workshop in Zanzibar, Africa, to raise awareness about coral disease in the region and form a monitoring network to provide advance warning of impending outbreaks. Scientists also met recently in Hawaii to develop standard global protocols for identifying and reporting coral diseases in the Indo-Pacific and to develop a strategic response plan in the event of disease outbreaks.
Editor's Note: Original news release can be found here.
