Sleuthing scientists pinpoint coral killers

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It might not quite be Sherlock Holmes, but scientists are now able to use technology normally used in diagnosing human diseases to detect elusive diseases that are killing countless numbers of coral reefs around the world.

Hard coral cover on Caribbean reefs has decreased by an average of 80% in the past few decades, with Indo-Pacific reefs having an estimated loss of 50% over the same period. In recent years coral diseases have emerged as significant threat to coral ecosystems alongside other more familiar causes for decline such as; overfishing, pollution, habitat destruction, climate change etc.  

By using a new method that uses the presence of microbes to classify specific diseases, coral researchers and those responsible for managing reefs will be able to better identify coral infections and take more effective action to reduce the impact of a disease.

"Current classification of coral diseases is mostly based on a description of how the coral has deteriorated, such as the pattern of tissue loss and abnormal colours," says Joseph Pollock, a PhD student at the ARC Centre of Excellence for Coral Reef Studies. "This is an ineffective way to identify coral diseases because different diseases can often look very similar. For instance, in the Caribbean alone, more than six "white" diseases show the same characteristics of tissue loss exposing white coral skeletons."

As there are a number of different microbes responsible for coral diseases – viruses, bacteria and fungi amongst them – identifying which organism causes a particular disease is an important process that is required for effective planning of treatment of the disease.

David Bourne from the Australian Institute of Marine Science says. "Instead of relying on appearances to tell us what disease the corals have, we need to determine what's happening to them before the symptoms show. This will help us to control, or reduce the impacts."

Mr Pollock’s method utilises diagnostic technology commonly used for identifying human diseases, or in forensics.  "The technology is called quantitative-PCR (qPCR) and is often used in human medical research. qPCR works as a genetic fingerprinting technique that both detects and quantifies a specific DNA molecule in a sample. It can detect pathogens at even very low levels – as few as a couple of bacteria in a cup of seawater," Mr Pollock says.

The technology can also be used on water samples to gauge the general health of the wider coral reef environment, Mr Pollock says.

"This technology is sure to have many applications in the future as marine environments are put under pressure by multiple impacts from rapid coastal development, declining water quality, and climate change".

For further information see the open access paper available via PLoS PATHOGENS: Pollock FJ, Morris PJ, Willis BL, Bourne DG, 2011 The Urgent Need for Robust Coral Disease Diagnostics. PLoS Pathog 7(10): e1002183. doi:10.1371/journal.ppat.1002183

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