Coral reef ecologists have found a potential answer to a persistent and troubling puzzle. The elkhorn coral, named for its resemblance to elk antlers and known for providing valuable marine habitat, was once the Caribbean's most abundant reef builder. But it has declined 90% over the past decade, in part due to highly contagious white pox disease, which causes large lesions that bare the coral's white skeleton and kill its tissue. Now, after nearly a decade of data collection and analysis, researchers have a possible cause of the affliction: human excrement. The finding represents the first example of human-to-invertebrate disease transmission and suggests a practical approach for halting the disease's spread.
Coral reef ecologists have found a potential answer to a persistent and troubling puzzle. The elkhorn coral, named for its resemblance to elk antlers and known for providing valuable marine habitat, was once the Caribbean's most abundant reef builder. But it has declined 90% over the past decade, in part due to highly contagious white pox disease, which causes large lesions that bare the coral's white skeleton and kill its tissue. Now, after nearly a decade of data collection and analysis, researchers have a possible cause of the affliction: human excrement. The finding represents the first example of human-to-invertebrate disease transmission and suggests a practical approach for halting the disease's spread.
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There have been several efforts to conserve the Elkhorn coral which have had mixed results. The Florida Keys National Marine Sanctuary has served as a protected region for the area’s coral species. The Florida Keys National Marine Sanctuary has also developed plans for the protection and restoration of elkhorn coral. Restoration efforts have included attempts to re-attach coral fragments that were broken off during hurricanes or by ships. Attempts to re-attach coral fragments have also occurred in Puerto Rico and the Virgin Islands but all have had limited success.
Diseases that affect elkhorn coral include white pox disease, white band disease, and black band disease. White pox disease is a disease that only affects elkhorn coral. It is caused by a fecal enterobacterium, Serratia marcescens. The disease is very contagious and commonly moves from one colony to its nearest neighbor.
"This is a really important bit of work," says coral researcher Thomas Goreau of the Global Coral Reef Alliance in Cambridge on the new study. "I would say they've now proven their case beyond any doubt."
Nine years ago, a research team led by coral reef ecologists Kathryn Sutherland, now of Rollins College in Winter Park, Florida, and James Porter of the University of Georgia, Athens, linked white pox to a bacterium called Serratia marcescens, which is found in the intestines of humans and a handful of other animals. In humans, Serratia can cause respiratory and urinary tract infections. But although Sutherland and her team strongly suspected human waste—stemming from septic tanks that leak sewage into the Florida Keys's porous bedrock—was the culprit, they had no proof that the disease didn't start with Key deer, cats, seagulls, or any of the Caribbean's other Serratia-harboring wildlife. "There was considerable skepticism—it was too easy to blame other things," Porter (an author) says."
To dispel any remaining doubt, the researchers cultivated small fragments of healthy, Serratia-free coral in the lab, and then exposed these to the human-specific strain. Within as little as 4 days, the healthy coral showed signs of white pox infection, they report today in PLoS ONE.
For further information: http://www.coral.org/node/5573 or http://news.sciencemag.org/sciencenow/2011/08/human-excrement-to-blame-for-cor.html
Photo: http://patricklynch.net/florida-keys-2008/molasses-reef-diving-lynch.html
