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Human Waste Killing Caribbean Coral

When White Pox disease infects coral, as in this case from the Upper Keys in Florida, it causes white blotches by killing the overlying coral tissue and revealing the coral’s white limestone skeleton underneath.

First documented case of human pathogen infecting a marine species

In the first documented case of a human pathogen infecting a marine species, U.S. scientists say a bacterium in untreated human sewage is killing coral along the Florida coast and in the Caribbean Sea.

The finding was reported this week in the Journal PloS One.

Over the past decade, the once-abundant elkhorn coral in Floridian and Caribbean waters has declined by nearly 90 percent. Rollins College coral reef ecologist and report co-author Kathryn Sutherlandand says in 2003 her group identified the culprit, a bacterium in White Pox disease, known as Serratia marcescens.

"We knew when we discovered the pathogen that it was common in terrestrial environments, in human guts, in human sewage and that it is a pathogen that causes disease in humans.”

But researchers could only speculate that human waste was the source of the pathogen because the same microbes are found in the solid waste of other animals.

Finding the source

In order to determine the source of the pathogen, scientists collected and analyzed human samples from a waste water treatment facility in Key West and from other animals such as key deer and seagulls.

And, while they found the pathogen Serratia marcescens in these other animals, the genetic analysis showed that only the strain from human sewage matched the strain found in white pox diseased corals on the reef.

In a laboratory experiment, Sutherland and colleagues took small fragments of Elkhorn reef coral and inoculated them with the pathogen found in human sewage.

“We watched them for a month’s time to see if disease signs would develop. The strain that came from diseased corals and human waste water, we saw disease signs in four to five days.”

Sutherland says the study reveals a new disease pathway, from humans to wildlife rather than the reverse model seen in outbreaks such as bird flu or HIV/AIDS. “This is the first time that a human disease has been shown to cause population declines of Marine invertebrates.”

Waste water treatment

One obvious solution, says Sutherland, is better wastewater treatment. “A decade ago the people of Key West upgraded their sewage treatment from septic systems to advanced waste water treatment and today the entire Florida Keys is in the process of upgrading their waste water treatment.”

Sutherland says the new systems keep deadly microbes from the coast where water-related revenues contribute more than $3 billion a year to Florida and the local region. She says the study is a call for action all across the Caribbean - where many island nations still lack sewage treatment systems.

Healthy elkhorn can provide habitat for reef fish and protect the coast from severe storms. Yet despite efforts to protect it, elkhorn populations have not grown. Sutherland says that while her team studies the White Pox menace, numerous other threats - including warming sea temperatures and other marine diseases - continue to put the coral community at risk.