Human waste killing corals in Caribbean, says study

Scientists with the University of Georgia and Rollins College in Florida say that human sewage is the source of a coral-killing pathogen that causes white pox disease found in Caribbean elkhorn coral. They say the bacterium from humans is now rampaging through coral reefs in the Caribbean.

Scientist say those reefs were already in slow decline, but they took a huge hit starting in 1996, when white pox appeared in the Florida Keys.

“Since that time, elkhorn coral — the species it affects — has declined 88 per cent in the Florida Keys,” said Kathryn Sutherland, a reef ecologist at Rollins College in Florida. “And we’ve seen similar declines elsewhere in the Caribbean.”

The coral is named for its resemblance to elk antlers, and is among the most important reef-building species in the Caribbean.

Sutherland and her colleagues soon found a culprit for the die-off — a bacterium called Serratia marcescens. It also happens to cause disease in human beings, notably hospital infections. But the scientists couldn’t prove cause and effect.

“In 2002, we could only speculate that human waste was the source of the pathogen because the pathogen is also found in the guts of other animals,” such as deer, Sutherland said.

She said she and some colleagues exposed the coral in the laboratory to bacteria extracted from sewage.

Traditionally, scientists think of diseases moving from animals to us, but “this is almost a man-bites-dog story,” said James Porter at the University of Georgia, a co-author of the study.

“This is a very rare and unusual evolutionary triple jump,” said Porter, adding that the bacterium “went from humans to the lower invertebrates — coral. It went from the terrestrial environment to the marine environment. And then it went from the anaerobic [low oxygen] conditions of our stomach to the fully oxygenated conditions on the reef.”

Porter said they are still trying to explain exactly how the bacterium makes coral sick, and why white pox appeared so suddenly and viciously.

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