February 15, 2013
Manmade Activities Behind Caribbean Coral Die-Off
April Flowers for redOrbit.com - Your Universe Online
A new study, led by the University of Georgia, solves the mystery of the dying Caribbean coral.Plunk down a wastewater treatment plant anywhere along a Caribbean coast and watch the coral reefs nearby start dying, by a means unknown to science.
"You'd have all the makings of a great mystery novel," says ecologist James Porter of the University of Georgia.
Unlike a novel, however, this story is true.
"Between 1996 and 2012, more than half of all corals in the Florida Keys alone had died," says Porter.
Elkhorn coral — Acropora palmata — suffered the greatest losses, disappearing from more than 90 percent of its former habitat. Elkhorn coral was once the most common coral in the Caribbean and now, it is protected under the U.S. Endangered Species Act.
"Most elkhorn coral that died in the Keys had signs of a disease known as white pox before its demise," says Porter.
Porter and colleagues Kathryn Sutherland of Rollins College and Erin Lipp of the University of Georgia ultimately identified human sewage outflows as the source of the pathogen causing white pox in the coral. The results of this study were recently published in the journal PLoS ONE.
"When we first identified the bacterium Serratia marcescens as the cause of white pox, we could only speculate that human waste was the source of the pathogen because it's also found in the wastes of other animals," Sutherland says in a statement.
S. marcescens is found in the gut of humans and other land-based animals. The researchers collected and analyzed samples from a wastewater treatment facility in Key West, along with samples from animals such as deer and seagulls, to trace the source of the pathogens. While the bacterium showed up in these other animals, genetic analysis revealed that only the strain from humans matched that found in white pox-diseased corals.
"The final piece of the puzzle," says Porter, "was to determine whether it was pathogenic to corals."
To determine this, the team exposed fragments of elkhorn coral to the strain found in humans. This exposure took place in closed laboratory tanks to eliminate any risk of spreading the infection to the populations of wild corals.
"Within five days, the human strain caused the disease in elkhorn coral," says Sutherland. "We then had definitive evidence that people were the source of the pathogen."
"These bacteria didn't come from the ocean. They came from us," adds Porter.
Serratia marcescens results in respiratory, wound and urinary tract infections in humans, as well as in meningitis and pneumonia. Hospital-acquired infections in newborn infants and in immune-compromised adults are also linked to S. marcescens infections.
"Humans are affecting the rest of the living world in many ways, including sharing our diseases," says Sam Scheiner, National Science Foundation (NSF) director of the joint NSF-National Institutes of Health (NIH) Ecology and Evolution of Infectious Diseases (EEID) Program, which funds the research. "This work demonstrates that such sharing may be happening in ways we would never have predicted."
The study was conducted over a five year period, and focused on how the coral pathogen is transmitted and the factors that drive the emergence of white pox outbreaks, including water quality, climate variability and human population density.
"We're concerned that disease incidence or severity may increase with rising temperatures," Lipp says, "so it's important to protect near-shore water quality in a changing climate."
The traditional model of disease transmission from wildlife to humans is the opposite of what has happened here. Wildlife to human transmission is well documented, like with the bird flu, for example. The transfer of disease-causing microbes from humans to marine invertebrates has never been proven before.
"This is the first time a human disease has been shown to cause deaths of a marine invertebrate," says Porter. "Bacteria from humans kill corals--that's the bad news. But the good news is that we can resolve it with advanced wastewater treatment facilities."
Wastewater treatment plants in the Florida Keys are being renovated and upgraded, which scientists hope will eliminate this source of bacterium.
"We need to address the water quality conditions that favored the establishment and survival of this pathogen in the marine environment," says Porter.