By Cat Holmes
University of Georgia
With few large, modern sewage-treatment plants in the area, most human waste is processed by small-scale waste water treatment plants, or more commonly flushed into thousands of septic tanks and cesspits ( holes in the ground covered with concrete slabs).
Some homes, like most of the thousands of houseboats docked in the Keys, simply have waste pipes leading directly from toilets to the ocean. Older sewer lines also are known to leak untreated sewage into the groundwater.
Microbiologist Erin Lipp is looking to the coral reefs surrounding the islands for some answers.
“The [septic] fields are so porous that even the legal systems are not functioning,” said Lipp, who works with the University of Georgia Department of Environmental Health Science. A 42 percent increase in the population each spring, when tourist season arrives, adds even more strain to the islands' inadequate waste treatment systems.
Resulting human fecal contamination near shore is well- documented, Lipp said. “About 95 percent of the canals tested in the Keys tested positive for human viral pathogens like polio, hepatitis A and Norwalk.”
How much wastewater is reaching the region’s coral reefs further offshore, and to what extent it may be affecting them and offshore water quality are big unknowns. UGA ecologist Jim Porter has found the reefs have been decimated. He has documented a 38 percent decline in living coral coverage in the Keys over the last seven years.
Scientists suspect that there’s a connection between the contamination and the reef reduction, but offshore water testing hasn’t indicated the amount of human contamination that scientists suspect might be present, Lipp said.
“In a recent study, 13 out of 15 coral heads had the RNA of viruses on them but only one water sample indicated fecal contamination,” said Lipp. “In fact, offshore water testing has hardly detected any fecal indicators.”
Lipp thinks the corals themselves may hold the answer – that bacteria and viruses from human waste may be collecting on the reefs rather than floating around in the ocean.
“These bacteria and viruses prefer sediment or surface,” Lipp said. “They will colonize before they’ll simply float around.”
Furthermore, coral is a particularly hospitable environment for microbes. “Corals produce a mucus in response to stress,” she said. “It’s very sticky and a highly nutritional environment for bacteria.”
If human viruses and bacteria are collecting on coral as Lipp suspects, then the reefs would be a more accurate indicator of human fecal bacteria and pathogenic viruses offshore than water sampling.
Scientists have discovered bacteria indigenous to the ocean on the surfaces of corals that are two orders of magnitude higher than a few years ago, Lipp said She, along with co- investigators Dale Griffin of the U.S. Geological Survey in Florida and Joan Rose of Michigan State University will look specifically for human viruses and bacteria on the coral.
“Coral may be a more efficient and effective bio-indicator versus sampling hundreds of liters of water,” Lipp said.
With more accurate indications of human pathogens in near and offshore waters, scientists could create more accurate models to assess the risk of human waste to humans and the environment.
In a separate study, Lipp is investigating the origins of white pox, a coral disease that has destroyed a large part of the population of elkhorn coral in the Keys. White pox is caused by a bacterium that is also a human pathogen – it’s a common source of hospital infections – which suggests there may be a link between it and human activities.
Lipp, along with UGA researchers Kathryn Patterson Sutherland and Jim Porter, will use DNA fingerprinting to examine strains of this bacterium to determine the source.
Cat Holmes is a news editor for the University of Georgia College of Agricultural and Environmental Sciences.
(Cat Holmes was a science writer with the University of Georgia College of Agricultural and Environmental Sciences.)