Reefs Rife with Disease

Kim Tingley, writing for On Earth, stresses how important it is to do something about the fast-disappearing elkhorn coral:

As recently as 15 years ago, elkhorn coral, Acropora palmata, was the most common species of coral in the Caribbean. Its tall, antler-like branches provide important habitat for fish and other creatures and help protect beaches from erosion and storm surge by slowing down waves. But today more than 90 percent of elkhorn coral is gone — thanks in large part to a disease called white pox, which rapidly destroys the animals’ tissue, exposing blanched patches of the elkhorn skeleton below. Researchers first discovered white pox in 1996, and though they quickly identified the bacteria responsible, Serratia marcescens, they’ve only now determined where it’s coming from: human sewage.

“It’s the first time that we’ve seen such a devastating decline of a species because of a human disease,” says Kathryn Patterson Sutherland, a biology professor at Rollins College and a lead author of a new study linking S. marcescens to wastewater releases. In people, especially those with fragile immune systems, the bacteria can infect wounds and the urinary and respiratory tracts.

Though there are many well-known examples of animal diseases migrating to humans — swine flu, bird flu, and HIV, to name a few — the opposite phenomenon, known as “reverse zoonosis,” is rare. The white pox epidemic is the first-ever recognized case of reverse zoonosis in a marine invertebrate. Even more unusual are the boundaries the bacteria crosses to reach the elkhorn, jumping from a vertebrate species to an invertebrate species; from land to sea; and from the oxygen-free environment of our intestines to the oxygen-rich waters of the reef. Helping S. marcescens complete the transition are the fertilizers and other nutrients that increasingly pollute reef waters already warmed by climate change — the extra fuel and heat make the ocean more like the inside of our gut, where hundreds of species of bacteria thrive.

While it’s “bad news” that “humans are the source” of white pox, Sutherland says, the good news is that “we have the solution, and that’s wastewater treatment.” In 2000, Key West, Florida linked all of its residents to advanced treatment facilities — as opposed to septic tanks, which tend to leak through the key’s limestone bedrock into the ocean. Recent tests show the new system is successfully eliminating the bacteria from effluent, and the remainder of the Keys are following suit. But upgrades to those islands alone are expected to cost some $900 million — a price tag well out of reach of your average Caribbean nation.

In 2006, the National Oceanic and Atmospheric Administration listed A. palmata as threatened under the Endangered Species Act — a first for coral. Now it will be up to Caribbean residents and government officials to decide just what saving the elkhorn from extinction is worth. In addition to creating habitat and protecting coastlines, the corals draw in tourists hoping to dive or snorkel through vibrant healthy reefs. “They’re beautiful when they’re intact,” Sutherland says. “When you see a large, healthy, branching colony, they’re absolutely amazing.” Unless action is taken soon, though, those amazing underwater scenes could become restricted to the souvenir-postcard rack.

For original, see

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