What coral reef specialists have long suspected—that human waste dumped into the ocean damages coral reefs—was confirmed last month by a new study in the journal PLoS ONE, at least for the endangered elkhorn coral in the waters of the Caribbean Sea off of Florida. Researchers were able to isolate a pathogen in human waste that causes white pox disease on the elkhorn, a species that has declined by nearly 90 percent in the past decade in the region.
We wondered: Is this just a Florida problem? So we called Stephanie Wear, director of coral reef conservation for The Nature Conservancy’s Global Marine Team, to get the…um, poop. Spoiler alert: The news doesn’t smell like a bed of roses.
Cool Green Science: How big an issue is this, both in the Caribbean and globally?
Wear: This issue is actually pervasive throughout small island nations globally. I’m sure it’s an issue continentally, but that’s not where we tend to focus when we talk about coral reefs.
The majority of the Caribbean has wastewater treatment issues, and they’re employing a variety of strategies to deal with their sewage in the Caribbean—including not dealing with it.
When I lived in the Caribbean, it wasn’t all that uncommon for me to drive home and smell the stench of raw sewage along my route. Actually, sometimes I would have to drive through small streams of sewage flowing into the sea because a septic system had broken down or a storm had caused an overflow.
In the Pacific, there are many places where the ocean is your toilet—about 16 percent of people there are in that situation. For those people, there are no other options, and sewage treatment isn’t even on their radar. Their first priority is to improve their sanitation facilities—for instance, by getting a toilet—and only then can they think about how to treat sewage to protect the environment.
CGS: We know sewage is bad for human health—beaches get closed when there’s been a runoff from a storm. But why is sewage such a problem for coral?
Wear: Two problems: Nutrients and disease.
First, human sewage is full of nutrients, and coral reefs require very high water quality—which means clear water, free of nutrients. By definition, tropical waters are low in nutrients. So when you introduce nutrients, things just get fouled up.
Now, just how much nutrients are fouling things up is a matter of scientific debate. Coral reefs are being overgrown by seaweed—but is that because the nutrients basically fertilize seaweeds to grow faster? Or are the seaweeds growing out of control because we’ve overfished a lot of the herbivores out of these systems, like parrotfish? The answer is probably a bit of both, and it depends on where you are. There is good science being done on these questions, so we hope to have clarity on the issue in the near future.
About disease: We’ve always thought that human pathogens were a problem on reefs, but we hadn’t found the evidence yet. The exciting thing about the PLoS ONE paper is that there is now a smoking gun at least for one disease with one species. That knowledge helps managers make good decisions based on good science.
Bottom line: The impacts of sewage on coral might be incredibly damaging. We certainly know that they are a contributing factor to the “global phase-shift” that reefs in many places are undergoing—from coral dominated to algae-dominated reefs. Reefs made up of mostly algae instead of mostly coral are not healthy reefs.
CGS: Why not?
Wear: Everything changes with an algae-dominated reef—structure, productivity, food sources. Even the shape of the habitat, which is really important for providing shelter to the fish and creatures that live on and around the coral. Coral reefs provide structure for a wide suite of animals. Algae-based reefs can’t support a diverse assemblage of species.
Algae-based reefs aren’t good for humans, either. Coral reefs provide a natural barrier to wave energy, protecting people who live along coasts. When that’s gone, the protection is gone, too.
CGS: Do particular kinds of coral or fish get hit especially hard?
Wear: These are questions that we don’t really know the answers to yet, but we’re going to be seeing more research in this area. There’s a lot of discussion right now, for example, about snapper that are showing up diseased in the Gulf of Mexico—there’s speculation that this is due to the Gulf oil spill.
In the absence of answers, though, we should be using a conservative approach. We should be assuming that, if one species is susceptible, there are likely others, and we should be doing whatever we can to prevent exposure.
CGS: So what are some of the solutions—better sewage treatment? Improving socioeconomic conditions for those who live near reefs?
Wear: Human needs and marine community needs have to be addressed together. Obviously, untreated sewage is a public health issue, even if it doesn’t make it to the ocean. The question for groups like The Nature Conservancy is how to get governments to invest in better practices or to follow through on previous commitments—because in many cases they’ve said, “Yes, we will treat our sewage, or we will improve our standards or our conditions,” but they haven’t followed through. Supporting countries to follow through on these goals is what the Conservancy’s strategy is going to focus on.
But individuals can make a difference, too. If you’re in a community in the Caribbean or the Pacific or the Indian Ocean where you’ve got problems with your sewage treatment, getting involved in the process—and it’s very much a political process—is the way to go. One great example is in Bonaire, where a marine park manager I know became a huge advocate for water quality—he pressured the government to start doing tertiary treatment, which will take 10 years to implement, but in the meantime they’re putting in a temporary sewage treatment plant.
Ultimately, it’s about your own quality of life. You don’t want those contaminants in your environment. They will make it to you at some point. They find their way. They don’t disappear when you flush the toilet.
(Image: Healthy elkhorn and boulder corals on the reef at Del Este National Park in the Dominican Republic. Source: Jeff Yonover.)