The Explainer

Why is Sewage Pollution a Significant Threat to Coral Reefs?

Elkhorn coral at Jardines de la Reina, Cuba. Photo © Ian Shive

It’s easy to understand why sewage pollution is less than appealing. But is it really a problem for coral reefs? Research suggests that the potent and toxic cocktail spilling from our sewers poses a significant risk to corals and human health.

What’s Going On?

The most widely recognized pollutant within sewage is excess nutrients, which can fuel algal and seaweed growth that ultimately takes over a reef. But other toxic components of sewage — like fresh water and heavy metals — can weaken coral’s ability to fend off disease or kill them outright.

Most sewage finds its way into the ocean as either poorly treated or untreated discharge, or as stormwater runoff. In places with little to no infrastructure, like the developing world, the majority of wastewater goes untreated. For example, about 85 percent of the wastewater entering the sea in the Caribbean is untreated, according to the United Nations Environmental Program.

But the problem is not limited to developing countries. Old or poorly maintained infrastructure in the United States and other developed nations result in sewage overflow during heavy rain.

What the Science Says

Sewage pollution is a widespread problem: A full 96 percent of places that have both people and coral reefs have a sewage pollution problem, according to recent research by Stephanie Wear, The Nature Conservancy’s lead scientist for coral reef conservation.

The many pollutants within sewage are harmful on their own, Wear says, but often interact with each other to create more potent compounds. The primary pollutants within sewage include: fresh water, endocrine disruptors, heavy metals, pathogens, and other toxins, especially pharmaceuticals.

Why It’s Important

Sewage pollution threatens the ecosystem services that coral reefs provide people, including: shoreline protection, ecotourism, artisanal and commercial fisheries, and medicines. Environmental consultants estimate these services are worth $31 billion U.S. dollars each year.

It’s also a major threat to human health —fecal contamination sickens millions of people each year, and measures to curb sewage pollution will benefit both coral reefs and humans.

Additionally, sewage pollution threatens to undermine other marine conservation efforts. Wear says that current protection measures — like reducing overfishing or establishing marine protected areas — are pointless if the health of a reef is jeopardized by sewage pollution.

The Bottom Line

Sewage pollution is a major threat to coral reefs worldwide, killing corals and making them more susceptible to disease. Scientists, conservationists and managers recognize that sewage pollution is a significant threat, but are not devoting the necessary time and money to address the problem.

“We need to work beyond our comfort zones as conservationists and managers and reach out to the broad community to address this issue,” says Wear.

Justine E. Hausheer

Justine E. Hausheer is a science writer for The Nature Conservancy, covering the innovative fieldwork and research conducted by Conservancy’s scientists around the world. She has a degree from Princeton University and a master's in Science, Health, and Environmental Reporting from New York University. Justine has battled swarms of mosquitos, steep trails, and the wilds of the Papua New Guinea rainforest — all for a good story. When not writing about conservation science, she enjoys having far-flung adventures, long hikes, and waking up at dawn to bird. More from Justine E.

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1 comment

  1. Wow. An interesting article. I see it was written almost two years ago and yet, this is the first time I have heard, through any type of media, that sewage pollution is a contributing factor to the decline of our coral reefs. Up until now the only culprit I was aware of is the warming issue. I wonder if you are certainly correct in your statement that the problem is known but not being addressed, or whether the threat posed by pollution to coral reefs is not as serious as this article implies. Sounds plausible and definitely concerning. Thanks for the heads up.