Photo: Swirling masses of Anthias fish over a coral reef

Anthias fish swirl over a delicate coral reef in Fiji. Hot waters in 2000 and 2002 caused widespread coral bleaching in Fiji. However, as this 2004 picture shows, some systems managed to recover.

Photograph by Darryl Torckler/Getty Images

By Mindy Pennybacker

Republished from the pages of The Green Guide

Coral reefs shelter low-lying islands from storm waves and flooding and produce beach sand and some of the best surf in the world. These benefits are eroding, however, as reefs are assaulted by pollution, silt, warming seas, cruise ships, and divers’ prying fingers and heavy feet. An estimated 10 to 27 percent of coral has perished worldwide, and 40 percent may be gone by 2010, according to the Global Coral Reef Monitoring Network. When it comes to human health, coral, like canaries in coal mines, may be providing early warnings to the rest of us.

More than half of Americans (54 percent) live in coastal areas, and in resort areas tourists increase the population. In 1999 Hawaii had 1.2 million residents and 6.7 million visitors, World Watch Magazine reports. But even those who live thousands of miles away affect coastal waters. What we produce on land, including nitrogen-rich sewage and fertilizer, can ultimately find its way into the seas. This nitrogen stimulates the growth of macroalgae, or seaweeds. "When there are higher nutrients, such as the nitrogen and phosphorous in sewage, we see a shift from coral communities to algal communities," says Paul L. Jokiel, a researcher with the Hawaii Institute of Marine Biology (HIMB). But there’s hope: Reefs can, and do, begin to recover when protected, as has been observed at Hawaii’s Kaneohe Bay.

As the town of Kaneohe grew in the 1950s and ’60s, increasing amounts of sewage flowed into the Coral Gardens section of the bay—one reason, among others, for a subsequent coral die-off, says Fenny Cox, a junior researcher with HIMB. Sewage is harming coral worldwide. While investigating the death of 38 percent of Florida Keys coral reefs over the last five years, University of Georgia researchers discovered bacteria and viruses found in human sewage in coral with deadly white pox disease. The study, reported in the April 2003 Environmental Health Perspectives, posits that the fecal microbes may have helped the infection to invade. The web sites of the U.S. Environmental Protection Agency, National Oceanic and Atmospheric Administration, and U.N. Environment Programme state that sewage hurts coral. In 1978 Kaneohe sewage was diverted to deep waters offshore. Today, Cox says, the bay is clear and in some areas corals are once again growing.

Other factors that scientists believe may have harmed coral in Kaneohe Bay, the Florida Keys, and elsewhere include silting, warming temperatures, and overfishing, because fish graze on algae. "If the fish population is in good condition then the reef can probably tolerate a certain amount of algae," says John Stimson, professor of zoology at the University of Hawaii. Jokiel also studies the impact of soil and silt runoff throughout Hawaii. "If you remove vegetation, whether through cutting down forests, overgrazing, or growing crops like sugarcane, where you leave no cover on the fields for a good part of the year, you get lots of sediments," Jokiel says. All of these practices, including dredging and filling along the coast, have occurred in Hawaii and resulted in silting of reefs. On the pristine north shore of the island of Kauai, Jokiel found that grading for a subdivision caused runoff, harming the reef.

In addition to silt, industrial sugarcane farming diverted water from the natural stream ecosystems where the Kanaka Maoli, the native Hawaiian people, grew their staple food crop, taro. The taro paddies, known as lo'i, cycled irrigation waters back into the stream. As streams dried up, estuaries lost the mix of nutrients, freshwater, and saltwater that had nurtured hatchling ocean fish.

"In traditional Hawaiian agriculture, water was not wasted. The relationship between the auwai irrigation systems and the stream was that of an expanded stream ecosystem. If water was too warm, it wasn’t going to work for either the stream life or the taro, so there was a limit as to how much water you could take and how far you could take it from the stream," says John Reppun, a community planner whose family has been growing taro in Oahu’s Waiahole Valley, in the Kaneohe Bay aquifer, since 1976. Forest leaf litter fertilized the taro, and both provided nutrients to the estuarial food chain. Scientists have linked stream flows to the health of fish populations in Kaneohe Bay, noting that the edge between freshwater and saltwater is where the highest diversity and biomass can be found—and the greater the stream flow, the bigger the edge, as reported in Environment Hawaii.

A 25-year effort to restore the ecosystem and lo’i has resulted in the return of waters to Waiahole stream, which now flows at about half its pre-diversion rate. Tiny indigenous hihiwai shellfish, which migrate during their life cycle from the stream to the reef and back, have been reintroduced. However, Reppun notes, it remains uncertain whether the hihiwai can return upstream through silty runoff from housing developments.

Hawaii and its reefs are now facing what may be a historic turning point: as vast sugarcane and pineapple plantations close, this acreage could be converted to diversified, sustainable agricultural uses that will better control erosion. On the Big Island’s Hamakua Coast, formerly planted in sugar, farms are starting to grow dryland taro, vegetables, and vanilla beans. In Waipio Valley, water once used for cane is being returned to its natural flow—in part to restart waterfalls that attract tourists, says Jeff Mikulina, director of Sierra Club Hawaii.

At other places, such as Koa Ridge on Oahu, agriculturally zoned land is coming under pressure from housing development, Mikulina notes. Development and urbanization mean more hard-surfaced roads and driveways to conduct runoff, more fertilizers and wastewater from individual households, and greater consumption of freshwater. According to the Sierra Club fact findings in a Koa Ridge challenge, in 2002 the Hawaii State Commission on Water Resource Management estimated that all of Oahu’s groundwater "may be fully committed in less than 20 years."

Sewage runoff hurts humans too. The Natural Resources Defense Council reports that in 2001 there were 13,410 beach closings and swimming advisories nationwide. Eighty-seven percent were due to high levels of pathogens after heavy rains or sewage spills, a 19 percent increase over the previous year. The most common ailments from swimming in polluted waters are gastroenteritis (nausea, diarrhea, headache, and fever) and infections of the eye, ear, nose, and throat. Sewage contamination also frequently causes poisoning in shellfish consumers.

In a hopeful development, sea whips, slugs, sponges, and other reef organisms have provided promising treatments for human pain, inflammation, leukemia, and infections. Yet as the ocean, like Earth’s atmosphere, warms due to fossil fuel burning, we stand to lose this vast medicine chest before we can explore it. Temperatures just 1.8 degrees Fahrenheit (1 degree Celsius) higher than the summer maximum can cause symbiotic algae to flee corals, which then become "bleached," that is, they lose their color and energy source and die. As polar ice melts, sea levels are rising an average of 0.04 to 0.08 inch (1-2 millimeters) per year. For Pacific islands, such as the Cook and Marshall Islands, Micronesia, and Tuvalu, coral death removes a crucial protection against land loss.

The ocean is a living membrane that connects all our shores. Coral reefs are the ocean’s bones, the cradle of life, and an indicator of global environmental health. "What would I tell a consumer? Lead a simpler lifestyle," Jokiel says.

Share

How to Feed Our Growing Planet

  • hub_tease2.jpg

    Feed the World

    National Geographic explores how we can feed the growing population without overwhelming the planet in our food series.

See blogs, stories, photos, and news » »

@NatGeoGreen on Twitter

National Geographic Magazine

  • Photo: Rare caper flower in Hawaii temps a honeybee

    Pollinators

    They are the Earth’s pollinators. And they come in more than 200,000 shapes and sizes.

  • Photo: Rapidly growing city-state of Dubai

    Age of Man

    It’s a new name for a new geologic epoch—one defined by our own massive impact on the planet.

Get More From the Magazine »

The World's Water

  • change-the-course-dry-co.jpg

    Help Save the Colorado River

    NG's new Change the Course campaign launches. When individuals pledge to use less water in their own lives, our partners carry out restoration work in the Colorado River Basin.

  • water-grabs-mali-4x3.jpg

    Water Grabbers: A Global Rush on Freshwater

    A special series on how grabbing water from poor people and future generations threatens global food security, environmental sustainability, and local cultures.

Learn More About Freshwater »