Coral Reefs: Canaries of the Sea

Coral reefs provide habitat for up to three million marine species, including canary-yellow butterfly fish, tangs and Moorish idols; they 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 10-27 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 (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, Ph.D., 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, Ph.D., 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. Their study, reported in the April 2003 Environmental Health Perspectives, posits that the fecal microbes may have helped the infection to invade. The websites of the U.S. EPA, 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, and today the bay is clear and corals are once again growing in some areas, Cox says. 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, Ph.D., professor of zoology at the University of Hawaii.

Jokiel also studies the impact of soil and silt runoff through-out 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, resulting 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 farming of sugarcane caused diversion of water from natural stream ecosystems where the Kanaka Maoli, the Native Hawaiian people, grew taro, their staple food crop, in paddies known as lo'i and cycled irrigation waters back into the stream. As streams dried up, estuaries lost the mix of fresh- and saltwater and nutrients 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 fresh- 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 twenty-five-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 prediversion 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 an historic turning point: As vast sugarcane and pineapple plantations close, there is the potential for this acreage to be converted to diversified, sustainable agricultural uses that will better control erosion. On the Big Island’s Hamakua Coast, formerly planted in sugar, farms growing dryland taro, vegetables and vanilla beans are starting up, while 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, though, 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; fertilizers and wastewater from individual households; and greater consumption of freshwater, a limited resource that is under pressure worldwide. By Hawaii State Commission on Water Resource Management estimates in 2002, all of Oahu’s groundwater “may be fully committed in less than 20 years,” according to Sierra Club findings of fact in a Koa Ridge challenge.

Sewage runoff hurts humans too. In 2001, there were 13,410 beach closings and swimming advisories nationwide, 87 percent of which were due to high levels of pathogens after heavy rains or sewage spills—a 19 percent increase over the previous year, the Natural Resources Defense Council reports. The most common ailments from swimming in polluted waters are gastroenteritis (nausea, diarrhea, headache, fever) and infections of the eye, ear, nose and throat. Sewage contamination is also a frequent cause of poisoning in consumers of shellfish.

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 the burning of fossil fuels, we stand to lose this vast medicine chest before we can explore it. Temperatures of just 1° Celsius higher than the summer maximum can cause symbiotic algae to flee corals, which lose their color and energy source and die, in a widespread phenomenon known as “bleaching.” As polar ice melts, sea levels are rising an average 1-2 millimeters per year. For Pacific island nations, such as the Cook and Marshall Islands, Micronesia and Tuvalu, the death of coral is removing 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,” Dr. Jokiel says. See What You Can Do’s.