Coral Crisis: Global warming, trawling, pollutants threaten the world's coral population

If global warming accelerates over the next century, many scientists fear that the planet's biggest ecosystem could reach a tipping point with depleting nutrients in the oceans.

But a more immediate threat to marine health already has started — the slow dying of coral populations. Biologists estimate that about 70 percent of coral species are threatened and that 20 percent are damaged beyond repair. Coral is home to one-fourth of all ocean life.

The plight of coral spawned the 2008 International Year of the Reef, organized by the International Coral Reef Initiative, a partnership among governments and environmental groups. Leaders hope to draw attention to what they call one of the world's great natural treasures.

People need to conserve and manage coral systems before their losses multiply, said Ellycia Harrould-Kolieb, a researcher with Oceana, an international marine- conservation and advocacy group in Washington.

"I'd say things are pretty critical for corals at the moment," she said.

A spike in global temperatures will inevitably affect the ocean's coral community, according to researchers at UNC Chapel Hill, in a recent issue of the journal Science.

"Rising ocean temperatures are the most pervasive threat," the researchers report, "and almost half of the world's coral reefs have recently experienced medium- to high-level impacts."

But another report offers some good news. Scientists are studying natural processes that may prevent the oceans from warming beyond a certain point. A study by the National Center for Atmospheric Research in Colorado says that an ocean "thermostat" appears to be regulating sea-surface temperatures in a part of the Pacific where there is little evidence of coral bleaching — the loss of beneficial algae.

But global warming isn't the only problem. Experts say that coral reefs are vulnerable to man-made pollution, trawling, ocean acidification and other influences that undo what takes nature centuries to build.

"Coral is the equivalent to the rain forest in terms of diversity, but underwater," said Ilze Berzins, the head of biology operations at The Florida Aquarium in Tampa. "The life that coral reefs support is phenomenal."

Coral reefs aren't just home to an abundance of life — they act as buffers to crowded coastlines, Berzins said. "So when you lose coral reefs, you're more susceptible to storm and wave damage."

Coral reefs make up some of the oldest and most diverse ecosystems on Earth. Yet, they are sensitive to changes in salinity, ultraviolet radiation and nutrient levels. When healthy, they are a rich source of food for countless species, including more than 4,000 varieties of fish.

"Reefs provide homes, nurseries, feeding grounds and spawning sites to a diversity of life that is virtually unparalleled anywhere else in the world," Harrould-Kolieb said.

Because coral reefs live at the upper edge of their temperature tolerance, they are vulnerable to changes in temperature. Incremental warming above normal can put stress on the microscopic plants that live in coral tissue and provide reefs with their bounty of color. If overstressed, the plants die and the coral turns white, or bleached, exposing the calcium-carbonate skeletons of the coral colony.

But temperature changes may not be a uniform threat to coral. Parts of the ocean with warmer temperatures could be more resistant to the bleaching caused by higher temperatures, said Joan Kleypas, an oceanographer with the atmospheric research center.

"Global warming is damaging many corals, but it appears to be bypassing certain reefs that support some of the greatest diversity of life on the planet," she said. "Reefs that already are in hot water may be more protected from warming than reefs that are not."

To learn more about what you can do to help save coral reefs, visit the International Year of the Reef Web site at www.iyor.org and click on "Get Involved."

• Kurt Loft is a staff writer for The Tampa Tribune in Florida.