All over the world, coral reefs are endangered by rising ocean temperatures -- and travelers can see the effects firshand far off the Belize coast.
All over the world, coral reefs are endangered by rising ocean temperatures -- and travelers can see the effects firshand far off the Belize coast.
Sergio Hoare

Yes, the Water's Warm . . . Too Warm

By Juliet Eilperin
Washington Post Staff Writer
Sunday, July 15, 2007

The reef looked small from the boat, but once I plunged into the Caribbean I found myself gazing at what looked like a vast and intricate community, which was oddly dead and alive at the same time. In one section of Glover's Reef, which surrounds an atoll 55 miles off the coast of Belize, delicate spiny corals jutted out fiercely, surrounded by vibrant green and silver fish; in other places, only ghostly white corals remained, a testament to how warmer water temperatures had wreaked ha-voc deep beneath the sea.

When people think of habitats collapsing from rising global temperatures, they tend to think of frigid climes where polar bears have been frolicking on snow and ice for centuries. Think again. Coral reefs rank as one of the ecosystems most vulnerable to climate change: Recent scientific studies suggest global warming has already destroyed 20 percent of the world's reefs, and an additional 50 percent are in danger of disappearing.

Two aspects of global warming -- hotter and more acidic oceans -- threaten corals the most. In seven tropical regions where most coral reefs occur, waters have warmed between 1.3 and 3 degrees in the past century. Though that might not seem like much, a seawater temperature rise of 1.8 to 3.6 degrees above the summer maximum can trigger bleaching on many reefs. When bleaching occurs, the single-celled algae that live in symbiosis with a coral are expelled, and if the coral does not take up other algae within a certain period of time, it dies. Scientists call this bleaching because the living tissue of a coral is white; if the algae leaves, the coral loses its color because it no longer has a living creature inside. At that point the white limestone skeleton shows through.

At the same time that seawater temperatures are on the rise, absorption of human-generated carbon emissions has altered the oceans' pH level, making it more difficult for reefs and other marine organisms to construct their calcium skeletons.

"Climate change has and will continue to permanently alter the ecology of a large number of reefs throughout the tropics, particularly in the Caribbean," said Tim McClanahan, a senior conservation zoologist for the New York-based Wildlife Conservation Society (WCS) who has studied reefs from Belize to Kenya. "But there still are -- and will be -- some reefs in good condition for diving, particularly if we can manage them well in terms of fishing and other human uses."

Since coral reefs are scattered around the world and exist underwater, it's hard for researchers to say precisely how they're doing. In addition, some reefs host the kind of algae that can tolerate higher temperatures, which means those corals can survive even when the oceans get warmer. But a 2004 study of coral reefs worldwide estimated that since the 1950s, 20 percent of them have been destroyed and show no prospect of recovery; 24 percent of reefs are under imminent threat of collapse; and another 26 percent face collapse over the long term.

Protected areas like Australia's Great Barrier Reef do not face the same fishing pressure as an unprotected reef, for example, but even that reef could suffer from hotter and more-acidic seas. (Fishing poses a serious risk to reefs because it tends to damage the coral structures themselves, and because it deprives the reef of the fish and plant life that maintain the ecosystem's balance.) And just as scientists are seeking ways to preserve reefs in the face of these environmental pressures, travelers are exploring these habitats while they still exist.

A Stressed Environment

Few ecosystems exemplify this phenomenon better than Glover's Reef, part of a World Heritage Site and marine reserve. A patchwork of more than 800 reefs covering 90 square miles, the site is home to both a WCS marine research station and a smattering of small resorts. Although it's not the most luxurious place to vacation, it provides a way to witness both how climate change has damaged coral reefs and how they have resisted it.

With so many "patch reefs" scattered throughout the area, each amounts to a world of its own. In May I saw for myself, diving and snorkeling with shark scientist Ellen Pikitch, who directs Miami's Pew Institute for Ocean Science; WCS senior conservationist Archie Carr III; and Carr's 20-year-old daughter, Jenny. I was researching an upcoming book about sharks and wanted to see how these ancient creatures were faring in an environment that's under stress.

For an hour we dove around a reef that stretched for what seemed like a dozen yards. Despite its small size, the reef serves as home to an array of corals and fish, including a silvery barracuda, a gray nurse shark and parrotfish whose glowing colors indicate each one's sex and stage of development.

Two severe bleaching events in the 1990s, when water temperature spiked suddenly, have taken their toll on Glover's Reef, however. I swam past bleached reefs that resembled ghost towns, providing no sustenance to the tropical fish. Corals, whose limestone skeletons make them resemble rocks more than living organisms, help shelter young fish and provide a home for the plant life many fish need to survive.

Some types of coral -- such as staghorn, with its long, spindly branches -- are making a comeback at Glover's Reef. Scientists don't exactly know why, except that they are increasingly finding that some species are more resilient than others.

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