Rising surface water temperatures and pollution place coral reefs at risk worldwide.

Over decades and centuries, succeeding generations of corals build layer upon layer of limestone skeletons, creating vast reef systems that can run for tens, even hundreds of miles. They're the most diverse marine ecosystems, harboring a myriad fish, invertebrates, sponges, and other creatures.

But corals thrive only in clear, clean, shallow tropical waters. In recent decades, such conditions are scarcer. Human population and development pressures have replaced coastal mangrove forests with cities, golf courses, fruit plantations, and aquaculture ponds. Soil erosion, sewage outfalls, and fertilizer run-off from the land have smothered corals with sediments and algal growth in much of the Caribbean.

Overfishing compounds the problem by removing creatures that feed on algae and clean the reef. Careless boaters and divers damage corals by touching, breaking, or collecting them. In the Philippines, desperate fishermen have destroyed entire reefs by using dynamite to capture remaining fish.

Staghorn and elkhorn corals are taking the brunt of the damage in the northern hemisphere, according to Jacques Carter, a coral-reef researcher at the University of New England in Biddeford, Maine. "The general pattern is that you first lose these branching corals. They become covered in fleshy brown algae, and later the algae begins overtaking the massive boulder corals."

But Belize - a small country of 200,000 at the base of the Yucatn - has taken impressive measures over the past decade to protect its coral atolls and extensive barrier reef, the longest in the hemisphere.

Marine reserves have been established to protect popular dive sites (which generate considerable revenue) and important fish and reef habitats.

"People traditionally thought about protecting a single species. Then people realized you couldn't do that without protecting their habitats," says Janet Gibson of the United Nations Development Program's Belize Coastal Zone Management Project. "But to protect habitats you have to take an even broader, ecosystem approach. That's what we're trying here in Belize." Recognizing the importance of the reef to Belize's development, UNDP funded a $3 million project to create an integrated management plan for Belize's entire coast. By regulating coastal development with an eye to minimizing impacts to the reef, the government hopes to put growth on a sustainable footing.

"Belize has an enormous potential for tourism, but it has to be balanced with environmental protection," says acting director of tourism Valerie Woods. While Belize has earned praise for its conservation policies, there are plenty of obstacles to carrying them out. Although clearing coastal mangrove forests is now illegal (it often results in the smothering of nearby reefs), the law is poorly enforced. Critics say developers' money seems to buy its way around zoning plans. Belize is also finding that there are threats to its reefs beyond its control. Pollution crosses national boundaries from Mexico or Honduras. Hurricanes can strike at any time, damaging reefs that may no longer be resilient enough to rebound as they once did.

Then there's widespread bleaching, a phenomenon believed to be caused by unusually high water temperatures and possibly linked to global warming. A small increase in water temperature - and Belize is having one of the hottest years on record - causes the algae in coral polyps to die. The weakened polyps often follow.

"We can't do anything about coral bleaching, but we can ease other stresses to the reefs to keep them healthy," says Ms. Gibson. "We must do it, because the reefs are part of what it means to live in Belize."

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