HALF MOON CAYE NATURAL MONUMENT, Belize — Fifty feet below the Caribbean's sun-dappled surface, schools of navy blue tangs drift like smoke, their languid progress mirrored by the gentle waving of purple sea fans and yellow tube sponges. A hawksbill turtle chugs along a ledge studded with elkhorn and brain coral, oblivious to the gaggle of adoring scuba divers trailing in its wake.
From this comparatively pristine vantage point, it's easy to see why naturalist Charles Darwin declared this necklace of mangroves, seagrass and submerged coral, stretching more than 150 miles off the Belize coast, "the most remarkable reef in the West Indies."
But troubles at the Western Hemisphere's largest barrier reef, like those at other "underwater rain forests" scattered across the globe, run deep.
A potent mix of coastal development, tourism, overfishing, pollution and climate change has damaged an estimated 40% of the Belize reef system, a UNESCO World Heritage Site that attracts more than a third of Belize's 850,000 annual visitors.
A recent string of "bleaching events" — where vibrantly hued coral turn a skeletal white — occurred when a spike in water temperatures that scientists associate with global warming expelled symbiotic algae living inside corals.
Worldwide, experts calculate that nearly 50% of coral reefs are under imminent or long-term threat of collapse through human pressures; 20% have been destroyed. And as a coalition of governmental and environmental groups trumpets 2008 the International Year of the Reef, anglers, snorkelers and divers from Cozumel, Mexico, to Cairns, Australia, are getting fish-eye views of an alluring but increasingly imperiled ecosystem.
In Belize, a former pirate haunt and British colony that gained independence in 1981, those dangers are particularly evident at Ambergris Caye (pronounced "key").
Once a favorite stop on the backpacker circuit and rumored subject of the Madonna hit La Isla Bonita, the narrow, 25-mile-long island has retained much of its "no shirt, no shoes, no problem" vibe. Golf carts and rusty bicycles still outnumber cars on the recently paved streets of tourist hub San Pedro, the island's only town (pop. 10,000).
Waterlogged revelers, many clutching Belize-brewed Belikin beers or concoctions made with local One Barrel rum, gather there on Wednesday nights for the "chicken drop" — a gambling exercise involving numbered squares and a defecating pollo.
But the island's dense mangroves and coastal forests, onetime shelters for jaguars, crocodiles and juvenile fish bound for the coral reef a half-mile offshore, are giving way to condos and resorts that have drawn the likes of John Grisham and the stars of the 2001, Ambergris-based reality show Temptation Island.
A casino just opened in San Pedro, and Ambergris Caye now has 107 hotels. That's double the number a few years ago, says Dorian Nuñez of the newspaper Ambergris Today, and a dozen large projects are in the works. Leonardo DiCaprio, who bought his own nearby island in 2005, reportedly plans to build an upscale eco-hotel there.
The developments' resulting sedimentation, combined with coral bleaching, hurricanes and other ills, worries locals such as Mito Paz, director of the San Pedro-based environmental group Green Reef.