If you were a tropical fish living in the Caribbean Sea, there's a good chance you would have spent your youth darting between the roots of mangroves. These saltwater-loving trees dominate many of the world's tropical coastlines, providing shelter from predators for vulnerable young fish and food for a wide variety of marine species. Mangroves also protect shorelines from erosion and hurricanes. But now it's the mangroves that need protection. Ann Dornfeld reports from the U.S. Virgin Islands.

It's a brilliantly sunny, gusty day on the island of St. Thomas, in the U.S. Virgin Islands. Local fisherman Stanley Berry has backed his motorboat into an opening in this quiet mangrove bay. "I'm going [after] yellowtail snapper tonight," he says. "I'm doin' night fishing. See if I can catch something tonight, God spare life. I see he's got a hurricane blowing out here today," he adds with a laugh, meaning the 40-kilometer-an-hour wind that's kicking up.

Berry explains the red mangroves around this bay serve as a sort of daycare for the young fish he'll eventually catch. "If you have to snorkel around and check it out, you'll notice that all these little fishes are different type of grouper, snapper, you name it, all comes and all the baby ones come and hang around in there so the big fish don't eat 'em. It protects 'em. It's real good for the fish to come and spawn in here and stuff."

And the mangroves are "real good" for the rest of the bay. As they anchor in the sediment of the shallow water, the trees' tangled roots catch sediment from the land before it can seep into the water. Above the tide, mangroves' dry branches are home to birds and lizards. And mangrove forests provide a buffer zone that protects inland areas from storms moving in from the ocean.

David Olsen, director of the U.S. Virgin Islands Division of Fish and Wildlife, says island natives understand the value of the mangroves. But he says developers aren't as appreciative, pointing to one company that wants to rip out the red mangroves on this bay for new construction. "They would basically line the entire area with condominiums, have docks basically filling the entire bay, eliminate all the traditional use, and plant a little fringe of black mangroves."

Olsen says developers are required by law to leave or replant some mangroves. But there are many types of mangroves, and the species the developers want to plant don't extend their roots into the water, so they can't serve as fish nurseries.

This is a problem all over the islands, according to Rafe Boulon, Chief of Resource Management for the Virgin Islands National Park. "We have lost, in the Virgin Islands, probably 50 percent of our mangrove areas over the last half a century. Anytime people fill land, typically they're filling mangroves because they're selecting nice calm bays and that's where the mangroves are."

Mangroves are in much better shape on St. John, a 30-minute ferry ride from St. Thomas. That's because most of this island is a national park.

If you want to see firsthand why mangroves are so important, all you need is a mask and snorkel. The water is kind of murky and golden from fallen leaves. But it's rich with sea life. A short swim reveals a dozen different species of juvenile varieties of the fish you see when you snorkel or dive out in the deep water. And they're darting among the mangroves and chasing each other; they look like they're playing.

Alfredo Quarto, director of the Mangrove Action Project, says mangroves are being destroyed all around the world. Often, they're removed to build shrimp farms. Quarto says shrimp farming is often presented to local people as a source of jobs and food. But he says the loss of the mangroves means destruction of fish habitat, and the local fisheries are destroyed. "Most of the people are forced to leave their homes, because they can no longer fish. And the shrimp that's raised there, along these coasts, is shipped abroad. Is shipped to the northern, wealthy countries. Because they're selling us the cheap shrimp, the local people have no food."

Quarto says it's not just fisheries that are lost when mangroves are destroyed. Coastal areas also lose protection from violent storms. "Like in hurricanes in India in 1999, a major cyclone came into the Orissa Coast area and killed over 10,000 people. The people that lived behind the mangroves by and large were not affected by that same cyclone. Ones that lived in areas that were denuded or degraded mangrove areas were killed."

Mangroves that have been torn out or damaged can be replanted. But Quarto says people trying to restore mangroves often plant just one species in places where there are supposed to be many kinds. The Mangrove Action Project is teaching people that the best way to restore mangroves is to scatter the plants into the waves. That way, the tides distribute the baby plants as they would in nature.

Back in the Virgin Islands, Rafe Boulon says for people those new to the islands, a mangrove forest can seem like a swamp. It releases methane gas as leaf litter decomposes. And the roots collect trash that floats in from sea. "So hence, if they're dirty and smelly, there's no really good purpose for them, however," he stresses, "they're [a] very, very important ecosystem here."

The trick is to get that message to the many people who are building new homes in the Virgin Islands. That includes the United States' biggest generation ever of retirees, lured by a tropical paradise that relies on the mangroves.