As a naturalist, I have explored and written about the Everglades for the past 16 years. Now I am learning to appreciate how the health of the reef tract--a 220-mile-long, semicontinuous necklace of coral reefs that arcs along the Florida Keys from the state's southern tip out beyond the Dry Tortugas--is entwined with the Everglades, the Gulf of Mexico and the Caribbean Sea. In 1997, for example, federal researchers found that disease on Florida's coral reefs had increased nearly threefold. The disease may be linked not only to the draining of the Everglades and our own infatuation with the Keys, but to polluted runoff from nearby and distant lands. That understanding led to a gathering in October of federal officials from agencies with activities that likely affect the reefs. "I've never seen so many heads of agencies sitting in one room focused on one issue," scientist Gene Shinn of the U.S. Geological Survey told The Miami Herald.

"The Florida reef tract is downstream from everything," says biologist Steven Miller of the University of North Carolina at Wilmington. Yet here, 6 miles off the east coast of Key Largo, where he has taken me to see the reefs, even the water is a dazzling turquoise green. I see nothing that indicates this reef is under siege.

Miller's more educated eyes see trouble, however. We watch a pair of three spot damselfish, 4-inch-long herbivores that create algae farms. First, they scrape a patch of coral. Then, over time, the fish feed on algae that grow on the damaged coral, and large numbers of the fish can destroy patches of coral. Damselfish populations were formerly held in check by predatory fish such as groupers and snappers. Says Miller, "Habitat destruction and overfishing have set in motion a population explosion of damselfish." And three spot damselfish have shifted from branching coral to more sensitive coral heads as disease has wiped out much of the elkhorn and stag- horn coral formations.

Trouble or not, the scene is still a visual feast, and I wonder why the Florida barrier reef tract, third largest in the world, is not an underwater national park. Yellowstone, our first national park, supports 60 species of mammals, 6 reptiles, 4 amphibians and 300 species of birds, most of them migratory. On the other hand, the biodiversity of Florida's reefs and neighboring habitats is astonishing, on a par with a tropical rain forest. The list conservatively includes 500 species of fish, many large, most colorful; 5 species of sea turtles; 62 species of hard coral; 1,320 species of mollusks, mostly snails and clams; and between 500 and 700 species of sponges. And new species are still being discovered in Florida reef waters.

I quickly learn from Miller and others that in order to understand the problems facing the reefs, one must understand the nature of the reefs themselves. I'm not alone. Everyone on the Keys concerned about the subject--from dive-shop owners to tourists--is learning basic coral biology in order to comprehend what they can do to save the resource.

Reefs thrive on the shallow edge of tropical seas, most often off the eastern shore of continents where warm water currents brush the coast. Cold water kills reef-building coral, which is made up of colonies of tiny, jellyfishlike polyps. Each polyp--there may be billions in a large reef--absorbs calcium from the water and secretes a hard limestone skeleton. At night the polyps extend sticky, stinging tentacles from their skeletons to capture and consume small floating animals called zooplankton.

Low on the reef's food chain are algae, plantlike organisms that convert sunlight to food. Some live on coral skeletons. One type in particular, zooxanthellae, lives inside the tissue of the polyps. There the algae make up about half the weight of each fleshy polyp and are responsible for the beautiful color of coral.

Coral is the foundation of the reef community, providing the three-dimensional structure where fish and invertebrates live and feed. Some coral species are hard. Some are soft. Some branched. Some unbranched. Whatever the firmness and shape, every coral has a two-stage life cycle: the free-swimming larva and the stationary polyp. The larva is carried by currents, often far from the parent reef. If a larva settles on a hard, clean, silt-free bottom it may survive to become part of a reef. If not, it dies. Once the larva has landed, the coral never moves again.

The ocean currents that sweep through the Caribbean and the Gulf of Mexico converge along the west coast of Cuba to form the Florida Current, the birth of the Gulf Stream. "Florida's reef tract exists at the behest of the Gulf Stream," says biologist John Ogden, director of the Florida Institute of Oceanography. As the Florida Current flows past the Keys, larvae of all manners of life--from coral to fish--are deposited offshore. Baby lobsters, for example, drift from the Caribbean into Florida waters, where virtually all adult lobsters of legal size are caught each year. "Florida's lobster harvest, like the presence of the reef itself, is sustained by the greater Caribbean," says Ogden.

Present Florida reefs began developing about 6,000 years ago, after glacial melt water flooded the southern extension of North America's continental shelf. Although the reefs follow the curve of the Florida Keys, the largest reefs are off the upper and lower Keys. Historically, the reefs off the middle Keys have been affected by Florida Bay. The bay's waters pour through wide passes and bathe coral with water that at various times of the year is either too hot, too cold, too silty or too salty to promote vigorous growth.

One night in 1977, for example, a cold front chilled Florida Bay to 54 degrees Fahrenheit. Cold water flowing out of the bay killed branching coral all the way out to the Dry Tortugas. In recent years, increased salinity in Florida Bay has been linked to seagrass die-offs, which are a likely source of nourishment for massive algal blooms. The greater salt content is the result of increased use of water on land to accommodate farming and housing developments. That means less water flowing through the Everglades into Florida Bay. Driven by tidal cycles and the wind, the soup-thick blooms have moved eastward, out across the reefs. Studies suggest that bay sediment and algal blooms may have killed some of the already stressed coral colonies off the middle Keys.

Snorkeling near the northern end of the reef tract, I lift my head to listen to biologist Miller, who counts a flotilla of 36 fishing boats in the waters beyond us. He points out that visitation--whether by fishing boats, jet skis, snorkelers or divers--is one of the many problems that plague this lush and sensitive tropical community.

The waters are too accessible for their own good. The Keys' 175 marinas harbor more than 22,000 registered boats. Nearly all boats with outboard engines continuously deposit oil in the water. Although the reef tract is the third largest in the world, it is by far the most widely used. By comparison, Australia's Great Barrier Reef, which is 10 times larger, hosts about one-tenth the visitors. More than a million divers and snorkelers visited Florida's reefs in 1997. Anchors chip away at the reefs, and feet inadvertantly damage coral by bumping against it. Some people have gouged their initials into coral; others have removed living animals for home aquariums, and spearfishers have depleted the stock of large reef fish.

The islands are themselves the remains of a 100,000-year-old reef tract that became exposed to air when the level of the world's oceans dropped during the last Ice Age. The weathered limestone is a spider's web of fissures and cracks. When the islands' 80,000 year-round residents and four million annual tourists flush the toilet, wastewater goes to sewage treatment plants, septic tanks, cesspools or injection wells deep below the surface. "It doesn't matter where you store sewage," says biologist Miller. "There is strong evidence that sewage leaks into near-shore waters and growing concern that the sewage may eventually wash over the coral reef."

Nutrient-rich wastewater favors the growth of algal mats, which smother coral and renders visibility to ten or so feet, little better than a London fog. "Twenty years ago, we used to have days when underwater visibility was 70 feet down," says Joy Tatgenhorst, an environmental educator at the Florida Keys National Marine Sanctuary. "When blue water from the Gulf Stream swept over the reef, you could see 100 feet. Now, 30- or 40-foot visibility is the best we get off the central Keys."

Also clouding the sea is warm water from a nuclear power plant on Biscayne Bay that has killed coral more than a mile away and runoff from construction sites on the Keys that washes directly into the water and out across the reefs.

Pesticides and fertilizers from Central America, dust from the west coast of Africa and silt from the mouth of the Mississippi River reach the reefs by the same looping currents that transport coral and lobster larvae. In the summer of 1993, floodwaters from the Mississippi River lowered the salinity in Keys waters on the Atlantic side approximately 40 percent.

Through my snorkeling mask, I see a 5-foot-long barracuda in a coral canyon. Beyond it swims a score of brightly colored fish, possible meals for the impressive predator. A school of parrotfish cruises past. Several pause to bite off bits of coral, producing a dull chipping sound, audible underwater. These gaudy-colored fish crush coral (usually dead), digest the algae and then expel a white cloud of coral sand. A large parrotfish--they grow up to 2 feet long--may release more than a ton of sand every year. Much of the lovely white sand beaches of the Florida Keys is nothing more than fish poop.

According to Rob Bleser, owner of Quiescence Dive Shop on Key Largo, last year's El Niño winds frequently changed direction and washed beach sand back out to sea. Today, so much sand has been pushed offshore and suspended in the water that visibility is reduced. But male parrotfish are such an otherworldly shade of blue that they still shine through the sandy water 30 feet away from me.

El Niño events have increased over the past few decades. The good news is that they are accompanied by light hurricane seasons--the major natural threat to coral reefs. But they also bring a rise in summer water temperatures off the Keys. Whenever coral is stressed by a change in temperature or salinity that exceeds its threshold, it expels its colorful zooxanthellae. What is left is the bone-white frame of the coral, a condition known as coral bleaching. Although coral may survive the loss of its algae, almost all growth and reproduction stops until the algae recover.

If the chemistry and temperature of the water are unsuitable for a long time, corals are replaced by sponges and algae. Bleaching was first recorded in Florida waters in 1980 and intensified in 1983 and 1987. In 1990, bleaching was more severe off the Florida Keys. It was even worse in 1997. Because bleaching appeared during the two warmest decades of the twentieth century, many scientists blame its appearance on recent changes in worldwide weather patterns.

Bleaching is just one of many afflictions that kill coral. Black-band disease, caused by several kinds of blue-green algae that appears as a dark ring around the coral, was first reported in Florida in 1973. The deleterious algae invade coral that has already been damaged, and the disease has become common in areas of human activity. And there are a host of signs of other diseases, some of which so far are symptoms without known causes: red-band disease, yellow-band disease, white pox, rapid wasting disease, patchy necrosis, white plague type 1, white plague type 2 and sea fan fungal disease, a terrestrial pathogen that reaches the reefs in runoff, perhaps from the Everglades.

Some scientists believe that the increased amount of ultraviolet light from the depletion of the stratospheric ozone layer negatively affects coral. Others disagree. While scientists hotly debate the nature of coral disease, no one doubts that the reefs are in trouble, most likely from multiple stresses.

Coral is not the only species that is ailing. In 1983, the black-spined sea urchin all but disappeared from Caribbean reefs, including Florida's, the victim of an unknown waterborne pathogen. The queen conch--the large, edible snail with the flared pink lip that, outside the Keys, is most often associated with home aquariums, has yet to come back from overharvesting. There were major fish die-offs in Florida's reefs in 1980 and again in 1997.

The fate of Florida's coral reefs, however, is not "all gloom and doom," asserts Miller. In 1960, Florida set aside the world's first underwater park, John Pennekamp Coral Reef State Park. In 1975, Congress designated the nation's second national marine sanctuary off Key Largo. Six years later, the Looe Key National Marine Sanctuary protected a popular reef off Big Pine Key. In 1990, prompted by the grounding of three large ships on the coral reefs, Congress created the 2,800-square-nautical mile Florida Keys National Marine Sanctuary. Portions of the sanctuary were set aside as reserves, wildlife management areas and for research. Channels have been marked in the shallows to protect seagrass beds from propellers, and moorings have been set to tie boats to, which eliminates anchor damage on the reef.

Johnny Peacock, 44, a boat captain at Quiescence Dive Shop and a native of the Florida Keys, says "I'm not in favor of governmental intrusion that isn't necessary. This was necessary." When Peacock was a boy, everyone exploited the reefs. "My granddaddy butchered turtles for Tavernier restaurants. I still remember the turtles grunting and groaning and all the blood. When I was 10, I dreamed of killing turtles. I begged my granddaddy to let me do it. Now, its socially unacceptable. We've come a long way down here. And we still have a ways to go."

Vermont writer Ted Levin last wrote for National Wildlife about Florida's Everglades.

NWF Priority: Everglades Conservation
The health of Florida's coral reefs relies in large part on the health of the Everglades. The vast "river of grass" drains into Florida Bay and mixes with salt water from the Gulf of Mexico. Some of that mixture then washes out over the reefs. So much of the Everglades' water is now diverted for flood control and agricultural and urban development that the salinity of Florida Bay has increased. The saltier water has been linked to a chain of events that has resulted in massive algal blooms. The blooms may contribute to coral-killing diseases and other reef problems.

NWF and the Florida Wildlife Federation, an NWF affiliate, are working together to promote ongoing restoration of the Everglades watershed, as well as focusing on conservation of the Western Everglades. These efforts ultimately will benefit Florida's coral reefs.