Under a Caribbean sky, the sea glitters like a field of shattered glass, and the beach glares so brightly that my eyes ache. Palm shadows loom featureless and razor-sharp, like black cutouts. As I slide into crystalline waters, the blazing sun gives way to a blue, soft-edged world ceaselessly in motion. I feel like Alice crossing into the looking glass.

Life dances all around. Sea plumes (Pseudopterogorgia spp.) wiggle like waving fingers, while the fleshy tentacles of a giant anemone (Condylactis gigantea) sway in perpetual currents that bend purple sea fans (Gorgonia spp.) like storm-blown trees. Blue and yellow fairy basslets (Gramma loreto) flit like falling confetti against a backdrop of craggy coral formations, and a bug-eyed squirrelfish (family Holocentridae) peers cautiously from a hollow. A trumpetfish (Aulostomus maculatus) hangs motionless, head downward, while concealed among gently waving stalks of sea rod. Spotting its prey, the trumpetfish lunges and sucks a small fish into its tubular mouth.

A dusky damselfish (Stegastes fuscus) is doing the aquatic equivalent of pacing, nervously crisscrossing a patch of reef. Damselfish often protect algae patches from other grazing fish, effectively cultivating little gardens on the reef. Tenaciously territorial, it occasionally darts at fish much larger than itself and chases them off. It even nips at my hand and tries to take a bite out of the front of my camera housing. Nearby, I notice what looks like a bouquet of frilly pink flowers stuck in a coral head. Suddenly, it is gone. A closer look reveals a small opening in the coral formation, the end of a tube built by a burrowing worm. The feathery flowers actually are the tentacles of a fanworm (Sabellastarte magnifica) extended to filter plankton carried by the currents. They are highly sensitive to movement and withdraw so fast they seem to vanish.

You cannot describe coral reefs without waxing poetic in lyrical words that now seem trite. The simple fact is that a coral reef is a fantasyland abounding with myriad extraordinary creatures, where shimmering light plays across a wondrous landscape speckled with rainbow-hued fish. But the facts themselves seem no less fanciful. These are intricate and ancient ecosystems where anemones, sea stars, nudibranchs, cephalopods, crustaceans, sponges, reef fish, and an eclectic array of other creatures—including the corals themselves—live in complex relationships and in delicate balance.

Yet as I drift over the reef, a bleak truth overshadows its bright beauty. Coral reefs are rapidly being destroyed: Around the world, these primeval ecosystems are succumbing to the multi-pronged assault of climate change, pollution, overfishing, development, and other human activities that threaten their survival.

By 1998, about 11 percent of the world’s coral reefs had already been destroyed, according to the Global Coral Reef Monitoring Network (GCRMN). Rising surface water temperatures, possibly due to global warming, worried scientists as well. Then the severe El Nio and La Nia hit. This weather cycle further warmed ocean currents and caused massive coral bleaching, a phenomenon in which increased water temperatures cause microscopic algae living within coral polyps to be killed or expelled, resulting in the coral polyps themselves whitening and usually dying. By the time the El Nio cycle had run its course, another 16 percent of the world’s coral reefs had been lost. Some may eventually recover, but it could take half a century to do so.

If destructive activities affecting coral reefs continue, as much as 60 percent of the world’s reefs could be gone within the next 30 years, according to GCRMN. These alarming predictions prompted the United Nations Environmental Programme to form a Coral Reef Unit, and for the UN Foundation to contribute $10 million to launch a major international cooperative effort to save reefs, called the International Coral Reef Action Network. Part of their plan is to create model sites around the world where reefs are protected and integrated with sound economic and social development, for coastal cultures often depend upon the sea’s bounty, and in many places the reefs are the prime source of food for people.

These underwater realms also play an intricate part in the greater web of life. Coral reefs are home to one-fourth of all marine species, by some estimates, including about 800 species of hard coral and 4,000 species of fish identified so far. According to Dan Brumbaugh, marine program manager at the American Museum of Natural History’s Center for Biodiversity and Conservation, estimating species diversity on coral reefs is difficult because few definitive studies have been done. “However, if extrapolations from research on several well-studied groups of reef species turn out to be true,” says Brumbaugh, “the species diversity of many groups of smaller, less well-studied animals is actually much greater than currently estimated—perhaps by a factor of five to ten. Marine microbes are possibly underestimated by a hundredfold or more.”

Found only in the tropics where water temperatures stay above 68 Fahrenheit, three basic types of coral reef exist: fringing reefs, barrier reefs, and atolls. A fringing reef abuts a landmass and forms when corals colonize rocks extending from shore. Barrier reefs, in contrast, lie offshore. They are separated from land by relatively shallow lagoons that stretch anywhere from several hundred yards to several dozen miles. At the far end of the lagoon, the reef rises to within less than two feet of the water surface and then drops off, often precipitously, to great depths. Atolls form in the wake of a sunken volcanic island. These reefs grow along the perimeter of the submerging volcano, and sand accumulating on the coral creates a partial ring of islands encircling a central lagoon above the crater. The reefs of the Caribbean, however, are unusual “bank-barrier reefs” that formed as a result of glacial activity within the past 20,000 years [see sidebar Concerning Caribbean Coral].

Corals, along with sea anemones and sea pens, belong to a class of invertebrates called Anthozoa, which arose about 570 million years ago and today contains about 6,000 known species. Of these, about 2,500 species are hard or stony corals. Named for their rigid skeletons, hard corals—along with other mineralizing organisms, like some sponges and algae—are the major reef builders. (Not all hard corals build reefs, however.) Other types of corals have more flexible skeletons, and include gorgonians (such as sea plumes, fans, rods, and whips), black corals, and soft corals.

Even a reef hundreds of miles wide begins with just a single polyp, a coral animal that ranges from just 1/16th of an inch to several inches in size depending upon the species. A drifting planula—the polyp in its larval stage—will settle and permanently attach to the ocean floor. As it develops, the young polyp secretes a hard calcium skeleton, called a corallite, on which it lives. Its thin, soft body is like a tube with tentacles that extend outward to feed—usually at night—but, when withdrawn, becomes an almost imperceptible coating of living tissue over the corallite. The polyp grows by budding in place like a branching tree limb to create a connected coral colony. Once large enough, the coral colony may reproduce sexually, creating planulae and setting them adrift. Many corals, especially branching species, also propagate when pieces break off during storms and regenerate where they settle.

That first colonizing planula is like a pioneer discovering a New World. A settlement is built, and other migrants begin to arrive. Dispersing planulae often attach to the limestone skeletons of dead coral colonies and, over time, the tiny settlement becomes a massive marine metropolis hosting a melting pot of species. Generation after generation of coral communities, growing upon the remains of countless previous ones, have created the world’s coral reefs. The largest, Australia’s Great Barrier Reef, is more than 1,200 miles long and millions of years old.

While coral reef ecosystems are teeming with life, the tropical waters they inhabit are nutritionally poor. To compensate, corals have evolved elaborate systems which, like an orchestra, must perform in perfect harmony. Corals are efficient predators, using their tentacles to feed upon microscopic zooplankton in passing currents. Yet not nearly enough zooplankton exist in tropical waters to feed the mass of coral. Additional nutrition comes from microscopic algae called zooxanthellae that grow inside each polyp. The algae contain chlorophyll and convert sunlight into energy, supplying food and oxygen for the polyp. This symbiotic relationship also benefits the algae, which are well protected inside the polyp and get vital nutrients such as carbon dioxide and nitrogenous compounds from the coral’s waste products. Since zooxanthellae require sunlight, reef corals grow in clear, relatively shallow waters. It is the loss of these zooxanthellae that causes coral bleaching.

While climate change may pose the greatest problem to reefs in the long run, destructive human activities are wreaking irreparable havoc right now. Unlike bacteria and insects that can evolve in response to antibiotics and pesticides because they “live fast,” Brumbaugh explains, reef-building corals’ far longer life-spans and slow rates of reproduction allow little chance for adaptive evolution to occur.

Overfishing and destructive fishing methods for food and the pet trade are causing the most severe damage to coral reefs today. Explosives are used to kill and catch fish, and cyanide is squirted into coral heads to stun hiding fish so they can be collected for home aquariums. Fish traps built for large fish often kill many smaller ones as well, and lost traps continue to lure and kill fish for many years. Such unsustainable fishing practices not only wipe out species on a reef but further upset the ecological balance. Serious overfishing in Jamaica—coupled with a die-off of sea urchins (Diadema antillarum), the other major algae grazer—left algae free to grow unchecked and to out-compete, and eventually eliminate, much of the live coral there.

Many coastal communities could not exist without coral reefs. Natural breakwaters, the reefs buffer waves and surges rolling in from the ocean, protecting homes and preventing erosion. In the Maldive Islands, coral is harvested in huge amounts for building material. Low-lying islands there have suffered great damage from storms—damage that might have been mitigated had reefs been left in place.

Development on land directly affects coral reefs. Deforestation leads to the erosion of tremendous amounts of soil into the sea. Settling on a reef, the soil smothers coral and blocks sunlight from reaching the zooxanthellae. Dredging for boat channels further stirs up coral-choking sediment. Pollution is a growing problem, too. Freshwater and soil runoff can pick up toxic agricultural and industrial chemicals that are carried to the reef. And then there is untreated sewage, bilge waste, oil spills, thermal effluents...the list goes on and on.

Tourism generates further problems as well as revenue. Boat anchors being dragged across a reef obliterate swaths of coral. Divers and snorkelers frequently damage coral [see sidebar Reef Etiquette] out of ignorance if not willfulness. On a dive in the Bahamas, I was hoping to photograph flamingo tongues (Cyphoma gibbosum), a leopard-patterned snail commonly found on sea fans. As sea fans undulate in the currents, polyps lining their lacy skeletons feed on passing zooplankton. Flamingo tongues eat the polyps but seem to do so at a pace that allows the polyps to regenerate. Usually, flamingo tongues are not hard to find. I was in an area with a lot of sea fans, but I couldn’t find any of the distinctive mollusks—until, back on the dive boat, I encountered a diver bragging about the “beautiful spotted shells” he had collected for his girlfriend. They would not remain so beautifully patterned for long. The colorful spots on a flamingo tongue cover a diaphanous mantle that the snail extends over itself but pulls in when threatened, ultimately leaving just a bare, peach-colored shell in a collector’s now smelly dive bag.

Since that incident more than a decade ago, conservation and diver education efforts have increased significantly, but so have the stakes. We still don’t even know all coral reefs have to offer. They may well be the pharmacies of the future. Life-saving medicines, such as the AIDS drug AZT—which was derived from chemicals in a Caribbean sponge—already are in use. Numerous other reef-derived remedies for serious illnesses currently are being explored. In fact, half of all new drugs being tested have marine origins, many from coral reefs. As we lose reefs, we also lose the possibility of ever finding these cures. And a coral reef destroyed is not easily replaced. These venerable edifices can only be created the old-fashioned way—one polyp at a time.

Not long ago, I dove at one of my favorite places: Anse Chastenet, a resort in St. Lucia. As I swim from the beach, the sandy bottom slopes gently downward. At a patch reef before the drop-off, stoplight parrotfish (Sparisoma viride) browse on coral, and a spotted moray (Gymnothorax moringa) gracefully glides into a hole. I reach the ledge, and the bottom is suddenly gone.

At about 60 feet, I level off and follow the contour of the wall. Looking up, schooling fish arc around great corals and sponges against a backdrop of every possible shade of luminous blue. The reef seems so monumental and timeless that I can imagine the first European explorers sailing over these same coral heads. What’s more difficult for me to imagine is that reefs that have survived for millennia could be gone in our lifetimes.

MORE!: Concerning Caribbean Reefs, Reef Neighbors, Reef Etiquette

—Robert Rattner has visited more than 40 islands, on land and underwater, to document the people and nature of the Caribbean, and has also helped develop and implement wildlife conservation programs on several islands. His photographs and articles have appeared in numerous magazines.

Zoogoer 30(4) 2001. Copyright 2001 Friends of the National Zoo. All rights reserved.