The cobalt seas of Southeast Asia cover some of the most extensive coral reefs on the planet: vast, variegated architectures of limestone and living tissue that serve as iridescent underwater cities for countless plant and fish populations. But all it takes is a snorkel and a mask to discover one of the concealed tragedies of the modern era: the reefs are dying. For years environmentalists have pondered the causes, blaming pollution and earthquakes, sedimentation and the uprooting of mangrove swamps, never managing to concur on what was obliterating the kaleidoscopic glories and the ecological vitality of the living reefs.

The castles of coral are in trouble all over the world, but the reefs of Southeast Asia face their own special assault. Those looking for the culprit need only visit the Fook Lam Moon restaurant in Hong Kong's Tsim Sha Tsui district, where a large brown fish is swimming his final circles in an illuminated aquarium. The fish is a humphead wrasse, native to the waters of Indonesia, and in a few minutes it will be caught in a net by two burly chefs, steamed in the restaurant kitchen and served to a party of 12, who will pay $369 to savor its unique and utterly fresh taste. This wrasse's journey from a reef off Sumatra to a Hong Kong restaurant table has been furtive, circuitous and lengthy--up to two months--which explains the fish's high price on Fook Lam Moon's crowded menu.

Environmentalists have now discovered the greater cost of that exotic trade: the destruction of the reefs. The humphead, along with other tropical species, such as highfin grouper and coral trout, is captured by an insidious fishing method involving sodium cyanide, the murder weapon of many a paperback mystery. In measured doses, cyanide temporarily stuns fish, making them easy to catch; afterward, the toxin is naturally flushed from a fish's system. But there is no mechanism for purging the cyanide from the waters where it is sprayed. New research shows that the cyanide used to snag live fish for gourmands in Hong Kong, China, Taiwan and Singapore is poisoning the reefs. "Hundreds of tons of sodium cyanide are being pumped into the coral reefs of Southeast Asia," reports Robert Johannes, an American marine biologist who lives in Australia and works as a private consultant, in a comprehensive study released last October under the auspices of the Nature Conservancy, a U.S.-based international environmental organization. The result, he writes, is "a vast and expanding ecological tragedy that has gone largely unnoticed outside the region." Concurs Yvonne Sadovy, a lecturer in fish biology at the University of Hong Kong: "Only now is the scale of the problem being realized."

And the complexity. Like other conservationist contretemps of the recent past, such as the killing of elephants for their tusks, cyanide fishing involves consumers who want an exotic commodity, dealers who make a fortune selling it and impoverished producers--in this case, fishermen in the Philippines, Indonesia and Papua New Guinea--whose livelihood depends on the business. But unlike the demand for tiger paws or rhinoceros horns, which are used in comparatively small quantities in Chinese medicine, the market for live banquet fish is virtually insatiable in ever more affluent Asia. And there is much more at risk than a single endangered species. Coral reefs are formed from the limestone skeletons of tiny animals that are related to jellyfish. Ecologically, the reefs are to the oceans what forests are to continents: they are shelter and breeding grounds for fish and plant species that will disappear without them. An estimated 10% of the world's 600,000 sq km of reef has been destroyed during the past 50 years by myriad causes, including industrial pollution.

But in the Philippines, which has 33,000 sq km of reef, 90% of the coral is dead or deteriorated, and that destruction is increasingly attributable to a silent killer. Every day for the past 15 years, thousands of fishermen have pushed out to the reefs in humble skiffs to dive beneath the waters with plastic squirt bottles containing diluted poison. Cyanide fishing has become rampant in Indonesia, where reef deterioration is accelerating, and is moving eastward to the South Pacific and as far west as the Maldives.

The report by the Nature Conservancy attempted to bridge the gaps in research done in individual countries. "No one had investigated the problem systematically and regionally until Johannes," says Vaughn Pratte, president of the International Marinelife Alliance-Philippines, a U.S.-affiliated nongovernmental organization. Researchers did a six-month study tour of nine countries and finally zeroed in on the Philippines, finding both the center of the problem and its genesis.

In 1957 Earl Kennedy, a Chinese-Filipino businessman living in Manila, learned from aquaculturists that cyanide can be used to stun fish temporarily. He experimented in the saltwater lagoons of the mainland of Luzon and became the country's first exporter of such colorful species as angelfish and triggerfish for aquariums in the West. By the late 1960s, the Philippines had become the world's leading exporter of tropical fish.

In cyanide, Kennedy had found a better fish trap, and it didn't take long for the food industry to see its use in a trade more lucrative than angelfish. In the West most of the fish that are eaten are coastal and pelagic species, such as cod or tuna. But Asians have traditionally had a taste for grouper or snapper, which resides among jagged coral reefs and can't be caught with nets. Tropical fishermen paddled out to reefs in skiffs and caught them one by one. With time came outboard motors, making farther reefs accessible. The 1970s saw the development of dynamite fishing--a method that killed the fish in large numbers and was later outlawed--and cyanide, which dramatically boosted fishermen's daily yields. Then the Asian economic boom of the 1980s spurred demand for restaurant fish that, because of cyanide, could be captured and delivered live. Overnight, a luxury item once reserved for emperors and tycoons came within reach of thousands of upwardly mobile Chinese families. The live-fish trade grew exponentially through the '80s and '90s. Today, according to the report, it totals 20,000 tons to 25,000 tons a year, or $1 billion at the wholesale level.

Chinese diners are convinced that a fish caught in the wild and kept alive until shortly before being served is superior in taste and texture to frozen fish or species raised in environmentally benign fish farms. According to the Nature Conservancy report, restaurantgoers in Hong Kong will pay four to eight times as much for such an Epicurean pleasure. And they definitely like their fish rare. After Indonesia banned the export of humphead wrasse in late 1995, orders skyrocketed. "Being endangered actually seems to spur demand," says a Hong Kong fish expert.

The trade begins in small fishing towns such as Siasi and Pangutaran in Sulu province. Four men climb into a motorized outrigger boat, equipped with food and water for up to two weeks--along with cyanide provided by the middlemen who will purchase the catch. When they reach reefs several miles out, a fisherman dives amid the coral, breathing through a crude plastic hose attached to a compressor on the boat. His targets are the groupers, which flit around reefs from five to 18 fathoms under the surface. The fisherman points a squirt bottle at the fish and sprays a solution of sodium cyanide and seawater. Within minutes, several dozen fish are stunned and netted by the diver. After many such operations, the diver surfaces and dumps his catch into a submerged net attached to the skiff. Twenty minutes later, the fish can swim normally; back on shore, they are placed in holding pens attached to the fishermen's shoreline residences. Within a few weeks, the fish have expelled the cyanide from their system and are ready to be hauled to the port of Zamboanga, on the southern island of Mindanao. Because cyanide fishing was made illegal in the Philippines in 1975, the fish are tested in a poison-detection center established a year ago. Only six fish have tested positive.

Placed in saltwater tanks aboard trawlers or packaged in plastic bags filled with seawater for shipment by air freight, the vigorously flapping fish are sent to Hong Kong, the major market and transshipment center for live food fish. Meanwhile, their former home is closer to death. After the fisherman squirts the cyanide, the first thing to perish is the reef algae, on which fish feed. Days later, the living coral starts to expire. Soon the reef loses its function as a habitat for the fish, which eat both the algae and invertebrates that cling to the coral. The reef becomes an underwater graveyard, its skeletal remains brittle, bleached of all color and vulnerable to erosion from the pounding of the waves.

In the outer reaches of the Indonesian archipelago, the business is similar, with a twist. In small fishing villages, the trade is typically controlled by the local Chinese restaurant, which outfits the fishermen with boats, rice, nets and cyanide. The restaurant takes ownership of the captured fish and stores them in vast floating cages, each species segregated in its own pen. When a minimum of five tons has accumulated, the restaurant receives a visit from a large trawler. Prices are negotiated, the fish transferred, and a new supply of cyanide is delivered for the future--even though cyanide fishing has been illegal in Indonesia since 1985.

Then the trawler heads home, in most cases to Hong Kong, regional hub of the trade. Some fish are unloaded at the Kwun Tong wholesale market and snapped up by eager restaurant buyers. Others are immediately dispatched to China, which consumes a third of the annual catch. Each large live-fish transport vessel carries as much as 20 tons of fish, worth between $250,000 and $400,000, and its import into Hong Kong falls under laws written for the aquarium trade. It is exempt from health controls and doesn't even show up in trade statistics. That suits the middlemen fine. "We are traders and businessmen," asserts Yeung Wei-sung, managing director of Wing Sang Sea Products, a major importer. "We only buy the fish. We don't care how they are caught."

Ending the blight of cyanide fishing will not be simple, and experts have already concluded that cracking down on the far-flung fishermen is futile. As with ivory and the skins of endangered wildcats, the best hope is to police the middlemen while educating consumers. The place to start is obvious. "Hong Kong is party to the destruction of the reefs," says Brian Darvell, chairman of the Hong Kong Marine Conservation Society. "It must recognize its global responsibility." That will be a challenge: the conspicuous consumers of Hong Kong, and their cousins throughout East Asia, have acquired a taste for which they are willing to pay a high price. What they apparently don't know or don't care about is that every stab of the chopstick destroys a piece of priceless, far-off coral reef.

--Reported by Sandra Burton and Lulu Yu/Hong Kong, Michael Shari/Jakarta and Nelly Sindayen/Jolo

WHAT TO DO

Diners in Hong Kong, South China and Singapore want their fresh, steamed grouper, the middlemen their profit and the fishermen a decent livelihood--all at the expense of the reefs. Some possible ways of untangling this twisted net:

Friendly fishing: Traditional methods of catching grouper, the main fish caught for food, are less harmful to the environment. In the Philippine province of Palawan, the nongovernmental International Marinelife Alliance has weaned fishermen from cyanide and retaught them the art of fishing with hook and line. In Indonesia's Kei Kecil island chain, 300 households of the Kei tribe refuse to use cyanide or dynamite urged on them by fishing companies. "The single most important mechanism for reducing cyanide fishing is to give local people more control over their own resources," says the Nature Conservancy's consultant Robert Johannes.

Cyanide testing: Instead of bans by individual governments on the use of cyanide in fishing, which are often ineffective, experts are studying a procedure practiced in the Philippines in which fish are tested for cyanide residue before shipment. Those that pass are issued a cyanide-free certificate and allowed to be exported. But fish merchants in locations such as Hong Kong would have to cooperate by purchasing only certified fish.

Myth busting: The Nature Conservancy recommends holding pub-lic "taste test" panels to determine whether wild fish kept alive until they are cooked really are superior in flavor or texture to those raised on fish farms, which aquaculturists are laboring to improve. The assumption is that the differences are, or soon will be, imperceptible--and that the myth of the better-tasting live reef fish is one of the most destructive marketing gimmicks of modern times.

--By Anthony Spaeth. Reported by Sandra Burton/Hong Kong