Coral reefs face the threat of extinction

As a result of global warming, ozone depletion, and pollution, these fragile marine growths are among the most endangered ecosystems on Earth.

IN SEPTEMBER, 1987, fishermen along the southwest coast of Puerto Rico reported that the reef's normally beige corals had turned bright white. At first, marine scientists Lucy Bunkley-Williams and Ernest Williams, Jr., assumed it was an ordinary case of bleaching. Corals bleach if stunned by a number of stresses, including extremely low tide, freshwater flood, pollution, and abnormally low or high water temperatures. Although they can die if the strain is not relieved, in the experience of both fishermen and scientists, bleaching normally was nothing to worry about.

When the two scientists took a dive to examine the reef, they found that its corals had bleached to greater depths than they ever had seen. They became more concerned as accounts of bleaching arrived from Puerto Rico's southern coast and the entire Caribbean. Soon, reports from throughout the tropics revealed the most widespread case of coral bleaching in history. Reefs in every major region of the world were touched.

Because many of the reports mentioned higher than usual water temperatures, some people thought that scientists had found the proverbial canary in the coal mine that would prove that global warming was under way, but this was not the case. Mass bleaching adds to the growing body of evidence--and may be a harbinger of what is to come--but only a long-term trend in global temperatures can confirm definitively that climate change has begun.

Although inconclusive, the debate over mass bleaching and global warming at least drew some needed attention to another global environmental trend--the decline of coral reefs. They already are suffering from a broad array of stresses, including coastal pollution from deforestation and crowded coastlines, which is choking them, and overexploitation by coral miners, fishermen, and tourists, who are destroying and depleting them. A study from the World Conservation Union and the United Nations Environment Programme (UNEP) in the 1980s found that people had damaged or destroyed significant amounts of reef off 93 countries. Reefs, it turns out, are among the most endangered ecosystems on Earth.

They are underwater marvels of fluorescent colors, fantastic shapes, and improbable creatures such as delicate purple sea fans, blood-red sponges, blue-spotted groupers, spiny pufferfish, snorkel-nosed moray, poisonous scorpionfish, giant clams and manta rays, and yellow-lip snakes. Their biological riches, though, hold value far beyond their beauty. After tropical rain forests, coral reefs may be the most biologically diverse ecosystem, holding a substantial portion of the underpinnings of life on the planet. They form what is thought to be the most species-rich ecosystem in the oceans, the crucible of life some 3,000,000,000 years ago. Covering just 0.17% of the ocean floor, an area the size of Texas, coral reefs are home to perhaps one-quarter of all marine species, earning them the title "the tropical rain forests of the oceans." Only the little-explored deep ocean floor could rival the marine biological diversity of coral reefs.

Like the rain forests, reefs hold considerable untapped potential to contribute to science, particularly medicine. The intense crush of life spawns unique chemicals such as kainic acid, collected from reef organisms in Japan and Taiwan, used as a diagnostic chemical to investigate Huntington's chorea, a rare, but fatal, disease of the nervous system. Other reef organisms generate chemicals useful for cancer and AIDS research. Corals themselves produce a natural sunscreen, which chemists are developing to market, and their porous limestone skeletons are promising for bone grafts in humans.

For the 109 countries whose shores are lined with more than 60,000 miles of reefs, the ecosystem is a national asset. Reefs provide immeasurable service by protecting coastal lands from the erosive forces of the sea. More than two-thirds of the world's sandy shorelines are thought to be eroding. The results of losing reefs can be seen in Tanzania, where formerly protected resort beaches are eroding at a rate of more than five yards per year. The bill for replacing these self-repairing breakwaters can run into the hundreds of millions, depending on the technology used.

Besides protecting coastlines, reefs also help form the idyllic white sand beaches and light turquoise lagoons that draw tourists to the tropics. Coastal tourism is the world's to the fastest growing industry, worth over $7.000,0010,000 annually in the Caribbean, the tourist Mecca. Other regions have seen coastal visitors double and triple in numbers over the last decade. In Southeast Asia, more than 110 existing and planned tourist sites are found along the coasts, many of which are reef-lined.

Locally, reefs are saltwater supermarkets of food and raw materials, especially for traditional coastal and island people. Pacific islanders receive up to 90% of their animal protein from reef fish, and people in Southeast Asia, the Caribbean, and parts of South Asia and East Africa derive a significant portion of the protein in their diets from the fish that live in these ecosystems.

Healthy reefs are thought to be among the most productive fisheries in the oceans--10-100 times higher per unit area than the open ocean. The total catch from reefs is estimated at 4-8,000,000 tons per year, approximately one-tenth of the fish caught for use as human food. According to John McManus, a marine scientist doing research at the University of the Philippines Marine Science Institute in Bolinao, coral reefs may account for up to 20-25% of the fish catch of developing countries.

Beyond their considerable value as a natural resource, reefs have intrinsic worth as one of the oldest living, thriving ecosystems. Mankind rapidly is extinguishing these intricate works of evolution that it is only beginning to understand.

Charles Darwin's five-year voyage on the HMS Beagle took him to the South Pacific, where he especially was interested in atolls, low islands that form on exposed reef. From their telltale circular shape with a lagoon in the center, he deduced that atolls were reefs that had formed on the shores of islands that since had sunk below the ocean surface. The reefs survived by continuing to build upward. Darwin wrote that "the naturalist will feel this astonishment more deeply after having examined the soft and almost gelatinous bodies of these apparently insignificant creatures, and when he knows that the solid reef increases only on the outer edge, which day and night is lashed by the breakers of an ocean never at rest."

The creatures Darwin referred to are the coral polyps, tiny sedentary relatives of jellyfish that live in colonies on the reefs. Individual coral colonies look like curiously fabricated tables, heads, branches, and leaves randomly arranged along the slope of a reef. A single colony can be golfball-sized or, after centuries of growth, five-10 yards in diameter. Corals build these structures, technically their skeletons, out of limestone that they secrete. They continually build up and expand their skeletons to fight erosion and compete with each other for sunlight.

Although corals are animals, not plants, sunlight is the key to their survival. They need it to power the millions of microscopic algae, called zooxanthellae, that live in their translucent tissues. The zooxanthellae provide the corals with food and oxygen in return for raw materials and a secure place to exist. This teamwork gives corals a competitive edge in nutrient-poor tropical seas, which are crystal-clear because they are low in algae and plankton that cloud more nutrient-rich waters. In hospitable conditions, corals can grow from just below sea level down to about 100 feet. At that point, the sunlight is too weak to energize the coral-zooxanthellae symbiosis.

Within the limited habitat of shallow, warm seas, any number of changes in the environment--from clouded waters to extreme water temperatures--can disrupt this relationship and lead to the decline of the reef. When stressed, the polyps expel their generally brownish zooxanthellae, exposing their white limestone skeletons through their translucent tissues. Without the algae, corals can not grow or reproduce. If the corals die, their skeletons--and eventually the reef--begin to erode.

Although this symbiotic relationship is the keystone of coral reefs, the entire ecosystem is much more than just a stand of corals. Coralline red algae encrust themselves in lime, cementing the actual reef together. Pieces of broken coral, mollusk shell, and other stony particles catch under the coral stands. Coralline algae grow over the top, strengthening the foundation. Parrot fish and sea urchins help with maintenance by chomping on the limestone with their powerful jaws, scouring off other algae that compete for space. In turn, they and other reef residents find shelter in the reef.

The chains of interdependence, extending throughout a reef, make the ecosystem resilient and productive. Reefs form the largest biological structures on the planet. The granddaddy of them all, Australia's Great Barrier Reef, may be between 500,000 and 2,500,000 years old and is said to be visible from the moon. Its high coral diversity corresponds with its great variety of reef fish and other organisms. Conversely, the destruction of both coral and other reef species can lead to the decline of both the diversity and the productivity of the entire ecosystem. Although 1,000 square yards of healthy reef might be able to feed 800 people, the same area, if degraded, is likely to support only one-quarter of that number or less.

Scientists only are beginning to understand the biological intricacies of reefs. No one knows for sure how many species live in coral reefs--or indeed in the oceans. In general, shallow waters have more species than deeper; rocky areas have more than sandy or muddy ones; and the tropics contain more than colder seas. Reef diversity also may increase with occasional disturbances, such as storms that level stands of corals or plagues of coral-eating predators that clean the reef of living tissue. As the corals recover through various stages of succession, more species may be able to find niches in the reef.

Human disturbances are harder on reefs than most natural disasters. People are thought to reduce diversity because they disrupt and destroy reefs too often for the corals to recuperate fully--through frequent visits by tourists, for example. The effects of pollution further can degrade reefs and inhibit rejuvenation. The reefs off Jamaica's north coast have not begun to recover from hurricanes in 1980 and 1988, as they would be expected to, apparently due to the impacts of overfishing and pollution. The once highly diverse, highly intricate reef there now is "flat" and dominated by algae.

Reefs on the rocks

For the 1992 International Symposium on Coral Reefs, Clive Wilkinson of the Australian Institute of Marine Science pulled together information from around the world on the status of this ecosystem. He estimates that, to date, people directly or indirectly have caused the death of five-10% of the world's living reefs and that, at current rates of destruction, another 60% could be lost in the next 20-40 years. His assessment did not include the potential effects of global warming and ozone depletion. Maintaining the general trend reef scientists have been documenting for more than two decades, the picture he paints is not an encouraging one--only reefs in remote regions are generally healthy. Although the combination of stresses and threats varies, reefs usually suffer from a mix of declining water quality, direct destruction, and depletion.

Areas with tracts of particularly devastated reefs include Japan, Taiwan, the Philippines, Indonesia, Singapore, Sri Lanka, and India in Asia; Kenya, Tanzania, Mozambique, and Madagascar in Africa; and the Dominican Republic, Haiti, Cuba, Jamaica, Trinidad and Tobago, and Florida in the Americas. The causes of degradation vary, but high coastal populations and heavy coastal development are factors shared by all.

Topping a long list of abuses against reefs is sedimentation from logging, farming, mining, dredging, and other coastal activities. Sediments that wash over reefs have a number of negative effects on corals. The initial plume blocks out sunlight, reducing zooxanthellae photosynthesis and therefore the quantity of energy available to the coral polyps. If the sediment settles on the reef, the polyps have to work together in waves to attempt to uncover themselves and produce extra quantities of mucus to try to wash off the particles. As a result, corals are weakened, have less energy for growing and reproducing, and are more vulnerable to disease. If the stress is too high, the corals will bleach and perhaps die. Sediments also impede coral larvae from forming new colonies on the reef.

Deforestation is the most common source of sediments, and mangrove clearing is the most important type of forest loss. Mangroves, which form along coastlines, trap soils that otherwise would wash into the coastal waters onto reefs. When trees are cleared, they no longer can play this protective role.

Coastal development, which helps drive this deforestation, is itself a major cause of reef decline. Sewage, industrial pollution, and urban runoff lower coastal water quality and harm reefs. Over half the world now lives in coastal regions and, as human numbers continue to grow, this proportion is expected to increase.

Coastal pollution does not always have immediate, obvious effects, but the steady influx of nutrients from soils and sewage, called eutrophication, gradually can cause the health of the reef to deteriorate. Initially, coral productivity increases with rising nutrient supplies. Then, as eutrophication progresses, seaweed and algae start to win out over corals for newly opened spaces on the reef because they grow more rapidly when fertilized. The normally clear waters cloud as phytoplankton begin to multiply, reducing the intensity of the sunlight reaching the corals, further lowering their ability to compete. At a certain point, nutrients in the surrounding waters begin to overfertilize the coral's own zooxanthellae, which multiply to toxic levels inside the polyps. Eutrophication may lead as well to black band and white band disease, two deadly coral disorders thought to be caused by algal infections. Through these stages of eutrophication, the health and diversity of reefs decline, potentially leading to death.

Mounting evidence suggests that the secondary effects of eutrophication may be as bad in some cases. Charles Birkeland, a reef scientist at the University of Guam, believes that nutrient flushes into coastal waters cause the outbreak of crown-of-thorns starfish, a coral predator that has plagued reefs from the Indian to the Pacific Ocean in recent decades.

Only reefs that are relatively untouched by human activity are in good shape. One of the better-off ones--Australia's Great Barrier Reef--is more than 160 miles from shore at its most distant point. Elsewhere, reefs usually are healthy along sparsely populated islands--particularly atolls, since soil runoff is limited.

Unfortunately for the reefs, people steadily are encroaching. In the Middle East, the lush reefs of the Red Sea contrast starkly with the surrounding desert landscapes. Until recently, this isolation had been the reefs' salvation since settlements along these bodies of water have been scarce and people living there have not used the reefs extensively for fishing or raw materials. With the oil boom, however, increased commerce has led to the degradation of some of the region's reefs. Oil spills can kill shallow corals outright, interrupt reproduction and metabolism, and smother corals if heavy tars settle. Even worse, detergents used to disperse spills are acutely toxic to corals, although new methods have been developed that avoid this problem.

Shipping is another serious threat to the Middle East reefs. In one case, a ship virtually eliminated all life on more than 500 square yards of reef when it ran aground and released several hundred tons of phosphate. Since the Iraq-Iran war, shipping through Al |Aqabah, Jordan, has intensified. The UN embargo of Iraq after its invasion of Kuwait has resulted in as many as 40 ships anchoring over the reefs at a time, waiting to get into the port. Similar damage from shipping and oil spills is found in the Caribbean, off the coast of southern India, and in parts of southeast Asia.

The many assets of reefs also are a reason for their decline. They attract people in pursuit of food, exotic species, gift-shop corals, and limestone for building materials, as well as tourists and tourist complexes. Although less insidious than sediment and other pollutants, overexploitation is a pervasive problem.

Reefs are also mined for building materials. In Sri Lanka and India, entire sections of reef have been removed to produce cement. People in island regions especially use the reef's limestone for construction, either because they have no other source of rock or because an island's base rock is volcanic, which is not strong or durable. Besides the direct destruction, removing large sections of reef can alter the water circulation and inhibit regrowth. This is particularly serious when dredged navigation channels allow lagoons to drain with the falling tide, exposing corals to the air.

Tourism often is cited as a motivation for countries to protect their reefs from these various forms of destruction, yet the boom in this industry is contributing to the degradation of reefs. In some instances, tourists and divers walk on the reef, killing coral polyps. Ellen McRae, a marine biologist in Belize, reports seeing dead patches of coral exactly the shape of snorkelers' fins. Reckless divers kick up sediments and break off pieces of corals. Although single incidents may be minor, the cumulative effect in heavily visited tourist centers, such as the Florida Keys, can be devastating.

Even if tourists stay out of the water, resorts built to serve them contribute to the degradation of coastal water quality. Beachfront development increases sedimentation of reefs, and hotels generally pipe their sewage and wastewater directly into the ocean, polluting nearby reefs. Moreover, they attract entrepreneurs who harvest corals and other souvenirs for local sale.

Ultimately, the forces behind reef decline are hard to untangle. Overexploitation and coastal pollution stem from business interests, wealthy consumers, the growing number of coastal poor, and governments trying to balance conflicting development goals. No single group is the cause of reefs' precipitous decline, yet all contribute to the tragedy.

In addition to the immediate threats of pollution and overuse, reefs will have to weather the future consequences of two forms of global environmental change--the gradual warming of the Earth due to the accumulation of carbon dioxide and other heat-trapping gases in the atmosphere, and the rising intensity of the sun's harmful ultraviolet rays due to the destruction of the stratospheric ozone layer by long-lived chlorofluorocarbons and other chemicals.

Many of the resulting changes are likely to harm coral reefs. Higher atmospheric carbon dioxide levels alone could chemically inhibit coral-building by the polyps. Stronger, more frequent storms increasingly would damage reefs. Despite general warming, major changes in ocean circulation would imperil reefs where cold or nutrient-laden waters replaced the more hospitable waters that now bathe them. Increased ultraviolet radiation already may be damaging corals in the shallow portions of reefs.

On their own, not all aspects of global warming would be damaging to corals and reefs. Healthy reefs can grow upward by as much as four inches per decade, faster than the predicted rate of sea level rise, and higher global temperatures could expand the range of reef-building corals beyond the tropics. In the course of centuries, corals even could adapt to changes in climate by colonizing new regions of the world or evolving to withstand higher water temperatures, as those in the Persian Gulf have done in order to survive summers there. Some scientists even hypothesize that bleaching may be the way corals adapt to warmer temperatures.

The outlook for coral reefs is made more dismal by their current situation. Rising sea levels alone would be a problem for polluted, abused reefs, which would not be able to grow as quickly as normal, if at all. Rising seas also would increase coastal erosion, potentially clogging the reefs with sediment, and, over the course of centuries, the rising tide could "drown" the reef by blocking out its sunlight.

At a minimum, global warming and ozone depletion are poised to further stress reefs that already are under enormous pressure from pollution and overuse. In addition, they are likely to harm reefs that have been isolated or protected until now.

Setting priorities

Coral reefs have surprised scientists with their rate of recovery once stress is relieved. The determining factors are the quality of the water and the supply of coral larvae to recolonize the reef. Where both water quality is good and plenty of larvae drift in from healthy reefs, scientists have found signs of recovery within a year, although it takes centuries to rebuild larger corals and missing sections of reef.

Thus, most coral reefs could begin to recover if governments pursued policies to protect and revive them. Currently, though, only a smattering of pilot projects and a few regional programs exist. The more common response is for a country to enact a few laws, which are not enforced or enforceable, and to designate a marine park or two, which may protect just a small section of reef or, worse yet, offer no funds or personnel for management. Governments rarely attempt to address the more basic issue of controlling land use and coastal development to prevent pollution of reefs.

To avoid continued reef decline in the decades ahead, countries need to pursue two areas of policy. One is the management and protection of reefs themselves; the other is pollution prevention. The basic tenants of reef management were developed over thousands of years by traditional cultures in the Pacific and Southeast Asia who relied on reefs for food. Out of necessity, they established conservation methods to ensure the long-term productivity of reefs. Typically, a master fisherman regulated use of the resource with closed seasons, size limits, species and area restrictions, quotas, and equipment regulations. This prevented overfishing and allowed reef species to repopulate the reef. Breaking the taboos against these restrictions could have led to expulsion from the community or death.

Modern centralized governments, however, have failed to safeguard and manage reefs. The few laws enacted to ban or regulate destructive fishing practices or coral removal are not enforced, either due to the lack of resources or a lack of will. Parks--the classic form of protection for natural habitats--largely are ineffective as traditionally designed. Although 65 countries worldwide have designated some 300 parks that include coral reefs, these are largely "paper parks," without the funds or staff to protect reefs sufficiently. In the Caribbean, which has the highest proportion of marine reserves, less than 30% of the designated areas are protected fully. Furthermore, in most countries, existing parks include only a small fraction of the reefs.

Australia broke the mold in 1975 when it created the Great Barrier Reef Park, although it is not a park in the traditional sense. The managers split the reef into sectors to satisfy various public demands. Some areas are restricted to scientific research, others allow tourists, and still others are open to commercial fishing and harvesting. The park authority monitors and regulates the use of the reef to try to ensure its health over the long term.

Marine scientists generally herald the Great Barrier Reef as the modern success story of reef management, but the approach used there does not transfer easily to developing countries. First, Third World governments do not have the resources to manage entire coastlines. Second, central management could conflict with local rights, as it has in the small sections of the reef aborigines traditionally used.

Local management holds greater promise in terms of both effectiveness and equity. In one example from the Philippines, university researchers convinced a local community to set aside a portion of the reef as an undisturbed breeding ground. The experiment led to a dramatic increase in the number of fish along the reef--so much so that outsiders wanted to fish there. Initially, the mayor of a nearby town overruled the restrictions and allowed commercial fishing, again depleting the reef. Eventually, the national government passed legislation to protect the local community's rights to the reserve.

Numerous communities in other countries similarly have demonstrated the value of locally managed fisheries. This approach draws on the lessons of traditional reef management. Given sufficient knowledge or training, local people are in the best position to manage the resource.

For this form of management to succeed, governments must provide legal backing for the community. Some island nations explicitly have traditional sea rights written into their constitutions. An alternative approach is to create a marine reserve in which the local community has control over the resources, as has been done at the Sian Ka'an Biosphere Reserve along the Caribbean coast of the Yucatan peninsula. Biospheres are managed for both conservation of the natural habitat and local use. UNESCO's Man and the Biosphere Program has established 10 biospheres worldwide that include coral reefs.

Stopping pollution

Conservation of the reef itself is vital, but not sufficient. Some of the sections of the Great Barrier Reef, for instance, are threatened by nutrients originating from the shore. Stopping coastal water pollution thus is a crucial piece of the policy puzzle.

Protecting coastal waters from pollution would offer many benefits beyond conserving reefs. Halting sedimentation would protect the land's topsoil, a precious commodity that requires centuries to form and one large rainstorm can wash away. Besides lowering the future productivity of agricultural and forest lands, soil erosion lowers the value of streams and rivers for drinking, irrigation, and fishing. Indiscriminate land clearing also can increase flooding and endanger people downstream.

Where coastal development occurs, cities can regulate industrial and municipal discharge into coastal waters to prevent damage to reefs. Controlling this form of coastal pollution would benefit not only reefs and other marine ecosystems, but public health as well. In some instances, beaches must be closed to tourists and fishers to guard against poisoning or the spread of disease. Insufficient sanitation facilities leads to the transmission of water-borne diseases, among the top killers of children in the developing world.

Reefs have been protected from eutrophication by centralizing waste and pumping it beyond the reefs. The classic example is Kaneohe Bay in Hawaii, where the city moved the sewage outfall beyond the reefs in 1979, and the ecosystem was on its way to recovery in a couple of years. This approach, however, is less than ideal--and illegal in some cases--if the waste is not treated.

Since the international community has a stake in the biological health of reefs, it has a role to play in their conservation. Growing recognition has prompted trade restrictions on corals under the Convention on International Trade in Endangered Species of Wild Flora and Fauna, and the United Nations now includes seven reefs in its World Heritage Sites. The World Bank plans to put 15-20% of its $3,000,000,000 biodiversity budget into marine and coastal habitats, and the U.S. Agency for International Development and other national governments are cooperating with Southeast Asian nations on the conservation of their reefs. If ratified and funded, the Convention of Biological Diversity signed by 153 governments at the Earth Summit in Rio de Janiero likely would supply money for the conservation of reefs as well.

The current rate of global environmental deterioration does not inspire hope that change will proceed rapidly enough to protect a significant portion of the world's reefs. For this reason, many marine scientists have come to think of the situation in terms of battlefield triage. Asked to compare the current conditions to the future threats of global warming, Guam University's Birkeland replied, "It's like walking into a doctor's office with a spear in your chest, and the doctor saying, |Let's see if you have a fever.'"

This sense of imminent loss has led some scientists to propose that the few undisturbed reefs should be protected before they too are damaged by expanding human activity. Robert Buddemeier, a reef scientist with the Kansas Geological Survey, suggests that island nations should receive compensation for setting aside remote or sparsely inhabited coral reef environments as permanent ecological preserves. He proposes that an international agreement could be developed along the lines of the Antarctic Treaty for the benefit of all.

However, protecting only a few reefs for future generations and allowing the rest to continue on their current path of decline would be a crime against nature and would make the world a much poorer place--aesthetically, biologically, economically, and culturally. Yet, as the general state of the global environment goes, so go the world's reefs. Ultimately, it is as much a question of whether we save or destroy the planet as it is a question of whether we save or destroy the world's reefs.

COPYRIGHT 1993 Society for the Advancement of Education
COPYRIGHT 2004 Gale Group