It comes down to the coasts.

ALONG THE SEAMS OF THE EARTH WHERE LAND MEETS SEA, BIOLOGICAL PRODUCTIVITY IS MUCH HIGHER THAN FOR THE REST OF THE PLANET'S SURFACE. IF THE COASTS ARE TO CONTINUE SERVING THEIR ESSENTIAL ECOLOGICAL AND ECONOMIC FUNCTIONS, WE WILL HAVE TO BEGIN ALTERING OUR PATTERNS OF HUMAN SETTLEMENT AND DEVELOPMENT.

What is a view of the ocean worth? The price of a night at an expensive hotel, or the purchase of a beachfront bungalow? Enduring a biting winter wind, or a beach-bound traffic jam on a sultry day in August? For many, the answer is: whatever it takes. Every year, half of the world's vacationers head for the sea. But for many more people, being close to the shore is worth something more than an annual pilgrimage. It is worth the cost of leaving better-paying jobs, or ancestral ties, or friends--and moving their homes to the coast. Fully half the world's people live within 50 miles or so of saltwater. And their ranks are growing. In 30 years, the same number of people as are now on earth--some 5.5 billion--are expected to live in the coastal zone.

What is the attraction? The meeting of land and sea works a kind of magic that is more powerful than that of just scenic beauty. The soil on the coastal plain, laid down when the land was covered by the ocean, and subsequently replenished by sediments washed down from the mountains, tends to be particularly fertile. About 2 percent of the world's agricultural land, including some of its most intensively and productively cultivated land, was actually taken from the sea by people.

Offshore, the same nutrients promote the growth of aquatic plants, which in turn feed fish that now provide humankind's largest single source of animal protein--larger, even, than beef or chicken. The world's primary fishing grounds are in these fertile coastal waters, from which 90 percent of the marine catch is taken (see map on pages 24-25). Farming and fishing are major coastal industries that employ hundreds of millions of people worldwide.

Coastal dwellers can also make a good living from international trade, 80 percent of which is carried by ship. That's one reason why nine of the world's 10 largest cities and 33 of the top 50 are near the coasts. And of course there are the vacationers bringing their portion of the $1.9 trillion annually spent on tourism worldwide. Although there are no estimates for coastal tourism alone, the Madrid-based World Tourism Organization estimates that tourism accounts for nearly one-tenth of the global economic output and is one of the fastest growing industries. The attraction of the coasts is as much economic as aesthetic. It's not surprising, then, that the narrow ribbons of land and water that outline the world's continents and islands are widely used as development zones. The phenomenon is nowhere more vividly illustrated than in The Netherlands, whose crowded populace lives with the sea literally in its back yard. In fact, one-third of The Netherlands is land that used to be under the North Sea or its tributaries; because coastal land is so valuable to the Dutch, they have been diking and draining it continuously for over a thousand years. Their sea-hugging cities are now thriving centers of commerce and culture, and their farms are some of the most productive in the world.

All this activity may churn out money, but it is also churning up the coasts--as the Dutch have become acutely aware in recent decades. Draining wetlands has reduced the natural habitat for wildlife and has driven the Dutch national symbol, the stork, from the country (see cover story in the January/February World Watch).

But the problem is more than just a few endangered species. By choosing to concentrate its swelling population along the coasts, humanity is locating the ecological damage of its activities precisely where the world's most productive ecosystems are concentrated. The coastal zone, extending from the beginning of the coastal plain to the end of the continental shelf, accounts for only 8 percent of the world's surface area, but hosts 26 percent of the earth's primary (plant) productivity, the world's major spawning and nursery grounds, and one of the earth's most diverse ecosystems, the coral reefs. As a result, coastal areas, which are approximately twice as productive on average as the inland areas, suffer roughly nine times more damage because of the number of people living there.

HAZARDS AT THE CROSSROADS

Having chosen to live where land meets sea, humanity has greatly increased the difficulty of achieving a stable relationship with the Earth's environment. The intersection between human and biological activity has already scarred the coastal landscape by altering and destroying large portions of some of its most fertile habitat.

Not all coastal habitat is highly productive; about half of the world's 440,000 kilometers of coastline are lined by cliffs and ice, and another 20 percent are beaches, which have relatively low biological activity. However, wetlands and estuaries, where rivers turn brackish as they enter the sea, are among the most productive of all ecosystems. There, nutrients from land feed plant growth so abundant that mangrove forests, for instance, which cover only 0.4 percent of the world's surface area, account for 2.3 percent of plant productivity. That fecundity makes mangroves, other coastal wetlands, and estuaries particularly important as nurseries for marine species. Some two-thirds of all commercially caught fish spend their first and most vulnerable stages in estuaries and wetlands, and many more species go to these coastal ecosystems to feed. These are also some of the most endangered ecosystems in the world. Estuaries are particularly vulnerable because they are naturally sheltered harbors, and therefore tend to be heavily used and polluted. Wetlands have traditionally been regarded as wasteland, and therefore are targets for city expansion. All over the world, there are coastal cities that have degraded nearby estuaries and wetlands through the combined effects of direct habitat destruction and pollution. Commercially burgeoning Singapore, for example, has removed almost all of its mangrove wetlands and reduced offshore water visibility from eight meters prior to 1960 to an average three meters in 1992. San Francisco Bay, the largest estuary in the western United States, has lost 60 percent of its water area to land reclamation over the past 140 years.

It is agriculture, however, not urbanization, that causes the most extensive destruction. The Dutch impound coastal wetlands with dikes, then pump them dry with windmills, primarily for the fertile farmland. The Chinese have been draining coastal wetlands for the rich soils they yield for 6,000 years. The densely populated delta country of Bangladesh has impounded at least 30,000 square kilometers of wetland for agriculture; it is no coincidence that Bangladesh has the world's highest population density for a mainland country, as well as the largest area of impounded farmland.

Other causes of extensive coastal habitat destruction include the rapidly expanding fish farming industry, timber extraction, and civil engineering projects that alter the flow of sediments and fresh water. The wetlands at the mouth of the Mississippi River are eroding away at a rate of 150 square kilometers per year, largely due to flood control and channeling projects in the delta and upstream. Worldwide, about half of all saltmarshes and mangrove swamps have been cleared, drained, diked, or filled, and few estuaries remain unpolluted or unaltered.

Offshore, coral reefs, kelp forests, seagrass beds, and other shallow water habitats are endangered by the combination of direct destruction and pollution from land. Coral reefs are of particular concern. They line more than 100,000 kilometers of coast and harbor a large portion of the coasts' biological wealth. Unfortunately, they are highly vulnerable to changes in their environment. If the normally clear tropical waters they form in are clouded by pollutants, for example, the corals can't photosynthesize to produce their food. They also recover slowly when damaged. Other offshore habitats, likewise, suffer from such habitat degradation. The pollution and harbor development off Singapore, for instance, has degraded the majority of the seagrass beds and all but 5 percent of the coral reefs.

The unique ecology of coral reefs makes them one of the world's most diverse ecosystems, second in density of unique species only to tropical rain forests; thus the widespread damage to these reefs constitutes a major blow to the Earth's overall biological diversity. Yet, 5 to 10 percent of the planet's coral reefs have essentially been ruined by pollution and direct destruction, and another 30 percent could be lost in the next 10 to 20 years. The most graphic examples are the extensive portions of reef that have been mined for construction materials in places like southern India and Sri Lanka, and the damage caused by fishers using explosives to kill and catch fish. But globally, pollution from burgeoning developments onshore is the more extensive and intractable threat to these and other coastal habitats.

THE DEMOGRAPHIC SQUEEZE

Without closer attention to the management and protection of these coastal ecosystems, the destruction is bound to accelerate. Because of steady coastward migration, coastal populations--and the environmental pressures they bring--may be growing even faster than the global population, which is climbing by some 90 million people a year.

One of the forces driving the trend is rural poverty. Like a pied piper, the promise of employment in cities draws people from depressed agricultural areas. The United Nations estimates that 20 to 30 million of the world's poorest people annually migrate from rural to urban areas, especially to Third World mega-cities, which are usually on the coasts. Rural coastal populations may also be increasing for similar reasons. In the Philippines, the coastal population is growing faster than that of the rest of the country in part because people who give up on farming often move to coastal areas to try fishing. While land is scarce, open access to fishing grounds gives poor people at least the hope of making a living.

In China, the coastal population may be increasing by 10 percent or more per year, though the country's overall growth rate is only 1.2 percent. Already the population density along the China coast is three times as high as the national average, and this region accounts for 70 percent of the country's gross national product. While the economic success along the coast will inevitably attract more Chinese, the government is encouraging this coastward migration by placing special economic development zones there.

In Southeast Asia, where marine biodiversity is particularly high, more than two-thirds of the population lives within the coastal zone. Coastal populations are also particularly high in southern Asia, Europe, southeastern Africa, and portions of North and South America. And as the global trend of rural flight and urbanization progresses, the challenge to protect the world's coasts will become more severe.

MORE THAN COASTAL LIVING

As if this pattern of human habitation weren't damaging enough, the thin ribbons of coast are also subject to devastating environmental assaults from both far inland and out at sea. Pollution from human activity outside of the coastal zone funnels into estuaries and coastal waters, while in an almost mirror image, the impacts of fishing and shipping become more concentrated closer to shore. A surprising proportion of the pollutants entering coastal waters originates not from the adjacent coastal land but from more distant sources. Of the polluting nutrients, about half come from inland. In the eastern United States, for instance, the Chesapeake Bay has been overwhelmed by nutrients from inland sources. Farms contribute one-third and air pollution another one-quarter of the nitrogen pollution that has caused eutrophication, algal blooms, and oxygen depletion in this estuary--once one of the most productive in the world. The oyster catch in the Chesapeake has fallen from 20,000 tons in the 1950s to under 3,000 tons in the late 1980s, at least partly as a result of this pollution. In a study of samples from 42 of the world's major rivers, Jonathan J. Cole and his colleagues at the Institute of Ecosystem Studies at the New York Botanical Garden found that the level of pollution correlates uncannily with the level of human activity in the watershed. The Rhine, for example, has 10 times the population density of the Mississippi, and dumps 10 times more nutrients into the sea, even though the Mississippi drains an area 14 times as large. About one-third of the pollutants entering the marine environment come from air emissions, a large portion of which settle into coastal waters. For many heavy metals and volatile organic chemicals, air is the primary route to the sea. In the North Sea, about a quarter of the pollution, including the majority of PCBs and other chlorinated organic chemicals, comes from the air. In the Persian Gulf, the 4 to 12 million barrels of oil that the Iraqi army deliberately spilled during the 1991 Gulf War turned out to be only part of the total amount of oil estimated to have entered the Gulf as a result of the war. Another 4 to 5 million barrels are thought to have been carried into the Gulf by oil-laden smoke. Worldwide, about 10 percent of the oil that reaches the oceans is airborne.

Ironically, human industries and settlements are choking coastal waters with the very rivers that make these waters productive. The excess nutrients, sediments, pathogens, and persistent toxins come mostly from land-based sources. Even oil pollution, which is typically associated with accidents at sea such as that of the Exxon Valdez, is as likely to have flowed into the water directly from a car or factory on land as from a barge or boat.

On the ocean side of the coastal zone, overfishing has depleted some of the world's major fish stocks, along with the health of their ecosystems. There is a growing crisis in the world fisheries, as epitomized by the collapse of North Atlantic cod stocks off Canada. Although pollution and habitat destruction have played a role in this crisis, the main problem is simply that the capacity of the fishing industry--in numbers of people and in the efficiency of their high-tech equipment--has grown too large for the regenerative capacity of the oceans. Of the world's 17 major fishing grounds, all of which are primarily coastal, every one has been fished to its limits or beyond, according to the United Nations Food and Agriculture Organization (FAO), which tracks global fishing trends. Nine are now in serious decline because of overfishing. As high-tech factory boats and traditional fishers alike have extracted larger and larger proportions of the biomass from coastal waters, whole ecosystems have begun to break down. In the Shetland Islands, Arctic terns, puffins, and other nesting birds failed to breed in the mid- and late 1980s, apparently due to overfishing of the sand eel, a small shoaling fish caught for fish meal and oil. The birds normally feed young sand eels to their chicks, but the fish's population declined with the commercial catch, which peaked at 56,000 tons in 1982 and then plunged to 4,800 tons in 1988. In a similar disaster, off the coast of Peru, guano birds abandoned their young when the Peruvian anchovy fishery collapsed. In Kenya, researchers found that heavy fishing of triggerfish on coral reefs allowed the proliferation of rockboring sea urchins, which were endangering the entire ecosystem.

GLOBAL IMPLICATIONS

What happens to the coasts has effects that reach far beyond their local aquatic and human communities, however. Though they are among the most vulnerable of Earth's ecosystems, the coasts house biological processes and diversity that are essential to the health and stability of the biosphere as a whole. The oceans, which are the largest ecosystems, rely disproportionately on the coasts for food. Although the coastal waters over continental shelves cover only 10 percent of the ocean surface, they account for 20 percent of the marine plant production. The energy captured in these waters' prolific plant growth feeds into the oceanic food chain, starting with small marine organisms such as copepods and other zooplankton, and moving out to sea with currents and migratory species. Unlike on land, animal life makes up the majority of biomass in the oceans, and its movement into the open ocean redistributes some of the disproportionate productivity of coastal waters.

This coastal productivity also helps to drive the oceans' "biological pump," the process by which the oceans help to regulate global climate. Scientists have found that the marine food chain moderates the atmospheric concentration of carbon dioxide, the primary heat-trapping gas. Carbon dioxide enters the churning upper layer of the oceans, where phytoplankton and other marine plants use it in photosynthesis to make simple sugars. While 90 percent of this carbon is recycled through the food chain, some falls into the deeper layers of the oceans as the detritus of decaying phytoplankton and other sea plants or animals. There, the carbon is stored in deep ocean currents that take about 1,000 years to bring it back to the surface as carbon dioxide.

The large amounts of biomass produced and consumed along the coasts, too, may play a major role in global warming. On one hand, some of the carbon dioxide captured by marine plants is stored in coastal sediments. On the other hand, some of the carbon trapped in organic matter flowing in from land is oxidized and rereleased to the atmosphere. Scientists are still uncertain whether the coasts are a net source or sink of carbon. But either way, altering coastal processes is likely to have a global impact because of the sheer quantity of carbon pumped through this zone.

The high biological diversity of the coasts helps to stabilize these global systems. Organisms ranging from bacteria to great blue whales play key roles. Copepods, for instance, are minute crustaceans that eat phytoplankton and are thought to be the most numerous animals in the oceans. They fill a critical link between the primary producers and the rest of the marine food chain. If ecological conditions change in a way that no longer permits copepods to perform this function, their disappearance could have devastating consequences. But there's another dimension, as well, to the extraordinary diversity of coastal organisms. About 90 percent of the history of life on earth has taken place in salt water, making the oceanic gene pool an invaluable resource. Its species are the descendants of the 3 to 3.5 billion years of evolution that predated the appearance of plant life on dry land some 450 million years ago. Therefore, many coastal species have no evolutionary counterparts on dry land. These unique species make irreplaceable contributions to food production, medicine, and scientific research.

A large proportion of these species are housed in coral reefs. Only the deep ocean floor, which covers half the earth's surface, is thought to contain more. Within coastal waters, a general rule of diversity is that shallow waters harbor more diversity than deeper waters, rocky areas more than sandy or muddy ones, and the tropics more than temperate or polar zones. Coral reefs--shallow, rocky, and tropical--are believed to contain the highest density of unique species in the oceans.

Researchers are increasingly turning to these coastal waters in their search for medical cures and unique compounds. They have derived anti-leukemia drugs from sea sponges, bone graft material from corals, diagnostic chemicals from red algae, and anti-infection compounds from shark skin. Because marine life is relatively unstudied compared to terrestrial life, the oceans and coasts are a vast new frontier for research.

SHORING UP THE SEA

Under the current international regime, protecting the coastal zone is up to coastal nations. Nearly two decades ago, international negotiations over the Law of the Sea, a United Nations-mediated treaty on the management of the oceans, gave rise to international acceptance of the concept of a 200-nautical-mile coastal area--called the Exclusive Economic Zone (EEZ)--within which the coastal country has exclusive rights to the natural resources. By 1976, 60 countries had claimed EEZs of their own and the notion became an accepted part of customary oceans law.

The recent ratification of the Law of the Sea formalizes the EEZ construct and puts in force the treaty provisions that encourage coastal states to conserve and protect these waters. But the language is vague and probably unenforceable because of long-standing concerns over national sovereignty--the same issue that blocked international standards for coastal zone management at the 1992 Earth Summit in Rio de Janeiro. The delegates acknowledged the growing coastal crisis, but they shied away from infringing on national jurisdiction.

Of the three major threats to the coasts--coastal development, pollution from inland, and overfishing of coastal waters--it is development that warrants the highest priority for major changes in policy. The direct destruction and pollution of essential ecosystems is steadily undermining the coastal zone on every continent, and the surging of coastal populations means that these threats are worsening.

The single most effective change that could be made to slow the juggernaut of coastal development would be to eliminate subsidies such as government-sponsored insurance and funding for ocean-altering roads, dikes, and dams. The Netherlands, for instance, spends $400 million a year just to pump water and repair inland dikes, and new seawalls and dikes can cost hundreds of millions of dollars. These investments have come under domestic scrutiny, not only because they contribute to the loss of coastal habitat for the stork and other wetland-dependent species, but also because they may not be cost-effective. Some of the impounded agricultural land is often too wet to farm, and the Dutch don't need all of it because they are already producing more food than they can either use of sell abroad. As a result, expenditures on draining coastal land for farming can lead, absurdly, to still more expenditures on farm subsidies to cover excess production.

To save money and begin rehabilitating the coastal ecosystem, the Dutch government has made an extraordinary and courageous decision to return 150,000 hectares of farmland (15 percent of the total converted area) to rivers and estuaries over the next 25 years. Although the Dutch will continue diking and developing other parts of the coastal zone, this reversal reflects their growing concern over the degradation of their coasts.

In the early 1900s, the Dutch built a 30-kilometer-long earthen seawall across the mouth of the Zuider Sea in the northwest to protect the impounded farmland in the estuary from flooding. The barrier against the sea completely altered the original ecosystem, turning the giant brackish water estuary into a fresh water lake, now known as Lake IJssel. The country has continued to pursue this strategy of "coastal defense," but recent projects have been more ecologically sensitive. For instance, rather than building a similar earthen seawall across all of the estuaries in the rich coastal region of Zeeland in the southwest, the Dutch built mechanical seawalls that can be opened to allow relatively natural water flow, and closed in case of a strong coastal storm that threatens flooding.

As the Zeeland projects demonstrate, coastal development can be made less destructive. But the methods don't have to be high-tech engineering solutions. Natural buffer zones, for instance, can protect coastal habitat from nearby development. Wetlands trap toxins, pathogens, and excess nutrients and sediments as they move seaward, while also protecting coastal communities from coastal storms and sea surges. Coral reefs act as natural seawalls, reducing the erosive action of the ocean by absorbing the impact of waves.

Simple guidelines can make a significant difference. In Thailand's Ban Don Bay, for instance, the provincial government instituted building restrictions to protect the region's primary tourist attraction, the coral reefs. Developers now must build back from the beach and cannot use coral for construction material. In Ecuador, which has lost 144,000 hectares of mangrove forests to shrimp ponds, the government is sponsoring a national program to manage coastal resources so that local communities can continue to profit from them without destroying them. Starting with a U.S. Agency for International Development pilot project, the Ecuadorean government has formed six special coastal management zones, with management committees composed of local and government people. In the case of the shrimp industry, which constitutes a sizable portion of Ecuador's exports and economy (nearly 80,000 metric tons of shrimp, worth almost $500 million in 1991), shrimp farmers were given special training on how to protect the coastal environment while maintaining their livelihoods. Even if well-managed, however, coastal development could turn the world's coastlines into continuous strings of cities, farms, and resorts. Aside from the catastrophic ecological impacts, such an eventuality could take a heavy toll on those who live and invest there. As is becoming increasingly evident in places like the Eastern seaboard of the United States, coasts are dynamic. Portions are always eroding or shifting, and over the course of tens of thousands of years, changes in sea level can alternately expose and inundate the coastal zone. In the 10,000 years since the last ice age, the sea level has been rising as the result of melting ice and glaciers and thermal expansion of the oceans. Most of the world's low coasts continue to retreat due to the recent rate of sea level rise of 1 to 2 millimeters per year, or 10 to 20 centimeters per century. With the increase in greenhouse gases and the threat of global warming, coastal living in the coming century will become more precarious. Sea level is projected to rise by 60 centimeters in the next 100 years, and storms are likely to grow stronger. Governments may need to consider restricting or even prohibiting further coastal development altogether.

Peter Weber is a research associate at the Worldwatch Institute. He is author of Worldwatch Paper 116, Abandoned Seas: Reversing the Decline of the Oceans (1993), and co-author of State of the World 1994. This article based on field research in the Netherlands, as well as on his previous work on the subject and on the sources listed below.

KEY SOURCES

Fan Zhijie and R.P. Cote, "Population, development and marine pollution in China," Marine Policy, May 1991.

P.M. Holligan and H. de Boois eds., Land-Ocean Interactions in the Coastal Zone, The International Geosphere-Biosphere Programme: A Study of Global Change of the International Council of Scientific Unions, Stockholm, February 1993. Joint Group of Experts on the Scientific Aspects of the Marine Pollution (GESAMP): The State of the Marine Environment, UNEP Regional Seas Reports and Studies No. 115 (Nairobi: United Nations Environment Programme, 1990).

United Nations Food and Agriculture Organization, Marine Fisheries and the Law of the Sea: A Decade of Change, FAO Fisheries Circular No. 853, Rome, 1993.

H. Jesse Walker, "The Coastal Zone" in B.L. Turner II et al., The Earth as Transformed by Human Action (New York: Cambridge University Press, 1990).