OCEANS Are on the Critical List.

• Author: MCGINN, ANNE PLATT

The primary threats to the planet's seas--overfishing, habitat degradation, pollution, introduction of alien species, and climate change--are largely human-induced.

OCEANS FUNCTION as a source of food and fuel, a means of trade and commerce, and a base for cities and tourism. Worldwide, people obtain much of their animal protein from fish. Ocean-based deposits meet one-fourth of the world's annual oil and gas needs, and more than half of world trade travels by ship. More important than these economic figures, however, is the fact that humans depend on oceans for life itself. Harboring a greater variety of animal body types (phyla) than terrestrial systems and supplying more than half of the planet's ecological goods and services, the oceans play a commanding role in the Earth's balance of life.

Due to their large physical volume and density, oceans absorb, store, and transport vast quantities of heat, water, and nutrients. The oceans store about 1,000 times more heat than the atmosphere does, for example. Through processes such as evaporation and photosynthesis, marine systems and species help regulate the climate, maintain a livable atmosphere, convert solar energy into food, and break down natural wastes. The value of these "free" services far surpasses that of ocean-based industries. Coral reefs alone, for instance, are estimated to be worth $375,000,000,000 annually by providing fish, medicines, tourism revenues, and coastal protection for more than 100 countries.

Despite the importance of healthy oceans to our economy and well-being, we have pushed the world's oceans perilously close to--and in some cases past--their natural limits. The warning signs are clear. The share of overexploited marine fish species jumped from almost none in 1950 to 35% in 1996, with an additional 25% nearing full exploitation. More than half of the world's coastlines and 60% of the coral reefs are threatened by human activities, including intensive coastal development, pollution, and overfishing.

In January, 1998, as the United Nations was launching the Year of the Ocean, more than 1,600 marine scientists, fishery biologists, conservationists, and oceanographers from across the globe issued a joint statement entitled "Troubled Waters." They agreed that the most pressing threats to ocean health are human-induced, including species overexploitation, habitat degradation, pollution, introduction of alien species, and climate change. The impacts of these five threats are exacerbated by poorly planned commercial activities and coastal population growth.

Yet, many people still consider the oceans as not only inexhaustible, but immune to human interference. Because scientists just recently have begun to piece together how ocean systems work, society has yet to appreciate--much less protect--the wealth of oceans in its entirety. Indeed, current courses of action are rapidly undermining this wealth.

Nearly 1,000,000,000 people, predominantly in Asia, rely on fish for at least 30% of their animal protein supply. Most of these fish come from oceans, but with increasing frequency they are cultured on farms rather than captured in the wild. Aquaculture, based on the traditional Asian practice of raising fish in ponds, constitutes one of the fastest-growing sectors in world food production.

In addition to harvesting food from the sea, people have traditionally relied on oceans as a transportation route. Sea trade currently is dominated by multinational companies that are more influenced by the rise and fall of stock prices than by the tides and trade winds. Modern fishing trawlers, oil tankers, aircraft carriers, and container ships follow a path set by electronic beams, satellites, and computers.

Society derives a substantial portion of energy and fuel from the sea--a trend that was virtually unthinkable a century ago. In an age of falling trade barriers and mounting pressures on land-based resources, new ocean-based industries such as tidal and thermal energy production promise to become even more vital to the workings of the world economy. Having increased sixfold between 1955 and 1995, the volume of international trade is expected to triple again by 2020, according to the U.S. National Oceanographic and Atmospheric Administration, and 90% of it is expected to move by ocean.

In contrast to familiar fishing grounds and sea passageways, the depths of the ocean were long believed to be a vast wasteland that was inhospitable, if not completely devoid of life. Since the first deployment of submersibles in the 1930s and more advanced underwater acoustics and pressure chambers in the 1960s, scientific and commercial exploration has helped illuminate life in the deep sea and the geological history of the ancient ocean. Mining for sand, gravel, coral, and minerals (including sulfur and, most recently, petroleum) has taken place in shallow waters and continental shelves for decades, although offshore mining is severely restricted in some national waters.

Isolated, but highly concentrated, deep-sea deposits of manganese, gold, nickel, and copper, first discovered in the late 1970s, continue to tempt investors. These valuable nodules have proved technologically difficult and expensive to extract, given the extreme pressures and depths of their location. An international compromise on the deep seabed mining provisions of the Law of the Sea in 1994 has opened the way to some mining in international waters, but it appears unlikely to lead to much as long as mineral prices remain low, demand is largely met from the land, and the cost of underwater operations remains prohibitively high.

Perhaps more valuable than the mineral wealth in oceans are still-undiscovered living resources--new forms of life, potential medicines...