Thousands of fish, lobsters, sea turtles and other creatures live off the intricate reef structure. Coral reefs cover less than 1 percent of the ocean floor but support about 25 percent of all marine life, according to the International Coral Reef Information Network.

Reefs buffer shorelines from waves, helping prevent loss of life and property and protecting against erosion. Since they serve as habitat for fish and other marine species, they are vital to commercial fisheries and contribute about 25 percent of the food catch for developing nations, reports the National Oceanic and Atmospheric Administration.

Scientists are still just learning about reefs' potential benefits, including in the medical field, said Joe Pawlik, associate program officer in biological oceanography at the National Science Foundation.

Reefs "have a vast warehouse of various forms of life," he said, and from those animals and plants, drugs can be developed.

One of the most famous results from reef research is AZT, a treatment for those infected with HIV. An analysis of the chemicals from a Caribbean sponge provided vital clues to make AZT. Reef-related research has also helped in the advancement of treatments for cardiovascular diseases, skin cancer and leukemia and the use of bone grafting materials.

The benefits of coral reefs are also economic. A 2002 Global Coral Reef Monitoring Network report says reefs provide about $375 billion per year in goods and services to the world. In the Florida Keys alone, coral reefs create about $1.2 billion annually from tourism, such as diving tours, hotels, restaurants and other businesses, according to NOAA.

The largest coral reef in the world is the Great Barrier Reef in Australia, and the second largest is off the coast of Belize in Central America.

U.S. coral reefs cover about 6,500 square miles, 90 percent of which around U.S. islands in the Western Pacific and the rest off Florida, Texas and U.S. islands in the Caribbean. According to NOAA, about 27 percent of U.S. coral reefs are gone and another two-thirds will be lost within the next 30 years.

Causes of destruction

Coral reefs exist where land, sea and air meet, which can be a precarious spot. While reefs have evolved over hundreds of millions of years to cope with changes to the environment, recent evidence of a general decline shows stress factors may be outpacing reefs' recovery rate, according to a 2004 Pew Center on Global Climate Change report.

Usually located in shallow water, reefs near populated areas can be subject to factors such as nutrient loading from runoff, overfishing, destructive fishing practices such as using dynamite, damage from boats and nets, unintentional transportation of invasive species and the collection of coral.

Unusually warm ocean currents during El Nino and La Nina events can cause a phenomenon called coral bleaching. Scientists are concerned global climate change is contributing to this effect. Coral gets oxygen and nutrients from tiny algae, which also give the coral its color but are expelled under environmental stresses. Mass coral bleaching can occur when the water temperature rises. Smaller patches of bleaching can occur from chemical spills or increased sedimentation.

Scientists also are keeping an eye on how non-native species impact coral reefs. For example, the spiny and venomous lionfish, a native of the Indian and southwestern Pacific oceans, now lives off the coast of Florida and as far north as Long Island, N.Y., said Pawlik. The ravenous fish eats smaller fish, which could have a chain effect on reefs.

Satellite imagery, meanwhile, is used to track the path of dust kicked up from storms in Africa as the millions of tons of particles travel across the Atlantic to the Caribbean. Researchers now believe there may be a connection between the decline of Caribbean coral reefs and airborne pathogens.

The complexity of coral reefs and the chain of events that can lead to reefs' decline make it difficult to pinpoint sources of stresses. For example, Caribbean coral reefs used to be overrun by sea urchins, and briefly in 1982, sea urchins almost entirely disappeared off the coast of Puerto Rico, which caused pathogens to spread and prevented the recruitment of baby corals, said Pawlik. For unknown reasons, sea urchins are coming back and so are the baby corals, he said.

"Now people are wondering if this is the natural cycle," Pawlik explained, and if scientists are only observing part of the cycle.

Prevention of reef decline

Despite the difficulty in assigning causes to reef decline, NOAA and other organizations offer suggestions on how people can "save the reefs," such as not using chemically enhanced pesticides and fertilizers, not leaving garbage on beaches and conserving water to cut back on wastewater that makes it back into the ocean.

Other NOAA recommendations include anchoring boats on buoys instead of reefs, reporting illegal dumping and when diving, avoiding touching coral animals or stirring up sediment that can settle on the coral and smother it.

A U.S. Coral Reef Task Force is working on mapping and assessing the condition of coral reefs in the Pacific, establishing coral reef protected areas, creating a monitoring system, coordinating federal, state, territory and other partners to restore injured coral reefs and strengthening local efforts to protect reefs.

The task force, established in June 1998, is made up of NOAA, the Agriculture, Interior, Transportation, Justice, State and Defense departments, Environmental Protection Agency, National Science Foundation and National Aeronautics and Space Administration. They work with the governors of seven states, territories and commonwealths responsible for coral reefs.

In March 2000, the task force set up 13 goals to understand and reduce adverse impacts on coral reefs, including designating 20 percent of U.S. coral reefs as "no-take ecological reserves"; mapping all U.S. coral reefs by 2009; building a national reef monitoring system to track reef health; and funding coral reef management priorities in U.S. islands.

When the task force began, only about 10 percent of the hundreds of thousands of square miles of coral reefs were mapped and characterized, said Roger Griffis, the coordinator of NOAA's Coral Reef Conservation Program. The task force is more than halfway through the mapping process and expects to finish before its 2009 deadline, he said.

In addition, satellite-based observation systems are helping researchers understand how and why coral reefs die, and enable them to forecast incidents of coral bleaching, said Griffis. When coral reef managers receive bleaching warnings, they can adjust reef uses to reduce certain stresses and make reefs less susceptible to bleaching, he said. The alert system also raises public awareness about the health of reefs, he added.

In 2002, the task force called for the development of "local action strategies" to address six key threats to coral reefs: land-based pollution, overfishing, lack of public awareness, recreation overuse and misuse, climate change and coral bleaching, and disease, Griffis said. Coordinating the local-level efforts enables the pooling of technical and financial resources, according to the task force.

On an international level, the Convention on the International Trade in Endangered Fauna and Flora, or CITES, is a treaty that regulates trade in coral. Certain types of coral are classified as Appendix II species under CITES, which means they are not necessarily threatened with extinction but may become so unless their trade is strictly controlled.

The Global Coral Reef Monitoring Network, made up of dozens of nations, non-governmental organizations, multilateral development banks and private sector interests, works to raise awareness about coral reefs and promote their protection and sustainable use.

Editor's Note: The NewsHour's Science Unit is funded by the National Science Foundation.

-- By Larisa Epatko, Online NewsHour