Coral reefs help keep the Earth’s biosphere, the part of the planet where living things are found, in balance. One of the coral reef’s important functions is in maintaining normal levels of carbon dioxide in the atmosphere. At the point where the atmosphere meets the sea, carbon dioxide and other gases from the air dissolve in ocean water. In places where coral reefs exist, much of this dissolved carbon dioxide is removed from the water by coral organisms. The organisms then use the gas to build calcium carbonate, or limestone, skeletons. As the skeleton-building proceeds, levels of the dissolved gas in ocean water decrease, permitting more carbon dioxide to enter the water from the atmosphere. For this reason, reefs act as carbon “sinks.”
Carbon dioxide is one of several so-called greenhouse gases that form an invisible layer around the Earth. As shown in Figure greenhouse gases trap the Sun’s heat near the Earth’s surface, very much like the windows in a greenhouse hold in heat from the Sun. The greenhouse gases are one of the reasons that temperatures on Earth’s surface are warm enough to support life. If they did not exist in the atmosphere, most of the Sun’s radiant energy would bounce off the Earth’s surface and return to space.
The layer of greenhouse gases is changing, however, and this change has many scientists worried. By burning fossil fuels in homes, cars, and industries, people all over the world are constantly adding carbon dioxide to the air, widening the belt of greenhouse gases. Many environmentalists fear that the rising levels of carbon dioxide in the air are warming the Earth’s surface abnormally, a phenomenon known as global warming.
Research indicates that some warming has already taken place in the air and in the ocean. The effects of this warming include less snow cover each winter, a retreat of mountain glaciers, and changes in global weather patterns. Experts fear that continued warming could damage the balance of life on Earth. Some predict far-reaching results, including changes in climates, melting of glacial ice, and damage to the coral reefs.
|Carbon dioxide is one of the|
greenhouse gases in the atmosphere that traps
heat close to the surface of the Earth.
Coral reefs are usually found near coastlines. Because of their positions in relation to landmasses, some of them form natural, protective walls for coasts. The walls act as fortresses, diminishing the destructive forces of the waves as they pound the shore during storms or times of high tides. These reef walls also help prevent erosion, damage to coastal sea life, loss of property, and even loss of human life. Without the coral reefs, the homes and businesses of millions of people would be exposed to the full fury of the sea. About one-sixth of the world’s shores are protected by reefs. Some of these areas, such as the coasts in Asia, support the densest populations of humans in the world.
Coral reefs also contribute to beach formation. Natural forces break off pieces of the reef and grind them into grains of sand. As wind and water strike the reef, they chip away at the skeletal structures of reef animals, eroding them into small pieces. Predators also loosen reef material by nibbling on it to get at choice foods. Even some of the plants and animals that grow on reefs erode them. Once dislodged, small particles of reef are tossed and crushed by waves until they form fine particles of sand. Beaches created primarily by erosion of coral are brilliantly white. Barbados, an island in the West Indies, is one of hundreds of islands built on coral and famous for its prized white beaches.