Coral Reefs

Coral Reefs

Coral reef is a type of underwater environment shaped by limestone formations. Reef limestone consists largely of a framework of skeletons from marine animals called corals. Reefs also contain the remains of other limestone-producing organisms, such as algae and shellfish, as well as sand and other particles. A coral reef is a complex, biologically rich ecosystem. Many of the world's most colorful animals live in coral reefs. Reefs also provide important benefits to people and to the larger environment.

Coral animals produce formations that may resemble branching trees, large domes, small irregular crusts, or tiny organ pipes. They can glow with rich colors, including beautiful shades of green, orange, purple, tan, and yellow. Coral limestone resists damage from waves, and it can grow hundreds of yards or meters thick. Overall, coral reefs range widely in area. Small patch reefs measure only a few square yards or meters, while some interconnected reef systems span hundreds of square miles or kilometers.

Kinds of coral reefs.

There are three basic types of coral reefs: fringing reefs, barrier reefs, and atolls. Fringing reefs lie close to shore. They usually are younger, and thus smaller, than barrier reefs or atoll reefs. Barrier reefs also follow the contours of the shore, but they occur farther from the coast than do fringing reefs. Barrier reefs form a barrier between a body of water near the shore, called a lagoon, and the open sea. Barrier reefs may consist of one fairly continuous reef, or they may be made up of a series of reefs separated by open water channels.

Some barrier reefs grow to a considerable size. Australia's Great Barrier Reef ranks as the largest group of coral reefs in the world, measuring about 1,240 miles (2,000 kilometers) long.

Atolls are ring-shaped reefs that often create coral islands in the open sea. An atoll forms as an old water-bound volcano slowly sinks into the sea, or the sea level rises around it. The reef grows upward from the surface of the volcano's rim and creates a large ring that surrounds a lagoon. One or more channels connect the lagoon to the open sea. Many coral islands of the South Pacific Ocean are atolls.

Where coral reefs exist.

Coral reefs lie mainly in shallow tropical or subtropical seas. Most reef-forming corals cannot live in water colder than 61 to 68 °F (16 to 20 °C). Reefs require enough sunlight to support photosynthesis in their algae and plants. Photosynthesis is the process in which organisms use energy from sunlight to make food.

Coral reefs occur throughout warm waters of the Pacific Ocean, in coastal waters of Southeast Asia, in the Indian Ocean as far north as Sri Lanka, around Madagascar on the southeast African coast, and in the Red Sea. They also form along the tropical eastern coast of Brazil, in the Caribbean Sea, and along the coasts of Florida and Bermuda. Though coral reefs do not develop in colder seas, certain corals live as far north as the Arctic Circle.

Life on coral reefs.

Tens of thousands of living species inhabit reef areas, including at least 800 species of stony corals. Except for rain forests, coral reefs contain more living species than any other type of ecosystem. Indeed, coral reefs often are called the "rain forests of the oceans."

Reefs