The Facts

• Corals belong to the group cnidaria, which includes other tiny animals such as jelly fish and anemones. Individual corals, or polyps, live in large stationary colonies and feed on passing animal and plant life. Corals excrete calcium carbonate that hardens and forms a rock like skeleton that becomes the physical reef. According to the U.S. Environmental Protection Agency, "the calcium carbonate is secreted at the base of the polyps, so the living coral colony occurs at the surface of the skeletal structure, completely covering it. Calcium carbonate is continuously deposited by the living colony, adding to the size of the structure." The living colony of coral on a reef makes up only a thin layer compared with the large structure of the reef.
  
  

Significance

• Besides being tourist destinations, coral reefs serve many functions in the world's oceans. The National Oceanic and Atmospheric Administration identifies coral reefs' importance to the future:
  1. They serve as the home and nursery to many fish and other animals that humans rely on for food.
  2. Coral reefs are some of the most diverse living ecosystems on Earth.
  3. Coral reefs are a potential biomedical resource.
  4. Coral reefs offer physical protection from storms and erosion to coastal communities.
  
  

Three Types of Coral Reefs

• Fringing reefs extend from shore into the ocean.
  
  Barrier reefs are separated from the land by a body of water. For example, the Great Barrier Reef lies off the coast of northeastern Australia and is the world's largest coral system. It stretches more than 1,600 miles and can be seen from outer space.
  
  Atolls are reefs that form on the tops of submerged volcanoes. These reefs can eventually form islands, such as the many atolls in the South Pacific.
  
  

Considerations

• The hardened calcium carbonate structure of a coral reef can survive for millions of years, but according to the National Oceanic and Atmospheric Administration, the thin living layer of coral is fragile and can be damaged by human and natural interference.
  
  

Expert Insight

• According to the EPA, "The calcium carbonate is secreted at the base of the polyps, so the living coral colony occurs at the surface of the skeletal structure, completely covering it. Calcium carbonate is continuously deposited by the living colony, adding to the size of the structure." The living colony of coral on a coral reef makes up only a thin layer compared to the large structure of the reef.