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Corals are tiny animals that live in colonies and derive nourishment and energy from a symbiotic relationship with algae known as dinoflagellates.

Corals are actually clear. Corals get their bright, diverse colors from the algae that lives inside their tissues. The relationship between the coral and the algae is symbiotic. The coral gets nutrients and energy from the algae and the algae get a safe place to live within the corals.

Corals are the oldest living animals on Earth. Coral reefs are formed over the course of thousands of years as limestone skeletons constructed by corals accumulate and form a structural base for living corals. Research indicates that it takes roughly a thousand years for a reef to add a meter of height. Individual corals are capable of faster growth -- about one meter every hundred years -- but wave action and other forms of disturbances moderate overall reef growth.


Why should I be aware of this?

  • Corals support an estimated 25% of all marine fish species.
  • Coral reefs provide food, protection, and income for more than 100 cultures around the world.
  • Coral reefs in 93 countries have been damaged or killed by human activity.
  • Corals are an important past of the marine ecosystem.

How does this affect me?

  • The degradation and loss of coral ecosystems is likely to have a wide-ranging impact on the world economy.
  • More than 500 million people live within 100 kilometers of coral reefs, many of whom rely on reefs and the services they provide for daily subsistence.
  • Coral reefs play an important role in buffering adjacent shorelines from wave action, erosion, and the impact of storms. For example Moorea in French Polynesian, only experiences a 10 cm tidal range due to its protective barrier reef. Should the reef die and begin to crumble, the island's low-lying structures could be at risk.

All about corals

Fragile as sugar lace on top, coral is bound like cement to the ocean floor. Only the top layer is alive. The lower part comprises compacted skeletons of old coral polyps glued together to form a solid calcium carbonate basement. Drill samples from reefs in the Indian and Pacific oceans suggest some are hundreds of meters thick.

  • Coral consists of many colonial animals.
  • Each animal's body is a soft, fleshy bag with a mouth and sticky tentacles (some with stinging cells).
  • The mouth also serves as the anus.
  • The individual is protected by a self-secreted calcium carbonate house.
  • The body tissue is connected to others in a colony so that nutrients can be shared.
  • The different shapes of coral help define their species, while their wild variety of colors are shared by many types.
  • The assortment of reds, purples, greens, and browns are usually created by live-in plants.
  • The basic coral skeleton is white.

Types of corals

Corals can be devided into two types with respect to the way they feed.

  1. The shallow water corals frequently seen by snorkelers receive nearly all their nutrition through their algae. These alga use carbon dioxide and sunlight to produce carbon compounds and oxygen for the coral polyp.
  2. The deeper water corals with less exposure to sunlight. They use stinging cells to capture their food. They mostly live on tiny zooplankton, but some are actually able to capture and eat small fish.

Threat to corals

  • Bottom trawling
  • Bleaching

Coral bleaching

When water temperature rises, coral become stressed. This leads to bleaching where they lose much of the their symbiotic algae. Corals can recover from short-term bleaching, but prolonged bleaching can cause irreversible damage and subsequent death.

  • The first coral bleaching on record occurred in 1979.
  • In 1998, coral reefs around the world suffered the most severe bleaching on record. 48% of reefs in the Western Indian Ocean suffered bleaching, while 16% of the world's appeared to have died by the end of 1998.
  • In 2002, 60 to 95% of individual reefs of the Great Barrier Reef suffered some bleaching, while reefs in Palau, the Seychelles, and Okinawa suffered 70-95% bleaching.
  • Early surveys suggest the Caribbean is currently in the midst of a serious event. While most of these reef ecosystems have recovered to some degree, warmer water.

See also


  • Coral
  • Introduction: What is a coral?
  • Awareness & Outreach
  • Conservation Corals]