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  • Japan (Head Office)
  • North America
  • Latin America &
    the Caribbean
  • Europe
  • Africa
  • Middle East
  • Central Asia
  • East Asia
  • Asia & Oceania

Japan (Head Office)

North America

Latin America & the Caribbean

Please see details of our activities in Latin America & the Caribbean here.

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Central Asia

Mitsubishi Corporation

What is a coral reef?

Creating extremely beautiful seascapes, a coral reef gives grace to living things. To consider why it is so important to conserve coral reefs, let's look at what kind of creatures are coral.

What is a coral?

What is a coral?

There are probably some people who take one look, and not seeing any movement, think that these reef-building corals are either "plant" or "mineral." Corals are in fact members of an animal phylum called Cnidaria, whose other members include sea anemones and jellyfish. A coral is actually formed by many tiny individual bodies clustering into groups. As shown in the illustration on the right, a single coral is made up of bodies called polyps and a calcareous skeleton. Corals grow in different shapes: branch shapes, table shapes and rock shapes. Layers and layers of them build up to form the complex topography of the reef. Polyps have a mouth surrounded by tentacles. Through these mouths, polyps feed, excrete waste, and spawn. Inside the polyp's cells live algae forming a symbiotic relationship with the polyps.

Corals are the entirety of a cluster of many polyps.

As shown by the illustration, a coral is a member of the Cnidaria phylum; it feeds, spawns and has both a mouth and a stomach. Within the body of corals are many botanical plankton called zooxanthellae.

What is a coral reef?

A coral reef is the name given to a "geological formation," rising nearly to the level of the sea surface, built over a long time layer by layer by the calcareous skeletons created by corals. The ecological activity of corals is influenced by a variety of factors including the other creatures that coexist in the area and the nutrient content of the water. Many of the coral reefs that can be seen in the world today have been around for over 5,000 years. There are reef throughout the world in more than 100 countries and the total area of coral reefs is said to exceed 600,000 square kilometers.

Broadly speaking, there are three different types of formations that coral reefs take.

Fringing reef

Fringing reef

A fringing reef is a formation whereby a reef is directly attached to a shore. When land is created by undersea volcanic eruptions or tectonic movement in marine environments appropriate for coral growth, coral establishes itself in the shallows surrounding this land. The coral extends outwards as it continues to grow and fringes around islands like a lace hem.

Barrier reef

Barrier reef

A barrier reef is a formation whereby a reef is separated from a shore by a shallow sea (lagoon) tens of meters deep. Fringing reefs exposed to the outer seas develop into barrier reefs when over a long period of time the island or mainland sinks lower than the sea level because of movement in the earth's crust or a rise in sea levels.

Atoll

Atoll

An atoll is a formation whereby an island completely submerges beneath the sea level so that all that remains is the coral reef forming a string of islands in the shape of a ring. Small islands can form as the result of sand accumulating above the reef. Many atolls exist in the Maldives and the Marshal Islands.

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