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Coral reefs are home to an estimated 2 million species, corresponding to about 25% of the world’s marine life. Even though coral reefs occupy less than 1% of the ocean surface, they make up one of the largest, most biologically diverse, and economically important ecosystems on the planet.

Coral reefs are the source of 25% of the world’s seafood, are an important source of tourist income for local communities, provide a potential source for new medicines and bio-materials, and provide a valuable barrier against coastal erosion.

Coral Building Blocks*

Corals are similar to sea anemones but differ in having a limestone skeleton inside their tissues. The coral animal, or polyp, has a simple gut that opens at one end at a mouth surrounded by tentacles – also called the oral disc. The polyp lives in a cup-like skeleton called a corallite. The polyp secretes this limestone (CaCO3) skeleton from its tissue. The entire coral colony (tissue and skeleton) is known as a corallum or coralla (plural).

Coral Lifestyles*

Corals with more than one corallite form a colony. Corals that live their entire life as a single polyp are solitary corals. Solitary corals can range in size from 0.5 – 50 cm.

Most coral colonies begin life when a coral larva settles from the plankton to form a single polyp / corallite. A colony is formed by cloning copies of the original polyp. Some isolated corals are solitary, others are large single polyp juveniles that will grown into colonies. Most corals are attached (cemented) to the seafloor but some spend their life unattached and are free-living.

For more information on coral biology and for access to the Coral Finder that assists in identifying corals underwater, visit the Coral Hub (

* Text from the Coral Finder with the kind permission of Russell Kelley. The Coral Finder is published by Russell Kelley, P.O. Box 1859, Townsville, QLD 4810, Australia (

• El Niño Southern Oscillation
• Global Impact of Carbon Dioxide
• Ocean Acidification

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