Coral Reefs

How coral reefs are built

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A diversity of corals on Flynn Reef near Cairns (Wikipedia: Coral Sea, via

How Coral Reefs Are Built 

A variety of marine creatures ultimately contribute to the complex structure of coral reefs. However, most of the underlying solid framework of coral reefs is constructed by the slow, cumulative efforts of just one particular group of simple, tiny animals called the hard (Scleractinian) corals.

In these corals, the body of each individual animal (called a polyp) is encased in a hard external skeleton composed of calcium carbonate and formed by the animal itself from substances extracted from seawater. Another quite different type of coral (commonly called fire coral) sometimes also substantially contribute to the framework of shallow Caribbean reefs.

As adults, hard corals typically exist as parts of large cohesive assemblages called colonies, in which only the outermost layer is composed of living polyps. Each coral colony is composed of many genetically identical individual polyps, with succeeding generations built upon the skeletal remains of ancestors. Colonies of hard coral typically grow in larger assemblages composed of many interconnected colonies of the same or different species.

Other major contributors to the reef-building process include an unusual group of plants called coralline or calcareous algae which, like the hard corals, also incorporate calcium carbonate into their bodies. The coralline algae grow amidst and around the individual coral colonies forming the reef, helping to build and cement the entire reef structure into a strong and cohesive formation.

Upon the underlying foundation built by hard corals and calcareous algae grows a diverse assortment of other creatures - a superficial layer of sponges, octocorals, other invertebrate animals, and certain types of marine algae that anchor to the reef surface and together provide an added dimension of structural and biological complexity and diversity to coral reefs.

Further Reading:

Coral Reef Facts and Information:

Disclaimer: This article is taken wholly from, or contains information that was originally published by William Alevizon, Ph.D. in Ezine Articles. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the (organization name) should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.



Alevizon, W. (2014). How coral reefs are built. Retrieved from


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