Classification of Reef Building Corals

Here you will learn about vital functions of corals, their taxonomy and classification.

Taxonomy: Living creatures are called organisms. Taxonomy is the method of naming organisms for universal reference. This is necessary because in different areas of the world, the same animal can be called different names. For example, a bobcat, mountain lion, and puma are all the same animal. It would get confusing if scientists used all these different names, so taxonomies are used to keep names the same across the entire world. Aristotle was the first to classify organisms and described among others some cnidarians. The taxonomy system of plants and animals now used throughout the world is based directly off the Carl Linnaeus work, Swedish botanist living in 18.th century. Contemporary scientists use this method of classification because it simply works. You might also hear taxonomy called nomenclature, or naming. Taxonomy and nomenclature both refer to the same idea.

Classification: Organisms are classified into different categories based upon similar characteristics. As you would expect, a human and a monkey are closely related because they are similar in appearance. A monkey and a snail are less similar to each other than in the previous example.

See: the shortened taxonomy
Some of types listed in those taxonomy are described in Gallery section.

Corals that belong to the Scleractinia are divided into two main groups.

Corals that produce coral reefs live in warm and shallow water, and need sunlight for their symbiont zooxantellae (only shallow water coral constructions are called reefs). The corals that live in deep and cold water and are lacking such symbionts usually live as isolated solitary or colonial forms and only exceptionally build big constructions (not called reefs).

This site will almost exclusively be dealing with Hermatypic Corals only.

Shallow-water scleractinians are the main builders of reefs. These are tiny animals living in colonies. Most of them are only 2 to 3 millimeters (mm) in diameter. However, size can vary among corals. The living coral only exists in the top layer of the coral reef. Moment by moment, that thin layer of living coral works to construct massive structures that radiate amazing colors!

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Hermatypic scleractinians grow only in special conditions:

1) Depth – Reef building corals live in between the water’s surface and a maximum depth of about 90 meters. Few corals will be found past 50 meters below the surface, however. Corals that do not live in symbiosis with algae do not need sunlight to produce their skeleton. These are ahermatypic species that live in the deep sea. A few species may even live at depths of 6,000 meters below the surface.
2) Temperature – Hermatypic corals live in warm water: from 18° C to 36° C. The ideal temperature for corals to live in is between 25° C and 29° C. Ahermatypic corals can live in temperatures as low temperature as 4° C. A few species can even survive in temperatures of 1° C.
3) Salinity – Hermatypic corals tolerate salinity between 27 and 40 parts-per-thousand. Corals thrive best in water with a salinity level of 36 parts-per-thousand.
4) Light – All corals living in symbiosis with zooxanthellae need strong source of sunlight. There are, of course, the few exceptions of corals that live in the deep sea. These coral exceptions may live in symbiosis with algae while being receiving almost no sunlight.

In general, hermatypic corals live in the shallow water that borders both islands and continental shelves in a warm climates. These warm climates are located within the latitude of 32° 30’N to 30° S.

Coral Reefs