Coral: Difference between revisions

Revision as of 19:52, 11 December 2003

Revision as of 14:37, 13 December 2003

Line 2:

<div style="float:right;margin-left:0.5em; margin-bottom: 0.5em">[[Image:Reef0484.jpg]]</div>

'''Corals''' are marine [[cnidaria]]ns (Phylum: '''Cnidaria'''; Class: '''Anthozoa''') existing as small anemone-like polyps, typically forming colonies of many individuals. The group includes the important [[reef]] builders known as hermatypic corals, found in tropical [[ocean]]s, and belonging to the Subclass: '''Zoantharia''', Order: '''Scleractinia''' (formerly Madreporaria). The latter are also known as ''stony corals'' in as muchinasmuch as the living tissue thinly covers a skeleton composed of [[calcium carbonate]]. The hermatypic corals obtain much of their nutrient requirement from [[symbiosis|symbiotic]] unicellular [[alga]]e called [[zooxanthella]]e, and so are dependent upon growing in sunlight. As a result, these corals are usually found not far beneath the surface, although in clear waters corals can grow at depths of 60 m (200 ft). Corals breed by spawning, with all corals of the same species in a region spawningreleasing their [[gamete]]s simultaneously on a few nights around full [[moon]].

There are several other types of corals, notably the octocorals (Subclass: '''Octocorallia''') and corals classified in other orders of Subclass: '''Zoantharia''': to wit, the black corals (Order: '''Antipatharia''') and the soft corals ('''Order Zoanthinaria'''). Most other anthozoans would be treated under the common name of [[Sea anemone|''anemone'']].

Line 17:

</div>

Coral can be sensitive to environmental changes, and as a result are generally protected through environmental laws. A coral reef can easily be swamped in [[algae]] if there is too much [[nitrogen]] in the water. Coral will also die if the water temperature changes by more than a degree or two and becomes too hot or too cold or if the salinity of the water drops. In an early symptom of environmental stress, corals expell their zooxanthellae; without their symbiotic unicellular algae, coral tissues are colorless, revealing the white of their [[calciumn carbonate]] skeletons, an event known as '[[coral bleaching]]'. A combination of temperature changes, pollution, and overuse has led to the destruction of many coral reefs around the world. This has increased the importance of [[Coral Biology]] as a subject of study.

Ancient coral reefs on land are often mined for limestone.