Class: Anthozoa
Corals come in all shapes and sizes--some are reef-builders while others are non reef-builders:
Corals come in all shapes and sizes--some are reef-builders while others are non reef-builders:
The reef builders are the corals that can be seen in the Great Barrier Reef off Austrailia. Reef builders build high structures composed of living and non-living materials. The living materials are most often sponges, algae, and the corals themselves. The non-living materials are most often the discarded shells of dead bivalves (clams, mussels, etc.) and other CaCO3 materials. Coral reefs grow about a meter every one thousand years, so you see why it's very difficult for a reef to recover if it is destroyed.
Non reef-builders usually inhabit the bottom of more shallow areas of the ocean. They do not build high structures.
An example of a Fire Coral, a non reef-builder.
Corals are invertebrates that are in symbiosis with an algae (phylums: chlorophyta, rhodophyta, or phaeophyta) or a dinoflagellate (phylum: dinophyta)--that means they exchange nutrients or other services with one another in order for both to survive better. They are of the phylum cnidaria and therefore have an alternation of generations during their life cycle (this cycle alternates from a polyp to medusa stage). However, the class anthozoa's medusa stage is absent and once they fix themselves in one place, they become sessile. They only move during their developing stages. To obtain food, corals filter feed.
Coral bleaching occurs when the corals lose their algae (the algae or dinoflagellate is what cause the beautiful colors that a coral has). The result of losing its algae causes the coral to "bleach" (become completely white). Scientists are not quite sure why this happens, but there is some evidence to suggest that a rise in water temperature may be involved. Most organisms' metabolisms cannot handle even a small change in temperature. A possible cause of this rise in temperature is the heavily debated global warming situation.
