User:Phoebe/coral
From Wikipedia, the free encyclopedia
coral reef article revision -- 12/12
A coral reef is a type of biotic reef that develops in tropical waters by reef-building, or hermatypic, corals.
Coral reefs are found in all oceans of the world, except the Arctic Ocean, generally between the Tropic of Cancer and the Tropic of Capricorn. Water temperature of 20–28 °C (68–82 °F) is an optimal range for proper growth and health of coral reefs. Reef-building corals cannot tolerate colder waters, although there are cold-water corals that do not produce reefs.
Reef-building corals are also only found in the photic zone (<50m), the depth to which sufficient sunlight penetrates the water for photosynthesis to occur. The corals themselves do not photosynthesize, but instead live in symbiosis with zooxanthellae, single-celled algae that photosynthesize and produce excess nutrients that are used by the corals. Because of this, coral reefs also grow much faster in clear water, which absorbs less light.
Reefs may also be built or contributed to by calcareous algae, especially (although not entirely) species of red algae.