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4 Kinds of Coral Reef
Coral reefs are underwater rock outcrops covered by a thin layer of living coral polyps. These outcrops can be huge, sometimes over a kilometer (1 km = 0.7 miles) thick and hundreds of kilometers in length. But the coral polyps that build these massive structures form a layer only a few millimeters thick (1 mm = approximately 1/32").
Reef-building coral polyps live in a protective shell made from calcium carbonate (CaCO3), and as they divide and grow they form colonies. These colonies form the basic structure of the reef, helped by other organisms, like coralline algae. Building a reef is a slow process because the coral that form reefs grow about 0.3 - 2 cm (5/16 -13/16") each year. It is estimated that coral polyps need about 10 000 years to form a reef, and 100 000 to 30 million years to build a fully mature reef.
Polyps are only able to build a reef with the help of single-celled zooxanthellae algae. Polyps provide zooxanthellae with nutrients and shelter, and receive food in return. Zooxanthellae algae require sunlight for photosynthesis, and coral reefs usually begin to form in clear, shallow waters near land because water gradually filters out sunlight with depth.
This relationship with land is used to categorize the different types of coral reef. 4 main types of reef exist:
Fringing reefs, barrier reefs and atolls are thought to represent stages in coral reef formation. Charles Darwin first proposed this theory of coral reef formation in 1842.
Step 1: A fringing reef forms first, and starts growing in the shallow waters close to a tropical island.
Reefs require very similar conditions to develop and are subject to similar forces from the open ocean. This means that similar types of reefs form under the same conditions even if they are on opposite sides of the world.
Achituv, Y. & Dubinsky, Z. (1990). Evolution and Zoogeography of Coral Reefs. In Ecosystems of the World: 25 Coral Reefs. Dubinsky, Z. (ed.). Elsevier, New York.
Anderson, G. (2003). Coral reef formation. MarineBio.net. Retrieved 5 September 2008 from http://www.marinebio.net/marinescience/04benthon/crform.htm
Birkeland, C. (1997). Introduction. In Life and Death of Coral Reefs. Birkeland, C. (ed.). Chapman and Hall, New York.
Darwin, C. (1842). The structure and distribution of coral reefs. [Reprint by University of California Press, Berkeley 1962]
Hatcher, B.G. (1997). Organic Production and Decomposition. In Life and Death of Coral Reefs. Birkeland, C. (ed.). Chapman and Hall, New York.
NOAA. (2008, March 25). How do coral Reefs form? NOAA National Ocean Service Education. Retrieved March 25 2008 from http://oceanservice.noaa.gov/education/kits/corals/coral04_reefs.html
Wikipedia. (2008, March 25). Coral Reef. Wikipedia. Retrieved March 25, 2008, from http://en.wikipedia.org/wiki/Coral_reefs
Wright, D. & Duncan, B. (2007, June 4). OC/GEO 103 Lecture - Ocean Habitats - Coral Reefs. Department of Geosciences, Oregon State University. Retrieved March 26, 2008, from http://dusk2.geo.orst.edu/oceans/lec25_ocean_hab.html
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