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Paleo Slide Set: Coral Paleoclimatology
Branching coral Pocillopora damicornis from the Gulf of Panama (8N, 79W).
We see that corals are in fact colonies composed of hundreds of thousands of tiny animals called coral polyp. The polyps in this photo of the branching coral Pocillopora damicornis look like tiny bushes. To simplify things, think of a polyp as a hollow fleshy column sitting in a hard cup. On the side of the column that comes into contact with water, a ring of tentacles capture tiny organisms called plankton and direct them down the column and into the pharynx to be digested. Most reef-building corals also have an alternate source of food: a type of algae called zooxanthellae live within the fleshy parts of coral polyps. These algae give living corals their brownish color. Zooxanthellae photosynthesize light and carbon dioxide to supply both themselves and the coral with food and oxygen. In turn, the food caught by the coral supplies both organisms with the crucial nutrients phosphorous and nitrogen, which are then cycled back and forth between the two. Algae also help corals with calcium carbonate deposition and without algal populations corals are unable to produce substantial reef structures. This interdependent relationship between corals and the algae they contain is an example of symbiosis, a biological term describing a relationship where two organisms work together to survive.

Photo Credits:
Jerry Wellington
Department of Biology, University of Houston
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Last Modified: 12 October 2001

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