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A Coral animal
is actually a colony of small bag
shaped organisms called polyps.
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An individual
polyp may be the tip of your little finger.
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The mouth of the
bag is surrounded by tentacles that are used for feeding.
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The base of the
polyp is important because this is the area that secretes the
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small,
protective calcium carbonate cup into which the polyp can partially
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withdraw when threatened.
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The polyps are
connected to each other laterally forming a thin layer of tissue
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over the calcium
carbonate skeleton, which may eventually grow from the
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size of a marble
to size of an automobile.
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The cells of the
polyps contain single celled plants called zooxanthelae,
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between 500,000
and 5,000,000 per square centimeter. The symbiotic
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relationship
between the host coral and the resident primary producers,
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zooxanthelae,
provides the corals with nutrients in quantities that
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would otherwise
be unviable in the nutrient poor tropical waters
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of the
Caribbean. This allows corals to grow more rapidly than they would be able
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to if they had
to absorb their nutrients from the surrounding waters,
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or from digested
prey. The zooxanthelae also give corals their colour.
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The two
important characteristics of corals to remember are that
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they secrete
massive calcium carbonate skeletons,
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and that they
contain symbiotic single celled
algae.
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