World Builders™
World Builders™
Session Six  --  Water Animals
Session Six  --  Water Animals s



Cnidaria -- Corals
Cnidaria -- Corals

Corals are members of the same phylum as jellyfish and sea anemonies.

     Corals and sea anenomes look like plants to us, but they are animals: they cannot make their own food. These corals live in a beautiful reef where the sea currrents bring them a constant stream of food. Corals are communities of little animals that live together. They have moving tentacles and they catch whatever floats by in the ocean currents. They are able to pull in their tentacles when something touches them.

Why are there corals here, but not plants? Plants can get more light closer to the surface. Perhaps the corals, nourished by organic particles in the water, can grow fast enough to crowd most plants out.

Corals grow in very clear, warm water.  Green algae grow inside the cells of the coral, and give off oxygen and some organic material ,which nourish the corals.  The algae are protected from grazers and strong water currents, so both parties benefit. 

This is an example of two different ecological niches, places in a larger system where species thrive by specializing on living on a portion of the resources. In this way they are not competing with each other for the same resources. Everybody gets his own slice of the pie!

When the water is heated by sunlight more than usual, the corals expel the little algae in their cells.  Then the corals starve and die.  Living creatures are dependent on the stability of their environments.  They adapt to the conditions, but are not adapted to sudden changes.  Right now many coral reefs are dying.  The scientists believe that this is partly because global warming is making the ocean warmer.  Coral reefs are very rich environments, and many different kinds of fishes and other animals live in the shelter that they provide.


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Photos from archives at Biology Department, University of Bowling Green, Ohio
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© 1996,1997, 1998, 1999, 2000, 2002, 2003.   Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at eviau@earthlink.net .