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Searching for seashells at low tide in the intertidal zone along the rocky and sandy coast of Brittany, France
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Courtesy of Annette Pharamond

Life in the Intertidal Zone

The intertidal zone is the area along a coast that is underwater at high tide and above the water at low tide.

Creatures that live in the upper part of the intertidal zone are only covered with water during very high tides.  Creatures in the lower part of the intertidal are only exposed to air during very low tides.  Some plants, animals, and algae prefer to live in the upper intertidal, while others prefer the lower intertidal.

On rocky coasts, you can usually find slippery algae on the rocks. Other rocks might have a rough surface because they are covered with animals that have hard shells like barnacles and mussels.  You might find sea urchins and sponges in places that are usually covered with water. There are sometimes small pools of water between rocks that remain even after the tide goes out. These are called tide pools and they are often filled with many different animals, plants, and algae.

Marshes can be found in areas that are protected from waves. They usually have soft mud, quiet water, and thick grasses. At low tide, the mud is exposed to the air. You can often find molluscs like clams, mussels, and oysters in and on the mud. You might also see crabs, fish, and shrimp. Tiny plants that are too small to see are in the mud too.

On sandy beaches, animals like clams live in burrows within the sand. If they are in their burrows, you might not see them. But you can often find seashells on the beach from clams that have died. Living in a burrow protects the animals from large waves that often crash along sandy beaches.

Last modified June 1, 2010 by Lisa Gardiner.

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The Spring 2010 issue of The Earth Scientist, focuses on the ocean, including articles on polar research, coral reefs, ocean acidification, and climate. Includes a gorgeous full color poster!

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