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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 coastline that is underwater at high tide and above the water at low tide. Whether it’s a rocky coast, a sandy beach, or a salt marsh, life in the intertidal zone needs to be able to survive extreme conditions - both above the water and below.  When the tide is low and the intertidal zone is above the water, the things that live there can be exposed to warmer temperatures and brighter light than they were below the water. At high tide when the intertidal zone is covered with water, the living things can be pounded by waves.

Conditions are more like living on land for creatures in the upper part of the intertidal, which is only covered with water at extreme high tide.  Conditions are more like living in the ocean for creatures in the lower part of the intertidal which is only exposed to air at extreme low tide.  Because of this, different animals, plants, and algae can survive in different parts of the intertidal zone.  Some are better adapted to living in the upper intertidal, while others are better adapted to living in the lower intertidal.

On rocky coastlines, there are often many types of algae and small snails that eat the algae. Animals that attach to the rocks such as barnacles, a type of crustacean, and mussels, a type of mollusc, are often found on rocky coasts.  Sea urchins and sponges can live in areas that are usually covered with water.

There are often tide pools in rocky coastal areas – small pools of water in the intertidal zone that remain even after the tide goes out. The animals, plants, and algae that are found in tide pools are often the same species that are found in the nearby shallow ocean waters.

Coastal marshes, or wetlands, form in areas that are protected from waves. They usually have soft mud, quiet water, and grasses. Molluscs like clams and mussels live within the mud. Some molluscs, such as oysters, live on top of the mud. Many types of microscopic plants live in the mud too. Crabs, fish, and shrimp are also common in marsh areas.

On sandy coastlines, the intertidal zone is often home to animals that live in burrows within the sand such as clams and worms. Crabs scurry across the sand but often have burrows that they retreat to as well. This environment is often where large waves crash, so living in a burrow offers some protection.

Last modified June 1, 2010 by Lisa Gardiner.

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