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. Life in the intertidal zone needs to be able to survive extreme conditions - both above the water and below.  When the tide is low, living things are out of the water and they can be exposed to heat and bright sunlight. When the tide is high 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.  Some plants, animals, and algae 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 and mussels can be common.  Sea urchins and sponges live in areas 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.

Coastal marshes, or wetlands, form in areas that are protected from waves. They usually have soft mud, quiet water, and grasses. During low tide, the mud is often exposed above the water. Molluscs like clams, mussels, and oysters can be found in and on the mud. Crabs, fish, and shrimp are also common in marsh areas. Many types of microscopic plants live in the mud too.

On sandy beaches, 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 and usually have burrows too. Large waves often crash along sandy beaches, so living in a burrow offers some protection.

Last modified June 1, 2010 by Lisa Gardiner.

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