Searching for seashells at low tide in the intertidal zone along the rocky and sandy coast of Brittany, France Click on image for full size (89 Kb) Courtesy of Annette Pharamond

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.

Searching for seashells at low tide in the intertidal zone along the rocky and sandy coast of Brittany, France Click on image for full size (89 Kb) Courtesy of Annette Pharamond

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.

Searching for seashells at low tide in the intertidal zone along the rocky and sandy coast of Brittany, France Click on image for full size (89 Kb) Courtesy of Annette Pharamond

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.