Ocean life
Seashore
The seashore is the place where the land meets the sea. It can consist of rocky cliffs, a sandy beach or mudflats bordering a river mouth or estuary. The animals and plants that live there must be able to survive the tides that cover them in salt water at certain times of the day, and leave them exposed to the air at other times. They live at different levels on the seashore according to how well they can survive out of water.
Seaweed
Many kinds of seaweed dry out easily, and are found low down on the shore where they are covered with water all the time. Other more hardy varieties live farther up the shore. They do not put down roots into the ground, but anchor themselves to rocks to stop themselves being pulled away at high tide. They are covered with mucus to hold in moisture when the tide goes out. This provides small animals with shelter from the Sun.
Seaweeds belong to one of several groups of algae: brown algae (including kelp and the wracks, such as bladderwrack), red algae (including Irish moss) and green algae (including sea lettuce). They have stem-like parts and leaf-like blades, called fronds, but they are not true plants. In many parts of the world, seaweed is harvested and used as a food or a food additive.
Surviving low tides
Animals that live on sandy or muddy shores burrow into the ground at low tide, to keep moist and cool. On rocky shores, mussels clamp their shells tightly together, while limpets attach themselves to wet rocks to stop themselves drying out. This also prevents them from being pulled away by powerful waves when the tide comes back in. On some shores, tidal pools form between rocks. These are rich in life, including animals such as starfish, sea anemones and small fish, which could not otherwise survive so far up the shore. Wading birds, such as curlews or oystercatchers, use their long beaks to probe through the sand on a beach in search of worms and shellfish.
Rock pools
On some seashores, pools of water are left between the rocks when the tide goes out. Crabs, starfish, prawns and small fish live in these rock pools. Algae growing on the rocks are eaten by limpets, sea snails and periwinkles, which are themselves prey for starfish and whelks. Seaweeds are also a source of food, as well as a cool, damp shelter for them when the tide goes out. Crabs such as the hermit crab, which takes over the shell of a dead animal, scavenge on animal debris. Wading birds probe the pools and shore for worms, fish and shelled animals.
High tide
At high tide, much of a low-lying seashore is under water. The sea carries sand, pebbles and other material which it leaves on the shore. It also brings tiny particles of food for the many small creatures that live in the sand or on the rocks. These creatures are, in turn, prey for crabs, starfish and sea birds.
Consultant: Chris Jarvis