Summer 2002

Life's a beach

Article by Paul Wisse, Technical Services, Sefton Council

There's life in the old girl yet! Sefton's beaches have been around for several thousand years and are still going strong. Traditionally the beach has been used for playing, walking, watching birds and, weather permitting, sunbathing. However, there is a little more to the shore than meets the eye. The expansive sandy beaches and mud flats on the coast often appear lifeless, but on closer inspection there is a large abundance and variety of life hidden just below the surface.

The majority of animals living in the shore are marine invertebrates, animals without a backbone, such as molluscs, crustaceans, echinoderms and worms. They generally hide away when the tide is out and only become active when the tide is in.

There are many challenges facing the animals that try to survive on the shore. To avoid drying out when the tide is out they bury themselves in the sediment where it is cool and damp.

These animals are subjected to a constant barrage of bills, pincers and mouths all trying to get a tasty snack. When the tide is out a large number of wading birds are attracted to the shore to plunder this food source. If the birds aren't feeding then often bait diggers are collecting worms to go fishing with. With the coming of the tide these hunters are forced off the shore and the inhabitants can go about feeding themselves. They feed on organic matter present in the sediment and brought in by the tide, and each other! However, along with the tide comes another set of hungry mouths, those of several species of fish and crustacean, also intent on exploiting this rich food source.

If the invertebrates are lucky enough to survive the onslaught of feeding animals they are still at the will of the nature. Strong waves and tides easily disrupt the sediment and the inhabitants can be washed out of the sediment and deposited openly onto the shore. This is particularly common after storm events. Often this is the only evidence of the animals living in the shore.

A stroll along the shore can reveal evidence of these animals. At low tide the lower shore may show evidence of Lugworms and Sand Mason worms. The Lugworm digs a 'U' shaped burrow, with an inlet and an outlet. The worm filters sand and extracts nutrients from it; this filtered sand is then deposited on the shore as a cast. The Sand Mason worm constructs a rigid tube by sticking together sand and shell particles, when the tide is in they collect food particles from the seawater using tentacles. These tubes can be found washed up on the shore and it is possible to find inhabited tubes on the extreme low shore.

A huge variety of shells can be found on the shore. Of these the most conspicuous are those of the razor shells. These long molluscs bury vertically into the sand and filter seawater for food. Other common shells include the cockle and tellin shells; these two species are a particular favorite of many wading birds. If you are luck you may find the old shells of the masked crab and shore crab. These two species actively predate on the other animals found in the shore especially the soft-bodied worms.

The test of the Sea potato can be found on the beach. The sea potato is an echinoderm, the same group as the starfish. They normally live around the mean low water mark buried in a permanent burrow in the sand up to 15cm deep. They feed off detritus in their burrow and around the opening of the respiratory channel using their tube feet.

If you plan to explore the beach please take care and check tide time before venturing onto the shore. If in doubt ask a lifeguard or site staff. Always keep an eye on the tide as it rises very quickly. It is best to avoid the muddy areas as they can be dangerous.