Starfish Copyrighted image Credit: BBC

A sandy beach is the ideal spot for relaxing in the sun, sipping a cold drink and reading a book.

There are seagulls about, but otherwise it looks like a beautiful but lifeless habitat. Yet look for clues on the surface at low tide and you may find some interesting fellows hiding in wet sand, where they are protected from drying out.

On some beaches you find large worm casts, each about six to ten centimetres from a small circular depression in the sand. The worm cast marks the rear end of a lugworm in its U-shaped burrow, and the depression marks where the head is eating sand.

Collect some sand from this area, digging to about 30 cm depth; now collect another sand sample from an area without lugworms. Put each sand sample into a tall plastic water bottle and add seawater; shake each bottle, then allow the sand to settle.

You should see layers of sediments arranged according to particle size; the largest sand particles are on the bottom, and light organic matter is at the top. Compare the layers in your 2 bottles. Which bottle contains the most organic matter? Suggest why lugworms are common in one part of the beach, but not in another.

Lugworms on a beach Copyrighted image Credit: Flickr CreativeCommons evilnick http://www.flickr.com/photos/32655742@N00/83796942/ Lugworms on a beach [Image: evilnick - CC-BY-NC-ND licence]

Molluscs such as cockles, tellin and razor shells hide in wet sand; dig in the sand to look for them, or collect their empty shells.

Higher up the beach on the strand line, there is dead seaweed, driftwood and litter. Disturb the seaweed and sand and you may see jumping sandhoppers - small shrimp-like crustaceans that eat rotting seaweed.

Animals in the sand are part of the food web of a sandy shore. Birds, turnstones, rock pipits and sandpipers hunt for sandhoppers on the strand line.

Look for clues that indicate which predators ate the inhabitants of your seashells.

Small round holes in tellin shells were bored by necklace shells - predatory snails that scrape out and eat tellin alive. Cockleshells with large jagged-edged holes were smashed by the stout beaks of oystercatchers. So a sandy beach is not always a lifeless habitat; on the contrary there may be a varied community of animals there, providing food for fish, sea birds, and humans.

Lugworms digest rotting organic matter from dead animals and seaweed, which is mixed with sand and mud. They cannot feed in ‘clean’ sand.

This article was originally published Summer 2005 as part of the Coast postcards pack