Coast & Sea Areas

Wild Harris

Sand and Mud Shore Animals

Shores made up of loose material are difficult to colonise by animals or plants that need a firm foundation, but they do allow animals to burrow down into the sediment. This offers protection from the weather and predators when the tide is out. The size of the particles that make up soft shores depends on the strength of the wave action - in general the more violent the water movement, the larger the particle size. Very coarse sediments, such as shingle, are almost devoid of life because of the crushing effect of the pebbles as they are rolled around by the surf. Coarse sand supports some burrowing animals, but its the soft stuff such as fine sand and mud that supports the greatest densities of animal life. This is not just because the wave action is gentle; food in the form of organic debris is usually lightweight material which will not settle out unless the wave action is gentle, so whereas a shore made of coarse sand will contain little organic matter, a muddy shore may contain a huge amount. It is this material that provides food for the thousands of burrowing animals that live in such sheltered areas. These in turn provide a bountiful food source for wading birds, which is why you find so many birds with long probing bills such as oystercatchers and curlews on these shores.

scarista waves.jpgScarista Waves    (Photo: Paul Tyler)

Exposed sandy beach at Scarista - too rough for many burrowing animals

 Luskentyre-Seilebost beach (sheltered).jpgSheltered Seilebost Beach    (Photo: Paul Tyler)

More shelter at Seilebost means finer sand and better conditions for burrowing animals like cockles and lugworms

finsbay mud.jpgFinsbay    (Photo: Paul Tyler)

Extreme shelter together with river input produces a very fine sediment on this muddy shore at Finsbay. Rivers also carry organic debris to the sea. When the river meets the sea the water slows down allowing it to drop its suspended load. Seawater also makes the fine particles clump together which helps it settle out. This organic debris is also consumed by bacteria. In places where the mud is very fine and rarely disturbed, bacteria will consume all the oxygen in the mud as they feed on the organic material. That is why the mud is black and stinking just below the surface. Fine sand may also be black a few inches beneath the surface, where oxygen from the air or seawater is unable to reach the areas where the bacteria have used it all up. Some animals such as lugworms will munch their way through the bacteria-laden mud or sand, creating a flow of oxygen bearing water as they do so. Others, such as cockles, overcome the lack of oxygen beneath the surface by extending long breathing tubes (called syphons) to the surface.

Here are links to some of the animals you can find on our sandy and muddy shorelines:

Banded Wedge ShellBootlace WormCockleDog CockleFurrow ShellLugwormRayed Trough ShellRazorshellSandmason Worm


by Paul Tyler

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