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The Seashore

Sandy and Muddy Shores

Remember the singer back in the 1960's? Puppet on a String, and reached number 1 in the charts and first in Eurovision - sorry bit of trivia there, but that was Sandy Shore. Meanwhile back on the beach.....

Sediment depositing on an exposed shore

Sediment depositing on an exposed shore (Druidstone Haven, Pembroskeshire).

From the introduction it should be clear than sandy shores have larger grains and as a consequence tend to be cleaner as the sea washes through the spaces. Muddy shores, with their finer sediment, have smaller interstitial spaces and these trap organic matter. Smaller spaces means that drainage when the tide drops is less and so muddy shores hold on to their water. Hence we see a really important difference between the two shores: animals living on sandy shores will be subjected to greater desiccation.

Mud accumulates in very sheltered areas and may occur in patches on rocky shores, especially in the lower shore. Sand may be deposited in similar places but will also get deposited on exposed, shallow shores.

Solva, Pembrokeshire

Sediment accumulating within the shelter of a harbour (Solva, Pembrokeshire).

Sandy shores have a drier upper shore and wetter lower shore than muddy ones. This will produce a zonation although it can only be seen by digging up the species. Here are some of the issues and abiotic features:

•  surface of the upper shore dries at low tide (drainage through sand)

•  substrate is relatively unstable compared with rocky shores

•  no substrate for attachment

•  no shelter and so animals have to burrow to remain on the shore

•  no seaweeds present for food; microscopic detritus, diatoms and bacteria in spaces

With care the likely zonation that you can find on a sheltered sandy shore will have two or three zones. Amongst the strandline will be sandhoppers like Talitrus. Ragworms can be found in the upper shore, moving actively around in search of prey like the lugworm whose castes should be visible on the surface. Other sedentary worm like the red threads Audouinia sp colour the sand. Lower down diversity increases as it has less desiccation. On the surface the crown of tentacles of the sand mason are visible. This sedentary worm produces a long tube deep into the sand within which it lives. Cockles have a short siphon and so lie very close to the surface and can get easily disturbed. Another bivalve is the Tellin shell and these maybe found in quite exposed sandy shores as, with the long siphons, are able to survive deeper in the sediment. At the extreme low water marks will be razor shells and burrowing echinoderms, the sea potato.

Exposed sandy shores will have even fewer species because of the disturbance by the turbulent water. Donax is a bivalve able to survive this as it can quickly re-burrow and escape predators.

Mud, deposited in calm conditions, will be a flatter habitat (hence the term mudflat) and water is unlikely to drain. This minimal desiccation negates much in the way of zonation on the shore. However, the diversity of species is likely to be higher than sand. Smaller creatures will be commonplace.

Mud, deposited in calm conditions

 


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