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The Seashore

Rocky Shore Trail
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The upper shore (sheltered shores)

A close-up of an upper shore community

A close-up of an upper shore community with Channel Wrack at the top, a small amount of Twisted Wrack at the bottom; Rough Perwinkles and Limpets.

For our purposes we are taking this zone as the bit of the shore between the highest tides (extreme high water spring tides (EHWS)) and the mean height of neap tides (MHWN). Do remember that we are using these heights as a convienience, the organisms on the shore may not understand this. They may therefore have the temerity to survive where we say they shouldn't.

PROBLEMS:

Lichens are still in evidence on the upper shore. They are a symbiotic association between a fungus and an alga. The fungus possesses thick cell walls to reduce water loss and can store water (up to 3 times its own weight) as well as food produced by the algae. Lichens however can be thought of as terrestrial organisms that are tolerating being immersed in seawater. Fewer kinds of lichen survive on the upper shore than in the splash zone. The most obvious is the black tar lichen (Verrucaria maura) which occurs as a distinctive black band along the top of the shore. People who have not visited Dale Fort or this web-site have been known to mistake it for black oil. In truth it does not look like most peoples conception of a living organism, people are often astonished to find out that it's a living thing. In this zone you should find rough periwinkles and just below it some barnacles. Seaweeds begin to make an appearance at this level notably the brown seweeds channelled wrack (Pelvetia canaliculata), twisted wrack (Fucus spiralis). On sheltered shores a small red alga (seaweed and alga mean the same thing) Catenella caespitosa often occurs. It's never aquired a common name and it's unusual among red seaweeds because most of them find conditions on the upper shore very difficult. (You can find out more by clicking the hyperlinks).

Marine animals begin to appear in greater numbers and variety on the upper shore. Limpets (Patella vulgata) and rough periwinkles are snails that graze on the algae and lichens. Barnacles are shelled crustaceans (like lobsters and crabs) which filter their food from the water and are found towards the bottom of this zone. Animals in this zone have to be able to withstand desiccation and most of them do this most obviously by posession of a shell. The soft bodied beadlet anemone (Actinia equina) may be found in suitable microhabitats like moist crevices. There are lots of other interesting ways of coping with the stresses of this zone that you can find out about by clicking on the links.

Compare with zone (upper shore) with the exposed shore zone.

Table of Zones - click to go

 


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