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The Seashore

Rocky Shore Trail
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The middle shore (exposed shores)

A view of the upper and middle shore of an exposed shore (B.E.S.3).

A view of the upper and middle shore of an exposed shore (B.E.S.3). Note the dark patches of Lichina pygmaea and the white barnacles.

We are taking the part of the shore between the average high water neap tide (MHWN) and the average low water neap tide (MLWN) as the middle shore. As we move down the shore the quantity and variety of living organisms begins to increase. The middle shore shows this big time, particularly towards the lower end of it.

Environmental conditions on the middle shore are more favourable for the majority of inter-tidal organisms. The middle part of an exposed shore is subject to heavy wave action and is bathed in strong sunlight for much of the day. It is also facing into the prevailing wind which makes it dry faster. Unlike sheltered shores we would not expect many seaweeds. These would be encrusting forms and small, quick growing opportunists in rock pools.

Large surface areas will be a no-no if you want to stay attached to the rock. Instead of seaweed look out for another lichen: Lichina pygmaea is a bit weird and looks like a fine, fuzzy mat found in small patches amongst the barnacles. Amongst the Lichina you can find a small community of very small organisms like the pseudo-scorpion and a bivalve, Lasaea.

The middle parts of exposed shores are often dominated by species which are capable of holding on tight against the wave action and withstanding the heat of the sun and the drying of the wind. Limpets and barnacles are two such creatures and they sometimes dominate the middle parts of exposed shores. Limpets are herbivores so there must be some seaweed or lichen for them to eat. Presumably juvenile algae settle (from the plankton) but get eaten before we can see them. The shore is immersed for a much greater % of the year (50-80% below mid-tide level) providing more food and feeding time for filter feeders like barnacles and mussels. Carnivores like the dogwhelk (Nucella lapillus) may now be found in sheltered microhabitats (cracks and crevices) feeding on the dense assemblages of barnacles (or sometimes mussels if there are any).

Compare this zone (middle shore) with one from a sheltered shore.

Table of Zones - click to go


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