Environmental Engineering Reference
In-Depth Information
Nature Conservancy Council visited several stretches of the shore during the late 1970s and considered
the area tobe ofprimary biological importance, and more recently the Countryside Council forWales has
carried out a comprehensive study of the intertidal area.
FIG 57. The extensive limestone platforms, known as 'huvvers and scarras', near Paviland. (Harold Grenfell)
the author for Figures
Thekeyspeciesofrockyshoreshaveaverticalzonation,whichproducesadistinctivebandedappear-
ance at low tide. A zone of lichens, a white barnacle zone and a zone of brown seaweeds dominate the
upper,middleandlowershorelevelsrespectively.Thebrownseaweedsarealsoseparated, thechannelled
wrack Pelvetia canaliculata being highest on the shore, followed by the spiral wrack Fucus spiralis , and
thenthebladderwrack Fucusvesiculosus .Theserratedwrack Fucusserratus istypicalofthelowershore,
while the lowest level of all is usually occupied by the oarweed Laminaria digitata . This pattern partly
reflects the different degrees of tolerance to desiccation and submergence shown by the various species.
The number of marine invertebrate species increases down the beach and barnacles and marine snails in-
cluding periwinkles, top shells, dog-whelks and limpets are typical of the mid-shore. On the lower shore,
these are joined by species less tolerant of desiccation such as sponges and sea firs. Various coastal birds
feed on rocky shores at low tide and at high tide their place is taken by coastal fish.
The upper shore, which is only covered during high spring tides, is dominated by extensive bands of
orange, grey and black lichens on the bedrock, with the orange lichen Caloplaca marina lying above a
band of black tar lichen Verrucaria maura and associated species such as V. amphibia (Fig. 58). Marine
animals characteristic of this zone, which hide in cracks and graze on the rocks, include the periwinkles
Melarhaphe neritoides and Littorina saxatilis . A speciality of the Glamorgan coast is the small white
woodlouse Metatrichoniscoides celticus ,whichlivesbeneathdeeplyembeddedstonesjustabovethehigh
tide mark. Although naturally overlooked to some extent it does appear to be quite rare and most of the
records are from the Gower cliffs. A few terrestrial insect species have also adapted to occupy air pockets
in rock crevices in the intertidal zone and the Gower shores contain the very small (2.5 millimetres long)
reddish-yellow ground beetle Aepus robini .
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