The Effects Of Limpet Grazing On Algal Colonisation Around The Coast Of Holy Island (Anglesey)

Owens, Marguerite Wendy (1984). The Effects Of Limpet Grazing On Algal Colonisation Around The Coast Of Holy Island (Anglesey). MPhil thesis The Open University.



Limpets are common on exposed shores where they are generalist feeders of algal sporelings and mature plants. They are known to he responsible for the paucity of algal cover on exposed shores. The cyclic relationship which may exist between algae and limpets is probably partly controlled by the degree of exposure of the shore.

Five experimental areas differing in aspect and degree of slope, were chosen on the exposed rocky shore of the West coast of Holy Island (Anglesey). The experimental areas were cleared of limpets to allow algal colonisation to take place. Adjacent control areas were however not cleared of limpets and grazing continued in these areas. Any changes in algal composition in both experimental and control areas were monitored by using quantitative methods.

The pattern of recolonisation and algal succession on sheltered shores as described by previous workers, such as Jones (1946) was confirmed. Algal zonation occurred on almost all experimental areas and there was no strong evidence for zone mixing as described by Lodge (1948). Some alteration in the distribution of certain members of the Rhodophyceae indicated increased moisture levels on the rock surface as a result of recolonisation.

There was also some evidence of greater species diversity on the experimental areas compared with the control areas. Algal composition however, remained virtually unchanged in the control areas even after three years of study.

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