Ardea
Official journal of the Netherlands Ornithologists' Union

login


[close window] [previous abstract] [next abstract]

Hockey P.A.R. & Branch G.M. (1984) Oystercatchers and limpets: impact and implications. A preliminary assessment. ARDEA 72 (2): 199-206
At rocky seabird islands in the south-western Cape, South Africa, the upper intertidal zone often is characterized by large beds of macroalgae which are conspicuously absent at nearby mainland localities. These beds are believed to be, at least in part, a product of heavy predation by African Black Oystercatchers Haematapus maquini on the upper shore limpet Patella granularis. Densities of limpets in sites accessible to oystercatchers are reduced to the point where the limpets no longer control algal growth by the grazing of algal sporelings. Both limpet and algal growth rates are faster at islands than on the mainland, and the establishment of high shore macroalgal beds, with their associated invertebrate fauna, facilitates the feeding of smaller wading birds. By virtue of their faster growth rate and larger size, an appreciable proportion of the limpets at islands is too large for oystercatchers to prey upon. Since gamete output in limpets is proportional to size, it is these large limpets (which account for up to 86% of the total gamete release) that provide the key to population maintenance in the presence of high predation pressure. Recruitment to the limpet population is guaranteed, regardless of predation pressure on smaller size classes. These observations have important implications for the conservation-management of intertidal invertebrate resources.


[close window] [previous abstract] [next abstract]