Limpet erosion of chalk shore platforms in southeast England

Abstract

Where the Upper Chalk reaches the coast in East Sussex it gives rise to high cliffs and wide shore platforms. Limpets (Patella vulgata) living on the platforms contribute significantly to platform downwearing by ingesting chalk as they graze and by excavating hollows (homescars) to which they return after feeding. A series of experiments has been carried out to try to estimate rates of limpet erosion. Analyses of the calcium carbonate content of the faeces of captive limpets suggest that adult limpets consume about 9 g of chalk per year. On the platforms as a whole limpets are probably responsible for an average of about 15 mm of surface lowering a year, but in areas of high population density the rate may be as high as 49 mm a year. The overall mean rate of platform lowering caused by all processes of weathering and erosion is estimated to be about 3 mm a year across the entire intertidal zone, but where limpets are present in significant numbers the rate may be around 3 mm a year. The implication is that limpets are responsible for an average of about 12 per cent of the downwearing in the areas they frequent, and in areas of maximal population density may cause 35 per cent or more of the downwearing in their vicinity. Subsidiary experiments are described that assess the limitations of the faecal method of estimating limpet erosion.