Ecology of Patella species from the Cape peninsula,South Africa. IV. Desiccation

The importance of desiccation as of factor limiting zonation was investigated for 7 South African Patella Linnaeus species. Small specimens lost water fastest and were least tolerant to desiccation. Differences in shell shape largely explain differences in the rate of desiccation, both within and between species: tall conical shells with a small mouth circumference minimize water loss. Tolerance was closely related to zonation, but zonation was not correlated with either shell shape or rate of water loss. Two groups of limpets could be distinguished: migratory species which increase in tolerance as they age, correlated with the habit of moving up the shore; and non-migratory species which have a narrow range of tolerance. Zonation of the former group is probably limited by physical factors while the latter are behaviourally restricted to a narrow zone. The selective value of these strategies is discussed.