The Southern Kelp GullLarus dominicanusderives about 45 of the mass of its marine diet from the limpetNacella delessertiat sub-Antarctic Marion Island. It selectively feeds on the largest limpets (35–65 mm) —a pattern most obvious in adult gulls — and eliminates about 19.6 of these limpets per year in the intertidal zone and in shallow waters, thus accounting for about 50 of the known annual mortality of limpets of this size. The gulls cannot forage for limpets in water more than 40 cm deep, and in the intertidal zone boulder-fields provide the limpets a refuge against the gulls. The gulls are also selective in feeding most often on limpets with pale shells. This alters the colour composition of limpet populations in habitats where predation is most intense.Larus dominicanusseldom feeds on limpets on the mainland of South Africa, and only on small limpets, probably because a greater range of food is available, but possibly also because the limpet species that occur on South African shores attach with forces that are three to six times those ofN. deles
展开▼
