The impact of predation by Kelp GullsLarus dominicanus on the sub-Antarctic limpetNacella delesserti

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The Southern Kelp GullLarus dominicanus derives about 45% of the mass of its marine diet from the limpetNacella delesserti at 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 dominicanus seldom 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. delesserti.