Co-operative prey capture and unusual brooding habits of Anasterias rupicola (Verrill) (Asteroidea) at sub-Antarctic Marion Island

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Abstract
The asteroid A. rupicola and the limpet Nacella delesserti dominate shallow-water communities around sub-Antarctic Marion Island; the limpet is the most important prey species for the starfish. A. rupicola can feed solitarily but often feeds in aggregations, particularly on large prey. This cluster-feeding allows it to capture prey otherwise unattainable because of their size, a fact of particular importance for smaller starfish. N. delesserti reaches a size where it is immune to predation by solitary starfish but even the largest limpets can be captured and consumed by starfish groups. Thus co-operative prey capture overcomes the normal prey size limits. A. rupicola also broods its eggs and young and is unusual in feeding on prey while still carrying brooded young. These unusual features may be related to the extremely isolated nature of the starfish''s habitat, to its very slow growth and high longevitiy, and to its low incidence of brooding.