Size Selectivity and Energy Maximisation of the Introduced Seastar, Aster/as Amurens/s (lotken), in Tasmania, Australia

The selectivity of the introduced north Pacific seastar, Asterias amurensis, for different sizes of prey was investigated with the aim of predicting the impact this species will have on the age structure ofnative prey species and, thus, on their survival. The energy maximisation capabilities ofA. amurensis were assessed. The time small A. amurensis (r= 56-77 mm) spent handling the mussel Mytilus edulis increased exponentially with increases in mussel size; handling time by large seastars (r= 78-86 mm) only increased when eating the largest mussels offered. Mussels ofthe size class 20-29 mm were preferred. The energy content ofsix mussel size classes was divided by the handling time ofeach to give a prey value. The optimal mussel size class was calculated to be 30-39 mm. Thus, A. amurensis was not shown to maximise its energy by consuming mussels of a size that would give the greatest energy return for the energy expended. Smaller seastars consumed a greater percentage of their body weights per day (4.970/0) than did larger seastars (2.570/0).