Effects of temperature, body size, and starvation on feeding in a major echinoderm predator

Abstract

The common sea star, Asterias rubens, is a major predator in rocky subtidal ecosystems in the northern Gulf of St. Lawrence and along the Atlantic coasts of Nova Scotia and Newfoundland, Canada. We carried out two laboratory experiments to test the effects of water temperature, starvation, and body size, on mussel (Mytilus edulis) consumption and size selection in A. rubens from southeastern Newfoundland. Experiment 1 examined rates of consumption of medium (15–30 mm) mussels by small (9–15 cm) sea stars fed or starved moderately (for 3 weeks) at three temperatures representative of late summer highs (8, 11, and 15 °C) and one temperature representative of late winter lows (2 °C). Temperature and starvation did not affect consumption in summer, which was two times higher than in winter. Starvation also did not affect consumption in winter. Experiment 2 examined consumption of small (5–15 mm), medium, and large (30–45 mm) mussels by small and large (25–30 cm) sea stars fed or starved moderately or severely (for 6 weeks). Small sea stars consumed similar proportions of mussels regardless of starvation. However, large, moderately starved sea stars consumed at least two times more mussels than large, fed and large, severely starved individuals, indicating that the need to feed after a short starvation was higher in large than small A. rubens. Consumption of small, medium, and large mussels was, respectively, affected by the sea star’s size only, size and starvation independently, and size and starvation interactively. Collectively, our findings indicate that starvation, body size, and their interaction are key modulators of feeding in A. rubens, while suggesting that feeding is adaptable to thermal conditions. They also speak of the importance of considering the interplay between organismal traits and ongoing changes in ocean climate to better predict causes and consequences of alterations in predator–prey interactions.