Wave action and starvation modulate intra-annual variation in displacement, microhabitat selection, and ability to contact prey in the common sea star, Asterias rubens Linnaeus

Abstract

The common sea star, Asterias rubens, is a major predator in the rocky subtidal zone in the northern Gulf of St. Lawrence and along the Atlantic coast of Newfoundland, Canada. Knowledge about the ecology of A. rubens in these highly seasonal systems is largely limited to studies of interspecific competition for prey. Two experiments in an oscillatory wave tank were used to test the hypothesis that wave action and starvation modulate displacement, microhabitat selection, and ability to contact mussel (Mytilus edulis) prey in A. rubens from southeastern Newfoundland. Both experiments were carried out in two seasons (winter and summer) to quantify intra-annual variation in the effects of wave action (three wave velocities: null [0.0ms−1], low [0.1ms−1], and high [0.2ms−1]) and starvation (two levels: fed and starved three weeks). Experiment 1, in which two sea stars were allowed to displace and make contact with six microhabitats typifying natural seabed heterogeneity, showed that A. rubens displaced up to 50% less with increasing wave velocity. Displacement was 120% higher in summer than winter and lower in starved than fed individuals in summer only. The sea star predominantly stayed on flat horizontal surfaces, did so more frequently in the presence than absence of waves, and spent more time in the two most uneven microhabitats in winter than summer regardless of wave velocity. Experiment 2, in which one sea star in the centre of a depression was allowed to move to the top of surrounding mounds, showed that more sea stars that left the centre of the depression reached the top of the mounds in summer than winter, in the absence than presence of waves, and when starved than fed. Sea stars that reached the top of mounds spent more time there in the presence than absence of mussels in summer only, when starved than fed in summer only, and in the presence than absence of mussels at null and low wave velocities. Measurements of wave height, sea temperature, and A. rubens abundance over six months at one subtidal site indicated that the sea star was >4 times more abundant at 8m than at 2m and 4m. This difference was unrelated to temperature and likely mainly caused by the wave environment. Collectively, results demonstrate that wave action, and to a lesser extent starvation, are key modulators of the inclination and ability of A. rubens to explore its environment and localize prey. In southeastern Newfoundland, the response of A. rubens to wave action and starvation is adaptable, being generally stronger in summer than winter, when sea temperature is markedly lower.