Effects of osmotic stress on predation behaviour of Asterias rubens L.

• We studied changes in behaviour and performance of Asterias rubens in response to decreased salinity.
• Changes in salinity resulted in mortality, decrease of performance and feeding rate. However acclimation occurred.
• We discuss the ecological implications of these effects in this important mussel predator.

Environmental stress plays an important role in determining ecosystem functioning and structure. In estuarine areas both tidal and seasonal salinity changes may cause osmotic stress on predators, affecting their behaviour and survival. The interaction between these predators and their prey may affect performance, thus influencing predator impact on prey populations. The common starfish, Asterias rubens, inhabits estuarine areas, such as the Dutch Wadden Sea, that exhibit large seasonal variation in salinity (10–32 PSU). In those areas A. rubens exerts top down control on its prey, thus representing an important shellfish predator. This predation may impact on cultured and natural shellfish populations. However, the effects of osmotic stress on A. rubens performance may influence its effect on prey. Although the effect of salinity in A. rubens survival has been extensively studied, the impact on its predation behaviour and acclimation capacity remains unclear. In this study, we analyse the performance of A. rubens preying on mussels (Mytilus edulis) after a salinity decrease and monitor its acclimation capacity over a period of 22 days. Our experiments demonstrated that salinity affected performance by reducing feeding activity and altering size prey selection. Moreover, as acclimation occurred, A. rubens predation performance improved in all sub-lethal treatments. We conclude that osmotic stress caused by decreasing salinity potentially influences A. rubens distribution, abundance, and potential impact on prey populations. However the magnitude of the change in salinity (from 31 to a minimum of 10 PSU) and its timescale (3 weeks) mediate this effect.