Predator-prey interactions of Pugettia gracilis (Dana, 1851) and Leptasterias spp. (Verrill, 1866) and two species of Lacuna (Turton, 1827)

Abstract

This study focused on the predator prey interactions of two predators, the crab Pugettia gracilis, and sea stars of the genus Leptasterias and two low intertidal / shallow subtidal zone herbivorous snails, Lacuna vincta and Lacuna variegata. L. vincta and L. variegata graze on macroalgae, including Ulva spp.and Saccharina sessile, as well as microalgae such as diatoms that occur on the eelgrass Zostera marina. The feeding rates of P. gracilis and Leptasterias spp. on these two species of Lacuna were determine by in lab experiments, which included no choice and preference experiments. We found that P. gracilis ate significantly more L. variegata per unit time than Leptasterias and that the two predators had the same feeding rate on L. vincta. In choice tests P. gracilis preferred L. variegata. Seastars showed no preference. Neither predator was size selective and the size of the predator did not have a meaningful impact on the number of eaten snails or the size of snails eaten. The vulnerability of Lacuna vincta and Lacuna variegata in eelgrass and macroalgae habitats in the presence of the two predators was tested through mesocosm experiments. Because of the low recapture rate in controls, we were unable to detect significant differences in feeding of the two predators on the two species of Lacuna in the two habitat types.