Predators can exert nonconsumptive effects (NCEs) on prey expressed as reductions of feeding activity to minimize detection by predators. As such NCEs are common, there is a growing interest in determining if they can ultimately indirectly influence other species enough to alter community structure. This could be particularly the case when a predator's prey is a foundation species, as such organisms influence the abundance of many other species. We tested this hypothesis using a SE Pacific intertidal system consisting of a snail species (Acanthina monodon) that preys upon a mussel foundation species (Perumytilus purpuratus) that hosts several associated species (barnacles, other bivalves, and algae). First, we did lab experiments to investigate whether waterborne snail cues can trigger a reduction of the feeding rate of mussels, which are filter-feeders. Specifically, we evaluated NCEs on the rates of larviphagy (consumption of pelagic invertebrate larvae) and phytoplankton filtration. Then, we did a field experiment to investigate whether waterborne snail cues can alter the community structure of the main associated species that grow in mussel beds.
Results/Conclusions
The lab experiments revealed that waterborne snail cues effectively limited the larviphagy rate and phytoplankton filtration rate of mussels. In turn, the field experiment showed that waterborne snail cues led to higher abundances of associated barnacles and bivalves (expected under a model of lower larviphagy in the mussels) and a lower algal biomass on the mussels (expected under a model of fewer mussel excretion products due to lower feeding rates). Overall, our study shows for the first time that a predator can indirectly affect community structure through NCEs on a foundation species. Since animal foundation species are ubiquitous in benthic marine environments, predator NCEs on these organisms could help to better understand the unexplained variation that is often found in community structure in these systems.