Nonconsumptive predator effects on prey demography: dogwhelk cues decrease benthic mussel recruitment

Predators often have nonconsumptive effects (NCEs) on prey behaviour, but the demographic consequences for prey remain poorly known. This is important to understand because demography influences the functional role of a species in its community. We used an intertidal predator-prey system to investigate predator NCEs on prey recruitment, a key demographic process for population persistence. Pelagic mussel larvae are known to avoid waterborne cues from dogwhelks, which prey on intertidal mussels. Through a field experiment done in Atlantic Canada, we manipulated the presence of dogwhelks in intertidal habitats during the mussel (Mytilus spp.) recruitment season. We measured mussel recruitment in collectors that could be reached by waterborne dogwhelk cues but not by dogwhelks themselves. We found that the nearby presence of dogwhelks significantly decreased mussel recruit density. A previous study done in the same habitats under the same experimental conditions showed that dogwhelk cues also limit the recruitment of barnacles, another prey item for dogwhelks. However, such NCEs were stronger than those observed for mussel recruitment, possibly because mussels have more opportunities to escape predation during their benthic existence. Thus, basic features of natural history might be useful to predict the intensity of predator NCEs on prey recruitment.