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

Predators have often been shown to 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 impact 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 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 four times stronger than those observed for mussel recruitment. This difference relates well to the higher ability of mussels to escape predation, as mussels can relocate while barnacles cannot. Therefore, basic features of natural history may be useful to predict predator NCEs on prey recruitment.