Water motion modulates predator nonconsumptive limitation of prey recruitment

Predator chemical cues can elicit behavioral changes in prey to minimize predation risk. Recent field studies have shown that such predator nonconsumptive effects (NCEs) can ultimately affect prey demography. The environment is known to modulate predator consumptive effects on prey demography, but the environmental modulation of predator NCEs on prey demography remains unstudied. We investigated this knowledge gap using an intertidal predator-prey system. Dogwhelk (Nucella lapillus) chemical cues can limit barnacle (Semibalanus balanoides) recruitment by limiting larval settlement. As waves disperse chemicals in coastal environments, we experimentally tested the hypothesis that wave exposure limits dogwhelk NCEs on barnacle recruitment. Shortly before the barnacle recruitment season of 2013 (May-June), we established cages in rocky intertidal habitats in Atlantic Canada under two levels of wave exposure. The cages were used to manipulate the presence and absence of dogwhelks. At the center of each cage, we installed a tile where barnacle pelagic larvae could settle and develop into recruits. Mesh prevented caged dogwhelks from accessing the tiles, but allowed their waterborne cues to reach the tiles. Data collected at the end of the recruitment season indicated that dogwhelk cues limited barnacle recruitment in wave-sheltered habitats but had no effect on recruitment in wave-exposed habitats. These findings suggest that predicting predator NCEs on prey demography may require environmental information related to the ability of prey to locate predators.