Classical views of trophic cascades emphasize the consumptive effects of predators on their prey and emergent indirect predator effects on basal resources (density-mediated indirect interactions, DMIIs). However, it is increasingly clear that non-consumptive predator effects on prey traits can also lead to powerful indirect effects on lower trophic levels (trait-mediated indirect interactions, TMIIs). Such trait-mediated cascades are quite common in aquatic systems and emerge because prey exhibit anti-predator behaviors in response to waterborne chemical cues signaling increased predation risk. These chemicals are transported between predators and prey by flowing water and are thus subject to hydrodynamic forces (e.g. turbulence) that can alter chemical signal structure and the chemoreceptive abilities of a predator-prey species pair. Hence, the effects of turbulence on chemoreception may strongly influence the relative importance of DMIIs and TMIIs depending on how such effects influence the ability of predators to find prey and the ability of prey to avoid being consumed. The primary goal of this research is to examine how flow effects on the sensory capabilities of both predators and prey influence the nature and strength of indirect effects. Drs. Smee and Trussell will explore this issue with laboratory and field experiments on a tri-trophic, rocky inter-tidal food chain containing the predatory green crab (Carcinus maenas), an intermediate consumer (the carnivorous snail, Nucella lapillus), and one of this snail's principal food resources (the barnacle, Semibalanus balanoides). Previous work has shown that both DMIIs and TMIIs can operate within this food chain and there is good evidence from other systems that hydrodynamic regime can strongly influence the chemoreceptive abilities of crab predators and their prey. The following questions are central to the project: 1. How do hydrodynamic forces influence the responses of Nucella to green crab risk cues? 2. How do hydrodynamic forces influence green crab foraging behavior and success? 3. How do hydrodynamic forces shape the nature and strength of trophic cascades in the field? The results of the research will provide a novel link between the effects of hydrodynamic regime on predator-prey chemical signaling and indirect predator effects that often play a pivotal role in the structuring of natural communities. The research project will provide training for three graduate students, one postdoctoral fellow, and several undergraduate students. in the collaborative project involving Texas A&M, Corpus Christi (TAMUCC) and Northeastern University. Students will experience a rich interdisciplinary research environment that blends expertise in chemical ecology, hydrodynamics, and community ecology.
