Subtle changes in prey foraging behavior have ­cascading effects in a shallow estuary

Abstract

Direct consumption of prey and the effect of predator intimidation on prey behavior are recognized determinants of food web structure, but our understanding of the mechanisms that cause behavioral cascades (trait-mediated indirect effects, TMIE) are lacking, especially for larger, mobile species. Mechanisms of TMIE were measured by both continuous in situ monitoring (via telemetry) of predator (red drum Sciaenops ocellatus) and prey (blue crab Callinectes sapidus) behavior and resource (hard clam Mercenaria mercenaria) mortality with and without structure (artificial sea- grass). The presence of a predator significantly reduced the mortality of the resource (TMIE), but the TMIE was not affected by the presence of seagrass. The behavioral results indicated that the red drum did not significantly reduce the blue crab's overall movement or habitat domain but did reduce the prey's ability to optimally forage on clam patches. The mechanisms of TMIE were disruptions of short time periods of high prey activity. Our findings highlight subtle mechanisms of TMIE that could be overlooked if qualitative and not quantitative behavioral measurements are conducted. These qualitative results have implications for interpretations of previous TMIE studies as well as risk taking models.