Non-consumptive effects of predators on oysters differ based on predator identity and duration (but not frequency) of exposure

Abstract

Prey commonly encounter multiple predator species in interactions that vary in duration and frequency, yet these factors are rarely simultaneously considered in studies of non-consumptive effects. To consider these effects, we placed eastern oysters Crassostrea virginica in close proximity to crown conchs Melongena corona, blue crabs Callinectes sapidus, or both predators simultaneously in a field experiment for 0, 1, 3 consecutive, 3 isolated, or 6 consecutive days wk-1. Predator effects after 20 d were negligible. After 91 d, exposure to conchs led to significant decreases in oyster linear shell growth and mass and increases in shell thickness. The magnitude of these effects generally increased with the duration of exposure. Simultaneous exposure to both predators amplified these effects despite the fact that exposure to crabs alone did not significantly impact measured oyster traits. We also observed no difference in responses if oysters were exposed to predators 3 consecutive or 3 isolated days wk-1. Our results suggest that the non-consumptive effects of predators on oysters increase with exposure duration but that these effects may attenuate quickly after predators leave an area. Our findings also highlight the need to consider how predator community composition may impact non-consumptive effects. Prey may be more likely to respond to the presence of some predators when they are encountered simultaneously with other predators or in the presence of other stressors.