Combined effects of predation, flow speed, and sub-lethal exposure to insecticide on the feeding behavior of a spionid polychaete

Abstract

Behavioral responses of infauna to predation have received limited study, especially in varying hydrodynamic conditions above estuarine sediments. Many estuaries also are impacted by chemical pollution, including runoff of terrestrial insecticides such as chlorpyrifos. We tested how feeding behaviors of a tube-dwelling, interface-feeding worm, Polydora cornuta, change due to predation by an omnivorous estuarine fish, Fundulus parvipinnis, in the contexts of hydrodynamic regime and sub-lethal exposure to chlorpyrifos. We performed two experiments in a laboratory flume at two flow speeds (6 or 15 cm s−1). We analyzed feeding behaviors of P. cornuta when F. parvipinnis were either actively feeding on the worms, caged upstream to prevent predation, or absent from the flume. In our first experiment, the presence of actively feeding F. parvipinnis reduced the time P. cornuta spent feeding by half relative to when fish were absent. Fish caged upstream had no effect on worms' feeding activity, indicating that P. cornuta reduced their feeding in response to tactile stimuli or sensing light shadows, rather than chemical alarm cues. Our second experiment tested the effects of actively feeding F. parvipinnis on the feeding behaviors of P. cornuta that had undergone a 96-h exposure to chlorpyrifos. Worms exposed to chlorpyrifos reduced feeding relative to unexposed worms, but only in the absence of predatory fish. Flow speed also influenced worms' behavior, with worms preferentially suspension feeding at the faster flow. In both experiments, individual worms that were observed to be attacked by F. parvipinnis resumed feeding approximately 10–11 min after the attack. The combined results demonstrate that the close proximity of actively feeding fish has a consistently greater effect on the feeding behavior of an infaunal polychaete than does sub-lethal exposure to a toxicant or variation in water flow.