Environmental modification of chemosensory interactions between predators and prey: The world according to whelks

The effect of environmental modification of predator sensory abilities remains largely unknown, despite the importance of predators to ecosystem function. I conducted a series of experiments to investigate effects of hydrodynamics on the chemosensory search behavior and foraging success of two species of marine gastropods, knobbed whelks (Busycon carica) and channeled whelks (B. canaliculatum). This research consisted of laboratory studies of navigational performance in turbulent odor plumes, as well as field studies that related in situ patterns of foraging success to turbulent mixing.; Laboratory and field tests showed that whelks are effective foragers in turbulent flow. The search success of both whelk species was unaffected by changes in flow velocity and turbulence, whereas search efficiency (tracking speed, orientation towards the source) increased in the most turbulent conditions tested. Manipulative field experiments demonstrated the ecological consequences of whelk foraging proficiency in turbulent environments. When deployed in tidal channels, baited traps that increased turbulent mixing of bait odors captured twice the number of channeled whelks as unmodified control traps. Experimental plots of clams subjected to elevated turbulence experienced a 43% increase in knobbed whelk predation compared to unmodified control plots. The magnitude of turbulent mixing also alters the importance of nonlethal predator effects by reducing prey responses to predation risk. Avoidance responses to predator odor normally protect clams from consumers, but increased turbulence around clam plots exposed to predator cues counteracted avoidance responses of clams and resulted in increased whelk predation. Detailed flow measurements in the field indicated that background levels of turbulence may mediate the impact of hydrodynamics on chemosensory interactions between whelks and their prey. Collectively, this research suggests that slow-moving predators can continue foraging in turbulent conditions that are known to diminish the olfactory abilities of faster taxa, even when prey animals are given advance warning of a predatory threat. Environmental factors affecting animal sensory abilities can change the outcome of chemically mediated interactions and possibly could result in resource partitioning along a gradient of turbulence intensity. Further examination of diverse sensory strategies should help to refine expectations of predator-prey interactions in a variety of systems.