The acquisition of sensory information is central to all species interactions. Such information is vital to individual decision-making, and the choices mediated by sensory information have consequences that shape populations, communities, and ecosystems. Most aquatic organisms use chemical cues to assess predation risk and other key ecological factors, but chemoreception may be disrupted in systems with elevated pH. Episodic elevation of pH is an increasingly common occurrence in lakes and ponds, and is usually associated with nutrient enrichment (eutrophication), especially in poorly buffered lakes and ponds. Here we present the results of laboratory and mesocosm experiments designed to test whether elevated pH impairs perception of predation risk by the freshwater snails Physa acuta and Helisoma trivolvis.
Results/Conclusions
In one set of experiments, nutrients were added to outdoor mesocosms, resulting in mid-afternoon pH values of 8.5 to 9.7. Both snail species responded strongly to sunfish cues when housed in water drawn from control mesocosms but showed no evidence of avoidance at the highest levels of enrichment. In both cases, predator avoidance was impaired at a pH > 9.0. In a laboratory study, we used buffers to establish six pH treatments ranging from 7.5 to 10.0. At lower pH Physa acuta responded to fish cues by moving into safer habitats, but avoidance became impaired at a pH of 9.4. Helisoma trivolvis also responded to fish at lower pH, and their avoidance behavior became impaired at a pH of 8.8. Thus, our results show that elevated pH associated with eutrophication can result in sensory impairment of aquatic animals, thereby linking the large-scale perturbation of biogeochemical cycles and the behavioral ecology of aquatic organisms. Given the diversity of aquatic organisms that depend on reception of chemical cues and the broad extent of eutrophication, chemosensory impairment as a result of eutrophication is likely a common occurrence in nature. Efforts to establish ecologically relevant thresholds for pollutants should account for perceptual impairment.
