Ecotoxicology of salinity tolerance in Daphnia pulex: interactive effects of clonal variation, salinity stress and predation

Despite decades of research on the impacts of salinity in freshwater systems, the effects of salinity stress on planktivore-zooplankton interactions have received limited attention. We used laboratory-based experiments to examine Daphnia pulex responses to salinity stress and the lethal and non-lethal effects of Chaoborus (a dominant planktivore in fishless ponds). We also examined how D. pulex clonal variation mediates these responses using two clones known to differ in salinity tolerance. Presence of kairomone induced neckteeth formation, increased fertility and increased age and size at maturity relative to controls. As predicted, increasing salinity generally weakened life history responses to kairomone and reduced survivorship in the presence of lethal predation. While some of our results are suggestive of a moderating effect of clonal variation in salinity tolerance, clone effects on responses to increasing salinity were inconsistent. Our study demonstrates that non-lethal levels of salinity stress have the potential to impact Daphnia populations negatively by altering life history and behavioral responses to predators.