Salinization decreases population densities of the freshwater crustacean, Daphnia dentifera

Salinization of freshwater systems is a global concern. In the northern United States, a large driver of freshwater salinization is the application of road salt which runs into freshwater systems. We tested the effects of salinization on traits and population densities of the freshwater crustacean, Daphnia dentifera, a common species in the Midwestern United States. We first measured the effects of salinity on resource acquisition (feeding rates), birth rates, and death rates of individual D. dentifera. Then we performed an experiment to quantify the population-level effects of salinity. There was little effect of salinity on individual characteristics; birth and death rates were unaffected by salinity treatment and only one D. dentifera genotype showed lower feeding rates with increased salinity. However, D. dentifera population densities were lower with increased salinity. Our results suggest that studies conducted on individuals may underestimate the population-level effects of salinization. Moreover, since Daphnia are often dominant grazers in freshwater systems, reduced population densities from salinization could have dramatic effects on communities and ecosystems.