Widespread calcium (Ca) decline in freshwater lakes is an emerging legacy of regional acidification. Lake surveys reveal that Ca declines correlate with dramatic changes in key herbivores, yet direct causal relationships had not been assessed for zooplankton communities. Shakira Azan (PhD) and Alex Ross (MSc) conducted the first field experiments to directly test whether declines in aqueous calcium cause reduced growth rates of crustacean zooplankton (Azan and Arnott 2017, 2018, Arnott et al. 2017). We found that copepods and Ca-poor cladocera, taxa once thought to be resistant to Ca decline, suffered reduced population growth under low Ca. Laboratory experiments conducted by MSc student, M. Overhill, were the first to investigate genotype-specific responses of Daphnia pulex, and revealed strong intraspecific variation and non-linear responses to Ca. These unexpected results were supported by a field experiment conducted by NSERC-USRA awardee, Amelia Cox, where anti-predator defenses of daphniids were diminished at intermediate Ca, but strong at low and high Ca concentrations (Cox et al. 2018).