title: Calcium interacts with temperature to influenceDaphniamovement rates.
abstract: Predicting the ecological responses to climate change is particularly challenging, because organisms might be affected simultaneously by the synergistic effects of multiple environmental stressors. Global warming is often accompanied by declining calcium concentration in many freshwater ecosystems. Although there is growing evidence that these changes in water chemistry and thermal conditions can influence ecosystem dynamics, little information is currently available about how these synergistic environmental stressors could influence the behaviour of aquatic organisms. Here, we tested whether the combined effects of calcium and temperature affect movement parameters (average speed, mean turning frequency and mean-squared displacement) of the planktonicDaphnia magna, using a full factorial design and exposingDaphniaindividuals to a range of realistic levels of temperature and calcium concentration. We found that movement increased with both temperature and calcium concentration, but temperature effects became considerably weaker when individuals were exposed to calcium levels close to survival limits documented for severalDaphniaspecies, signalling a strong interaction effect. These results support the notion that changes in water chemistry might have as strong an effect as projected changes in temperature on movement rates ofDaphnia, suggesting that even sublethal levels of calcium decline could have a considerable impact on the dynamics of freshwater ecosystems.
authors.affiliation: Department of Integrative Biology , University of Guelph , Guelph, Ontario , Canada N1G 2W1.
authors.forename: Gustavo S
authors.identifier: 0000-0003-0707-4128
authors.initials: GS
authors.lastname: Betini
authors.affiliation: Department of Integrative Biology , University of Guelph , Guelph, Ontario , Canada N1G 2W1.
authors.forename: Jordan
authors.initials: J
authors.lastname: Roszell
authors.affiliation: Department of Integrative Biology , University of Guelph , Guelph, Ontario , Canada N1G 2W1.
authors.forename: Andreas
authors.initials: A
authors.lastname: Heyland
authors.affiliation: Department of Integrative Biology , University of Guelph , Guelph, Ontario , Canada N1G 2W1.
authors.forename: John M
authors.initials: JM
authors.lastname: Fryxell
keywords: Daphnia magna; aquatic systems; climate change; diffusion; turn rates; velocity; zooplankton