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A salty landscape of fear: responses of fish and zooplankton to freshwater salinization and predatory stress


Predator–prey relationships are altered by anthropogenic contaminants. Road salt is a widespread contaminant among freshwater ecosystems, yet a relatively understudied subject in community ecology. Unknown is whether road salt salinization interacts with predatory stress to influence the growth, behavior, or reproduction of freshwater organisms. Using rainbow trout (Oncorhynchus mykiss) and zooplankton (Daphnia pulex), we exposed them to variable levels of road salt (NaCl) crossed with the presence or absence of alarm cues or kairomones. Alarm cue reduced trout activity and aggression and increased shoaling behavior. Road salt reduced trout growth in the high compared to moderate salt concentration, but neither concentration was different from the control. There was no interaction between alarm cues and salt for trout. Road salt and predatory stress had an additive effect on Daphnia abundance. Predatory stress decreased Daphnia abundance by 11%. Compared to the control, salt decreased Daphnia abundance by 40% in 860 mg Cl/L and 79% in 1300 mg Cl/L, and by the final day abundance was reduced by 85% in 1300 mg Cl/L. Road salt and predatory stress had an interactive effect on Daphnia reproduction. Predatory stress in control water and moderate salt levels (230 mg Cl/L) increased sexual reproduction of Daphnia, but these responses disappeared at high salt concentrations. Thus, road salt could limit reproductive adaptations to natural and anthropogenic stressors in Daphnia. Our results indicate road salt salinization could alter zooplankton population dynamics directly and by interacting with predatory stress, which might affect energy flow through freshwater food webs.

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We thank Jeff Inglee of the Warren County Fish Hatchery for providing experimental fish. This study was funded by the Jefferson Project at Lake George, a collaboration between Rensselear Polytechnic Institute, IBM, and The Fund for Lake George. We also thank Brian Mattes for culturing zooplankton and Justin Rappold, Jeevan Narendran, Skylar Carter, and Alex Brooks for their help setting up and taking down the experiments.

Data availability statement

The datasets during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Author contribution statement

WDH and RAR conceived and designed the experiments. WDH performed the experiments and analyzed the data. WDH and RAR wrote the manuscript.

Correspondence to William D. Hintz.

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Communicated by Joel Trexler.

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Hintz, W.D., Relyea, R.A. A salty landscape of fear: responses of fish and zooplankton to freshwater salinization and predatory stress. Oecologia 185, 147–156 (2017).

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  • Community interactions
  • Deicing
  • Land use
  • Road salt
  • Sub-lethal effects