John Wiley & Sons, Ltd.

Legacy of road salt: Apparent positive larval effects counteracted by negative post‐metamorphic effects in wood frogs

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Road salt runoff has potentially large effects on wetland communities, but is typically investigated in short‐term laboratory trials. We investigated effects of road salt contamination on wood frogs (Rana sylvatica) by combining a field survey with two separate experiments. The field survey tested whether wood frog larval traits were associated with road salt contamination in natural wetlands. As conductivity increased, wood frog larvae were less abundant, but those found were larger. In the first experiment, we raised larvae in outdoor artificial ponds under four salt concentrations and measured larval vital rates, algal biomass and zooplankton abundance. Salt significantly increased larval growth, algal biomass, and decreased zooplankton abundance. In the second experiment, we raised larvae to metamorphosis in the presence and absence of salt contamination and followed resulting juvenile frogs in terrestrial pens at high and low densities. Exposure to road salt as larvae caused juvenile frogs to have greater mortality in low‐density terrestrial environments, possibly due to altered energy allocation, changes in behavior or reduced immune defenses. Our study suggests low concentrations of road salt can have positive effects on larval growth yet negative effects on juvenile survival. These results emphasize the importance of testing for effects of contaminants acting through food webs and across multiple life stages as well as the potential for population‐level consequences in natural environments. This article is protected by copyright. All rights reserved

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