Temperature thresholds to guide choice of freshwater species for monitoring onset of chronic thermal stress impacts in rivers

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Aquatic species show different sensitivities and responses to chronic thermal stress, resulting in varying degrees of resistance to the negative impacts of climate change, which are ultimately expressed as range expansions or contractions. The choice of species appropriate for assessing climate change impacts in aquatic ecosystems should be guided by the robustness of the relationship between a chosen chronic stress thermal threshold and associated habitat contraction. Twelve aquatic species were evaluated as potential climate change indicators, from which six were selected for testing a conceptual framework for predicting the degree of utility of a species as a climate change indicator. Results indicate that species with a chronic biological thermal threshold below 20°C are likely to experience in excess of 50% loss of thermally suitable environment. Cooler thermal thresholds could inform the choice of suitable sentinel species for use as early indicators of chronic thermal stress, while thresholds above this reflect increasingly thermally resistant species within aquatic communities.