Freshwater bioindicators demonstrate sensitivities to potential changes from climate and mineral development in...

In Bristol Bay, Alaska, headwater streams support the world's largest, most valuable sockeye salmon fishery, but face an uncertain future due to climate change and proposed development. We used a framework based on pre-impact data to identify sensitive taxa and evaluate their potential as freshwater bioindicators for climate change and mineral development in the relatively undisturbed Lime Hills ecoregion of Bristol Bay. We identified sensitive taxa as those associated with distinct stream physical habitat types and those with published sensitivities to expected changes from climate or mineral development (e.g., increasing temperatures, acidity, conductivity, sedimentation, or general pollution). Using a 12-year dataset of stream macroinvertebrates and diatoms, we also investigated patterns over time in community composition and taxa presence. We identified five fish, 23 macroinvertebrate, and 26 diatom bioindicators with high interannual persistence in Bristol Bay wadeable streams that are also sensitive to either habitat change or future stressors. Stream benthic community composition has shifted over the past 12 years for both macroinvertebrates and diatoms, but we found few trends in individual taxa. The final bioindicator list can be used to measure future changes in stream habitats and communities of the Lime Hills ecoregion. Our framework used baseline data that captured both spatial and temporal variability in sensitive taxa and has utility for other pristine subarctic ecosystems prior to potential impacts.