Complex demographic, developmental, fitness, and physiological responses of larval eastern hellbenders to elevated water conductivity

Elevated water conductivity, driven by human‐induced ion inputs, has been implicated in the population declines of many freshwater organisms. Eastern hellbenders ( Crytobranchus alleganiensis alleganiensis ) have suffered range‐wide declines, with elevated conductivity proposed as a major contributor, particularly for early life stages. However, the mechanisms through which conductivity affects hellbenders at these early life stages remain poorly understood. We experimentally assessed the effects of chronic exposure to elevated conductivity (1000 μS cm −1 ) on wild eastern hellbender larvae over 91 days posthatching, as well as the effects of switching between low conductivity (100 μS cm −1 ) and high conductivity after 30 days of exposure. Chronic high conductivity resulted in ~50% higher larval—but not egg—mortality compared to low controls. Larvae switched from low to high conductivity experienced a ~17% increase in mortality compared to their unswitched counterparts, whereas those switched from high to low conductivity exhibited a ~25% decrease in mortality compared to those that remained in high. Chronic exposure to elevated conductivity reduced body mass and altered morphology, with similar effects observed in animals switched from low to high conductivity. Conversely, switching animals from high to low conductivity only marginally improved growth and did not fully compensate for initial deficits. Despite altered size and morphology, locomotor performance was unaffected. Whole‐body cortisol, a measure of stress, and lipid peroxidation, a marker of oxidative stress, did not differ across treatments. Collectively, these results indicate that elevated conductivity can contribute to hellbender population declines through both lethal and sublethal effects. Future work should focus on the ecological consequences of increased ion concentrations for population persistence.