With increasing water temperatures and altered precipitation patterns in coastal systems due to climate change, there is an increasing need to understand the environmental tolerances of coastal species and how they will respond to future habitat conditions. It is also necessary to understand the variation in environmental tolerance across a species’ range in order to predict the broader impacts of climate change. In this study, the physiological effects of elevated temperature and lower salinity were assessed for juvenile hard clams, M. mercenaria, sampled from six populations ranging from Massachusetts to North Carolina. For each population, metabolic rate was measured using respirometry across four elevated temperature (27.5°C, 30°C, 32.5°C, and 35°C) and three lower salinity (20, 15 and 10) conditions. The treatment levels selected are representative of current and future conditions projected for Chesapeake Bay, VA. Mortality was also assessed at an environmentally relevant, elevated temperature (36°C). Preliminary analysis showed differences in temperature-related mortality rate among the six populations. The variations among these populations illustrate that the effects of climate change on hard clams will not be uniform and that some populations are more susceptible to environmental change than others. These results can help predict the future success of this species and its commercially important stocks, as well as provide insight for the aquaculture industry about the potential for breeding more resilient broodstock lines.