Climate change is reshaping coastal ecosystems through gradual warming and increasingly frequent extreme heat events, potentially affecting native and introduced species differently. We experimentally compared the native marine snail Littorina obtusata, a habitat and dietary specialist, to the introduced generalist Littorina littorea under sustained warming and short-term extreme heat. We measured survival and performance metrics, including grazing, growth, and attachment strength, under short- and long-term thermal stress in air and water. L. littorea consistently outperformed L. obtusata, maintaining or increasing function under warming and exhibiting greater survival during simulated heatwaves. Conversely, L. obtusata showed performance declines and higher mortality. Consistent with studies of other introduced species, generalist traits, including environmental tolerance and flexible resource use, support invasional success and may promote resilience under gradual and extreme climate stress, as observed for L. littorea in this study. As climate change intensifies, introduced species possessing traits that promote resilience may lead to greater dominance and restructuring of ecological communities.