This study examined the combined salinity and temperature tolerance of two marine bivalve molluscs,Perna viridisandMytella charruana, which have recently invaded the southeastern United States. It is essential to understand the role that these abiotic variables play in invasions and establishment of nonnative species. We simultaneously explored survival at three salinity ranges (5–9, 20–22.5, and 35–40 ppt) in both cold and warm water for juveniles and adults of both species. We determined thatPerna viridiscan survive at a wide range of temperatures (9–35°C) when the salinity is 35–37 ppt; however, as salinity decreased, the thermal survival range forP. viridisbecame narrower. WithM. charruana, our data suggest that juvenile and adult individuals can survive at a wide range of salinities (5–40 ppt) at 20°C, but the salinity tolerance range narrowed as the temperature decreased or increased. Additionally, we observed that temperature rapidly impacted survival ofP. viridisandM. charruana(within hours), while salinity impacts were more gradual (days to weeks). These data can be used to help predict successful introductions and future expansions ofP. viridisandM. charruanain introduced habitats.