Compound extreme events reshuffle the stacked odds in the gamble between native and introduced bivalves

Global climate change increasingly exposes intertidal ecosystems to extreme weather events, reshaping biodiversity patterns and altering community assembly dynamics. While many studies have examined the effects of individual stressors, few have explored the interactive impacts of multiple, co-occurring stressors on the comparative survival and establishment potential of native versus introduced species. The current study examines how simultaneous fluctuations in temperature and salinity affect the survival and burrowing behavior of two ecologically and economically important intertidal bivalves: the native Cerastoderma edule and the introduced Ruditapes philippinarum. Using a mesocosm experiment across four salinity levels and five temperature regimes, we found that R. philippinarum exhibited significantly lower mortality than C. edule at temperatures exceeding 35 degrees C, particularly under low-salinity conditions (10 and 20 PSU). In contrast, burrowing behavior did not differ significantly between the two species, suggesting that their ecological functions may persist despite differential survival. Our results show that compound stressors widen the mortality gap between native and introduced species more than single stressors alone. Integrating these findings with conceptual modeling and field data, we propose the concept of 'disturbance-driven establishing windows', critical periods during which compound extreme events preferentially facilitate the establishment of introduced species with broader environmental tolerance. These insights enhance our understanding of species turnover and community dynamics in intertidal ecosystems facing intensifying climate extremes.