Environmental determinants of round goby invasion refuges at a river scale: implications for conservation of native biodiversity

Introductions of exotic invasive species are a global disturbance for natural habitats. The severity of invasions can greatly vary from local to global scales, as observed in invasion refuges, exhibiting lower-than-expected invasion intensity. In this study, we analyzed the effects of water conductivity and wetland presence on the density of the round goby (Neogobius melanostomus) in a large-scale study (> 1300 sites), spanning a 400 km stretch of the St. Lawrence River (Canada). Our results showed that round goby density was null in sites with water conductivity under 100 µS/cm and increased toward a probable biological optimum at 300 µS/cm. The presence of wetlands appeared to also decrease round goby density along the conductivity continuum. Similarly, fish community diversity was maximal outside of the round goby water conductivity optimum. Hence, low water conductivity (<100 µS/cm), in interaction with the presence of wetlands, can provide a refuge for native aquatic species, establishing a simple risk assessment tool for managers. Our results also highlighted the high value of wetland conservation for conservation of native species biodiversity.