Two decades since first invasion: Revisiting round goby impacts on nearshore aquatic communities in the Upper St. Lawrence River

Abstract

Time Since Invasion (TSI) at invaded sites is an important factor that can moderate invasive species abundances and their ecological impacts on resident communities, and yet it remains rarely addressed by invasion studies. We revisit the ecological impacts of round goby invasion in the Upper St. Lawrence River (Canada) on macroinvertebrate and fish communities, by taking into consideration the effects of TSI since initial invasion 20 years ago. Our objectives were to: 1) test the effect of TSI and invasion status on round goby abundance, and 2) investigate the effects of TSI, invasion status, and round goby abundance on macroinvertebrate and fish communities. Round goby abundance displayed a strong positive relationship with TSI. Environmental conditions, especially substrate and water conductivity were found to reduce round goby TSI and characterize uninvaded sites and >12 years TSI sites. However, we detected first potential signals of a reduction in round goby abundance at sites with TSI of 17–19 years compared with sites having 13–16 years TSI which had similar environmental conditions. Nonetheless, round gobies continued to have enduring impacts on total macroinvertebrate diversity, even at sites with TSI of 17–19 years, likely as a result of ongoing predation. This observation was supported by a negative association of round goby TSI on the abundance of dominant macroinvertebrate taxa at sampling sites in the Upper St Lawrence River, as well as dietary stomach content data. The fish community was less sensitive to round goby TSI than macroinvertebrate communities.