Environmental patterns of establishment and early-stage impacts from invasive round gobies in an aquatic biodiversity hotspot

Quantifying the establishment, spread, and impacts of invasive species requires an accurate understanding of ecosystem structure and function before and after introductions. In 2014, the round goby (Neogobius melanostomus) invaded the LeBoeuf Creek subwatershed of French Creek, a tributary to the Allegheny River, PA, USA. We report on a decade of stream monitoring within the immediate invasion front by describing the environmental conditions associated with round goby populations and the potential impacts and resource overlap with native fish communities. First, we found no evidence of a round goby population increase since invasion, and that round goby population densities were higher during early summer and in closer proximity to Lake LeBoeuf. Second, the presence of round gobies overlapped substantially with environments of low-oxygen conditions, low native fish richness, and macroinvertebrate communities dominated by non-insect taxa, all of which are representative of lentic environments. In contrast, greater aquatic insect diversity corresponded to higher native benthic fish diversity of uninvaded reaches. Finally, there was no evidence that round gobies have induced any changes to the native fish communities within the invasion front during the past decade. While our results have indicated a relatively localized invasion from round gobies with minimal impacts to the stream habitats of French Creek, the greatest impacts are likely to be in lentic habitats near Lake LeBoeuf, where round goby populations are most established.