Increasing prevalence of the non-indigenous round goby, Apollonia melanostomus, in coastal wetlands of the Laurentian Great Lakes: Are wetlands really resistant to invasion?

The round goby, a relatively recent benthic invader of the Laurentian Great Lakes, has altered existing food web relationships and has been shown to adversely affect the early life histories of several fishes. Previous literature suggests that round goby prefer rocky substrate and that soft-bottomed coastal wetlands may be resistant to their invasion. It is critical to determine whether or not round goby will invade coastal wetlands since wetlands are utilized by over 90% of Great Lakes fishes for some aspect of their life histories. Here we examine fish assemblage data from three types of coastal wetlands throughout Lake Michigan, Lake Huron, and the upper St. Lawrence River from 2002 to 2008 to identify the extent of the round goby invasion. Though the rate and extent of invasion differed among systems, nearly all wetlands examined (n = 69 sites) contained round goby by 2008 and relative abundance often exceeded 10% of all fish sampled.  Contrary to a density-dependent hypothesis of wetland use, there was an inverse relationship between abundance in wetlands and in nearby open-lake habitats. Overall, our results fail to support the larger hypothesis that all wetlands are resistant to round goby invasion.