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

The benthic fish assemblage of the soft-bottom community of the Duluth-Superior Harbor before and after round goby invasion (1989–2011)

Diets and Diet Overlap of Nonindigenous Gobies and Small Benthic Native Fishes Co-inhabiting the St. Clair River, Michigan

The invasive round goby Apollonia melanostomus (formerly Neogobius melanostomus) has negatively affected benthic fish communities throughout the Great Lakes. In this study, we compared the sensory physiology and behavior of three native species—slimy sculpin Cottus cognatus, spoonhead sculpin C. ricei, and logperch Percina caprodes—with those of the round goby to determine the mechanisms that allow the round goby to dominate native fish. The reaction and strike distances of the four species were examined during predator‐prey trials using natural amphipod prey Gammarus spp. under varying light intensities (0‐130 lx) to compare input from the mechanosensory lateral line and visual systems. Trials in the dark (0 lx) indicated that the sculpins and the round goby had similar lateral line sensitivity. However, all three native species had a significant advantage in reaction and strike distance over the round goby at higher light intensities. Interspecific resource competition was assessed by pairing a round goby with a native fish in an artificial stream. Round gobies gained significantly more weight than the native fishes during all trials. Slimy sculpins were able to maintain their weight in the presence of the round goby; however, spoonhead sculpins and logperch lost a significant amount of weight during the trials. These experiments indicate that although the round goby does not possess an inherent sensory advantage, it can dominate resources and outcompete native fish. Thus, round gobies may pose risks for a wide variety of native benthic fishes.

Relationships among round gobies, Dreissena mussels, and benthic algae in the south nearshore of Lake Ontario

Round goby (Neogobius melanostomus) population structure, biomass, prey consumption and mortality from predation in the Bay of Quinte, Lake Ontario

The Laurentian Great Lakes have been the site of numerous aquatic invasive species such as the sea lamprey, zebra mussel and round goby. To further understand interactions between invasive and native species in situ, competitive interactions between native logperch (Percina caprodes) and invasive round goby (Neogobius melanostomus) were examined using submerged enclosures in the Duluth‐Superior Harbour. Experiments were conducted on rocky or sandy substrate throughout the spring and summer months. Trials consisted of single fish, paired conspecifics or round goby/logperch pairs with weight change determined after 28 days. The round gobies were able to outcompete and/or negatively affect logperch on rocky substrates as a direct result of round goby/logperch interactions, as logperch fared well when round gobies were excluded from the enclosures. Although there is evidence that round gobies exclude logperch from rocky substrates, the logperch population remains close to pre‐invasion levels in the predominantly soft‐bottomed harbour. The continued coexistence of the logperch with the round goby is attributed to the vastly greater area of soft‐bottom vs. rocky substrate in the harbour, with the round gobies in the soft bottom younger and smaller than those in the rocky substrate. Recent evidence suggests that the round goby population is declining on the soft substrates indicating that the two populations will continue to coexist in the harbour.

Demography and substrate affinity of the round goby ( Neogobius melanostomus) in Hamilton Harbour

The round goby (Neogobius melanostomus) is a successful invader of the Great Lakes-St Lawrence River basin that harbours a number of local parasites. The most common are metacercariae of the genus Diplostomum. Species of Diplostomum are morphologically difficult to distinguish but can be separated using molecular techniques. While a few species have been sequenced from invasive round gobies in this study system, their relative abundance has not been documented. The purpose of this study was to determine the species composition of Diplostomum spp. and their relative abundance in round gobies in the St Lawrence River by sequencing the barcode region of cytochrome c oxidase I. In 2007-2011, Diplostomum huronense (=Diplostomum sp. 1) was the most common, followed in order by Diplostomum indistinctum (=Diplostomum sp. 4) and Diplostomum indistinctum sensu Galazzo, Dayanandan, Marcogliese & McLaughlin (2002). In 2012, the most common species infecting the round goby in the St Lawrence River was D. huronense, followed by D. indistinctum and Diplostomum gavium (=Diplostomum sp. 3). The invasion of the round goby in the St Lawrence River was followed by a decline of Diplostomum spp. in native fishes to low levels, leading to the previously published hypothesis that the presence of the round goby has led to a dilution effect. Herein, it is suggested that despite the low infection levels in the round goby, infections still may lead to spillback, helping to maintain Diplostomum spp. in native fishes, albeit at low levels.

Round Goby Neogobius melanostomus invasion of the Grand River (Ontario, Canada) presents an opportunity to assess the role of abiotic gradients in mediating the establishment and impact of nonnative benthic fishes in rivers. In this system, sequential low-head dams delineate uninvaded and invaded river reaches and create upstream gradients of increasing water velocity. We hypothesized that flow refugia created by impounded reservoirs above low-head dams enhance local Round Goby abundance. Round Goby influence on the native fish community was determined by variance partitioning, and we used generalized additive models to identify small-bodied benthic fish species most likely to be impacted by Round Goby invasion. Round Goby abundance declined as the degree of reservoir effect decreased upstream. The distributions of four species (including the endangered Eastern Sand Darter Ammocrypta pellucida) in invaded reaches were best explained by inclusion of both reservoir-associated abiotic variables and Round Goby abundance as model terms. To determine establishment potential of the uninvaded reach immediately upstream, four environmental habitat characteristics were used in discriminant function analysis (DFA) to predict three potential outcomes of introduction: non-invaded and either lower or higher Round Goby abundance (low and high invasion status, respectively) than the median number of Round Goby at invaded sites. Our DFA function correctly classified non-invaded and high-abundance invasion status sites > 85% of the time, with lower (73%) success in classifying low-abundance invasion status sites, and the spatial pattern of our results suggest that likelihood of establishment is greatest in impounded habitat.

The round goby (Neogobius melanostomus) is a fish native to the Ponto-Caspian region that is highly invasive through freshwater and brackish habitats in northern Europe and North America. Individual behavioural variation appears to be an important factor in their spread, for example a round goby's personality traits can influence their dispersal tendency, which may also produce variation in the behavioral composition of populations at different points along their invasion fronts. To further analyze the drivers of behavioral variation within invasive round goby populations, we focused on two populations along the Baltic Sea invasion front with closely comparable physical and community characteristics. Specifically, this study measured personality within a novel environment and predator response context (i.e., boldness), and directly analyzed links between individuals’ personality traits and their physiological characteristics and stress responses (i.e., blood cortisol and lactate, brain neurotransmitters). In contrast to previous findings, the more recently established population had similar activity levels but were less bold in response to a predator cue than the older population, which suggests that behavioral compositions within our study populations may be more driven by local environmental conditions rather than being a result of personality-biased dispersal. Furthermore, we found that both populations showed similar physiological stress responses, and there also appeared to be no detectable relationship between physiological parameters and behavioral responses to predator cues. Instead, body size and body condition were important factors influencing individual behavioral responses. Overall, our results reinforce the importance of boldness traits as a form of phenotypic variation in round goby populations in the Baltic Sea. We also highlight the importance of these traits for future studies specifically testing for effects of invasion processes on phenotypic variation in the species. Nonetheless, our results also highlight that the physiological mechanisms underpinning behavioural variation in these populations remain unclear.

Round Goby (Neogobius melanostomus) has invaded high diversity tributaries of the Laurentian Great Lakes, including those supporting multiple species of conservation concern. The extent and magnitude of ecological impacts on benthic riverine fishes is poorly understood, especially changes in diet overlap and feeding strategy. We used a before-after study design to examine the impact of Round Goby on native benthic riverine fishes, including the Threatened Eastern Sand Darter (Ammocrypta pellucida) in the Sydenham River, Ontario, Canada. To evaluate shifts in diet overlap and feeding strategy, fishes were collected with multiple gears and the direct (diet overlap with Round Goby) and indirect (diet overlap among native benthic fishes) impacts of Round Goby were assessed. Prior to the arrival of Round Goby, six ecologically significant diet overlaps occurred among the studied native benthic fishes; whereas, following arrival, 20 ecologically significant diet overlaps occurred, with 6 out of 8 species, including Eastern Sand Darter, showing significant, direct diet overlap with Round Goby. Fishes exhibiting significant diet overlap with Round Goby shifted feeding strategies to become more specialized, a change in feeding consistent with potential competitive effects. Although the long-term consequences of invasion-induced diet and feeding shifts remain poorly understood, increased competitive interactions suggested by diet overlap may be occurring between Round Goby and native benthic riverine fishes and may exacerbate the observed decline of native species.

Dietary habits of invasive Ponto-Caspian gobies in the Croatian part of the Danube River basin and their potential impact on benthic fish communities

River barriers such as hydropower dams and weirs can negatively affect river ecosystems by disrupting connectivity and reducing biodiversity. However, such barriers could also limit the spread of invasive species. Here, we used a spatial population genetics approach to test whether river barriers act as a hindrance to gene flow in the invasive round goby (Neogobius melanostomus Pallas, 1814). We sampled gobies from four different rivers across their invasive range in Central Europe (the Danube, Dyje, Morava, and Rhine rivers), with locations on either side of eight major river barriers. Using microsatellite genotyping, we found that round goby populations were differentiated with increasing number of river barriers and with increasing distance between sampling sites, depending on the river system in focus. We found significant population differentiation across three individual barriers, but no clear indication that this was related to barrier type as barriers were highly diverse. We also found reduced genetic diversity in populations that were more recently established. Our findings suggest that successive river barriers can sometimes slow the spread of round goby. Further research on the features of barriers that hinder round goby movement will help to design barrier passage solutions that will both limit spread of this invasive species and maintain connectivity for the native fauna.

Dry-weight energy density of prey fishes from nearshore waters of the upper Niagara River and Buffalo Harbor, New York

There is increasing evidence that parasitism represents an unpredictable dimension of the ecological impacts of biological invasions. In addition to the risk of exotic pathogen transmission, other mechanisms such as parasite-release, could contribute to shaping the relationship between introduced species and native communities. In this study, we used the Eurasian round goby (Neogobius menalostomus) in the Great Lakes-St. Lawrence River ecosystem to further explore these ideas. As predicted by the parasite-release hypothesis, recently established populations of round goby were parasitized by a depauperate community of generalist helminths (8 taxa), all commonly found in the St. Lawrence River. In comparison, two native species, the logperch (Percina caprodes) and spottail shiner (Notropis hudsonius), were the hosts of 25 and 24 taxa respectively. Round gobies from each of 3 sampled localities were also less heavily infected than both indigenous species. This is in contrast to what is observed in round goby’s native range where the species is often the most parasitized among gobid competitors. This relative difference in parasite pressure could enhance its competitiveness in the introduced range. However, our study of an older population of round goby in Lake St. Clair suggests that this advantage over native species could be of short duration. Within 15 years, the parasite abundance and richness in the round goby has more than doubled whereas the number of parasite species per fish has increased to levels of those typical of fish indigenous to the St. Lawrence-Great Lakes watershed.