Round Goby

The Ponto-Caspian round goby (Neogobius melanostomus, Pallas 1814) most probably was established in the Gulf of Gdańsk, Baltic Sea, in the late 1980’s and has since become one of the dominant species in the region. In this study we assess the role of round gobies as prey for two important fish species in the Gulf of Gdańsk, cod (Gadus morhua) and perch (Perca fluviatilis). We compared their present diet with stomach analyses from the area prior the round goby establishment, as well as with diet analysis from Baltic regions where round gobies are absent. There were large differences in the diet between cods from the Gulf of Gdańsk 2003–2006 compared to cods in earlier studies (1977–1981) from the Southern Baltic Sea. There were also large differences in cod and perch diets from areas with and without round goby. Presently, round goby constitutes the most important prey for medium sized cods in Gulf of Gdańsk, and perch from the same area almost exclusively feed on gobiids. Stomach analysis, trophic level estimates, and stable isotope analyses all indicated that cod and perch in Gulf of Gdańsk after the round goby establishment belonged to a similar trophic level. Beside round goby, no mussel feeding fish contributed much to the diet of cod or at all to the diet of perch. Thus, it is likely that round gobies constitute a new energetic pathway from mussels to top predators. However, due to the short time elapsed after round goby establishment, we can only speculate on the species future impacts on Baltic food webs.

Recent invasion theory has hypothesized that newly established exotic species may initially
be free of their native parasites, augmenting their population success. Others have hypothesized
that invaders may introduce exotic parasites to native species and/or may become hosts to native parasites
in their new habitats. Our study analyzed the parasites of two exotic Eurasian gobies that were
detected in the Great Lakes in 1990: the round goby Apollonia melanostoma and the tubenose goby Proterorhinus
semilunaris. We compared our results from the central region of their introduced ranges in
Lakes Huron, St. Clair, and Erie with other studies in the Great Lakes over the past decade, as well as
Eurasian native and nonindigenous habitats. Results showed that goby-specific metazoan parasites were
absent in the Great Lakes, and all but one species were represented only as larvae, suggesting that adult
parasites presently are poorly-adapted to the new gobies as hosts. Seven parasitic species are known to
infest the tubenose goby in the Great Lakes, including our new finding of the acanthocephalan Southwellina
hispida, and all are rare. We provide the first findings of four parasite species in the round goby and
clarified two others, totaling 22 in the Great Lakes—with most being rare. In contrast, 72 round goby
parasites occur in the Black Sea region. Trematodes are the most common parasitic group of the round
goby in the Great Lakes, as in their native Black Sea range and Baltic Sea introduction. Holarctic trematode
Diplostomum spathaceum larvae, which are one of two widely distributed species shared with Eurasia,
were found in round goby eyes from all Great Lakes localities except Lake Huron proper. Our study
and others reveal no overall increases in parasitism of the invasive gobies over the past decade after
their establishment in the Great Lakes. In conclusion, the parasite “load” on the invasive gobies appears
relatively low in comparison with their native habitats, lending support to the “enemy release
hypothesis.”

The aim of the present study was to perform a pilot assessment and analysis of the oxidative stress (OS) level in four commercially important fish species (round goby, red mullet, sprat and horse mackerel) from different localities of the Bulgarian Black Sea coast. The fish were sampled during trawl selectivity experiments. The OS level in the fish was assessed by measuring lipid peroxidation (LPO), glutathione concentration (GSH), activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST), as well as acetylcholine esterase (AChE) in gills and liver. Round goby and red mullet caught in the Nessebar Bay showed clear signs of OS with the highest levels of LPO and GST activities, accompanied by the lowest AChE activities in both liver and gills. On the contrary, round goby caught near Maslen Nos (a region with good ecological conditions) were least affected by OS with low LPO and high GSH concentrations and SOD activity. There were no significant differences in the OS bioindicators of horse mackerel from the different localities. Sprat caught in Nessebar Bay, compared to those caught from the other localities, showed presence of OS indicated by lower GSH levels and relatively higher CAT, GPx and GST activities, accompanied by low AChE activity in gills. It can be concluded that round goby and red mullet were more vulnerable to OS induced by marine environmental factors than the horse mackerel and sprat. However, their antioxidant defense system allows them to tolerate and adapt to the environment of their habitats. Further studies are needed for the assessment of OS in important fish species in the Bulgarian part of the Black Sea.

ntroductions of non-indigenous species (NIS) are considered a major threat to aquatic ecosystems worldwide. While it is valuable to know the distributions and ranges of NIS, predictive spatial models along different environmental gradients are more useful for management of these species. In this study we modelled how external drivers and local environmental conditions contribute to the spatial distri- bution of an invasive species using the distribution of the round goby Neogobius melanostomus in the Baltic Sea as an example. Using the collected distribution data, an updated map on the species distri- bution and its invasion progress in the Baltic Sea was produced. The current range of the round goby observations is extensive, covering all major sub-basins of the Baltic Sea. The most recent observations appeared in the northern regions (Northern Baltic Proper, the Gulf of Bothnia and the Gulf of Finland) and on the eastern and western coasts of southern Sweden. Modelling results show that the distribution of the round goby is primarily related to local abiotic hydrological conditions (wave exposure). Furthermore, the probability of round goby occurrence was very high in areas in close proximity to large cargo ports. This links patterns of the round goby distribution in the Baltic Sea to shipping traffic and suggests that human factors together with natural environmental conditions are responsible for the spread of NIS at a regional sea scale.

The trophic roles of key Ponto-Caspian invaders (quagga mussels Dreissena bugensis, amphipods Echinogammarus ischnus and round goby Apollonia melanostomus) within the littoral food web of eastern Lake Erie were quantified using stable isotopes (δ13C, δ15N). A dual stable isotope parameter search with a mass balance component was used to assess the isotopic importance of quagga mussels and amphipods as dietary items to two size classes of round goby. The utility of the mass balance simulation was also evaluated as a tool to approximate isotopic contributions of feasible prey and identify gaps incurred by “missing” prey items not included in the sampling. The mass balance dietary simulation, confirmed by stomach content data, indicated that isotopically important prey to small round goby (< 11.2 cm) were chironomids and Ponto-Caspian amphipods, while large round goby (≥ 11.2 cm) showed strong preference for quagga mussels. The dietary mass balance simulation output also supported the isotopic importance of round goby to the somatic growth of smallmouth bass, rock bass and freshwater drum. The isotopic mass balance output for yellow perch was more ambiguous, which may be in line with their known broadly omnivorous diet. The white bass output was in line with published data indicating increasing consumption of round goby for this species, while the brown trout output strongly favoured alewife isotopic contributions. However for white perch and walleye, the mass balance simulations were not in line with their known published diets in Lake Erie, probably due to a lack of key prey items in the sample set (e.g. zooplankton for white perch and shiner species for walleye). As expected, the Ponto-Caspian species have integrated themselves into the littoral food webs, and the “quagga mussel–round goby–smallmouth bass” food chain forms one of the key components within the trophodynamics of Lake Erie.

The Eurasian round goby (Neogobius melanostomus) invaded the freshwater North American Great Lakes in
~1990 via accidental introduction from ballast water discharge. Its genotypes in the Great Lakes traced to estuaries
in the northern Black Sea, where the round goby flourishes in a variety of salinities to 22 parts per
thousand (ppt). To prevent further introductions, U.S. and Canadian Coast Guard regulations now require
that vessels exchange ballast water at sea before entering the Great Lakes. Since salinity tolerance of the invasive
round goby population is poorly understood, we tested 230 laboratory-acclimated fish in three experimental
scenarios: (1) rapid salinity increases (0–40 ppt), simulating ballast water exchange, (2) step-wise
salinity increases, as during estuarine tidal fluxes or migration from fresh to saltwater, and (3) long-term survivorship
and growth (to 4 months) at acclimated salinities. Almost all gobies survived experiments at
0–20 ppt, whereas none survived ≥30 ppt, and at 25 ppt only 15% withstood rapid changes and 30% survived
step-wise increases. Ventilation frequencies were lowest at 10–15 ppt in step-wise experiments, in conditions
that were near isotonic with fish internal plasma concentrations, reflecting lower energy expenditure
for osmoregulation. Growth rates appeared greatest at 5–10 ppt, congruent with the larger sizes reached
by gobies in Eurasian brackish waters. Thus, we predict that the Great Lakes round goby would thrive in
brackish water estuaries along North American coasts, if introduced. However, oceanic salinities appear
fatal to the invasive round goby, which likely cannot withstand complete seawater ballast exchanges or oceanic
habitats.

Population genetic structure and systematic relationships were investigated for two exotic
fishes introduced to the Great Lakes in 1990, the round goby Neogobius melanostomus and the tubenose
goby Proterorhinus marmoratus, using DNA sequences from the left domain of the mitochondrial DNA
control region. Samples of round gobies were compared from different sites in the Great Lakes, an introduced
population from the Gulf of Gdansk in Poland, and a native population from the northern Black
Sea. The round goby was characterized by relatively high genetic variability, and 17 haplotypes were
identified from 64 individuals. Levels of genetic variation for the round goby were similar in the invasive
and native sampling sites, suggesting relatively large founding populations and lack of bottlenecks. The
northern Black Sea was eliminated as a probable founding source for both the Great Lakes and the exotic
population in Poland. Substitutions in the left domain of the control region revealed significant differences
among samples from the Great Lakes and Eurasia, and between Lakes Erie and St. Clair, suggesting
non-random mating. No variation was detected in the tubenose goby population in the Great Lakes,
which has been less successful in terms of spread and population growth. A molecular clock calibration
suggested that the genera Neogobius and Proterorhinus diverged about 5.2 ± 1.0 million years ago,
apparently separating from a common ancestor shared with Gobius during the isolation of the Paratethys
basin from the Mediterranean Tethys Sea.

The round goby (Neogobius melanostomus) first invaded North America in 1990 when it was discovered in the St. Clair River. Despite more than 15 years of potential invasion, many Great Lakes’ lotic systems remained uninvaded. Recently, we captured the round goby from several Great Lakes tributaries known as species-at-risk hotspots. With a combination of field sampling of round gobies and literature review of the impact of round gobies on native taxa, we assess the potential impacts of the secondary invasion to native species using three mechanisms: competition; predation; and indirect impacts from the loss of obligate mussel hosts. We estimate that 89% (17/19) of benthic fishes and 17% (6/36) of mussels that occur in these systems are either known or suspected to be impacted by the secondary invasion of round goby. In particular, we note that the distribution of potential impacts of round goby invasion was largely associated with species with a conservation designation, including seven endangered species (1 fish, 6 mussels). As these recent captures of round goby represent novel occurrences in high diversity watersheds, understanding the potential impacts of secondary invasion to native biota is fundamental to prevent species declines and to allow early mitigation.

The potential of predators to regulate populations of dreissenid mussels (Dreissena polymorpha and Dreissena rostriformis bugensis) has been addressed since early in the dreissenid invasion of North America. Round gobies (Neogobius melanostomus) larger than approximately 60mm have been shown to prey extensively on dreissenids, whereas smaller round gobies feed mainly on aquatic insects and crustaceans. We propose that ontogenetic changes

The geographic range of an invasive species is a key determinant of relative impact in the invaded region. Comparison of invasive species that are widespread or rare in invaded ranges can highlight mechanistic traits that determine the risk of impact from invasion. Round Goby (Neogobius melanostomus) is more geographically widespread and abundant than Tubenose Goby (Proterorhinus semilunaris) across invaded ranges of the Laurentian Great Lakes. We used stable isotopes of carbon (δ13C) and nitrogen (δ15N) in liver and muscle to contrast the isotopic niche breadth and niche plasticity of Round Goby and Tubenose Goby near the inflow and outflow of Lake St. Clair and in western Lake Superior. At all sites, Round Goby and Tubenose Goby that matched in size (21 – 53 mm standard length) had distinct isotopic niches with no overlap, driven by higher δ15N in Round Goby. The variation in isotopic niche, and the mean difference in δ13C and δ15N between muscle and liver, was greater for Round Goby, suggesting both greater seasonal shifts in diet and niche plasticity in this more widely established invader. Round Goby that were significantly larger than Tubenose Goby had broader isotopic niches and greater niche plasticity in the majority of cases and this was associated with isotopic niche overlap with smaller Round Goby and Tubenose Goby. Our findings suggest that a broad and plastic isotopic niche provides scope for wider establishment range in invasive fish species.

Biological invasions comprise accidental evolutionary experiments, whose genetic compositions underlie relative success, spread and persistence in new habitats. However, little is known about whether, or how, their population genetic patterns change temporally and/or spatially across the invasion's history. Theory predicts that most would undergo founder effect, exhibit low genetic divergence across the new range and gain variation over time via new arriving propagules. To test these predictions, we analyse population genetic diversity and divergence patterns of the Eurasian round goby Neogobius melanostomus across the two decades of its North American invasion in the Laurentian Great Lakes, comparing results from 13 nuclear DNA microsatellite loci and mitochondrial DNA cytochrome b sequences. We test whether 'genetic stasis', 'genetic replacement' and/or 'genetic supplement' scenarios have occurred at the inva-sion's core and expansion sites, in comparison with its primary native source population in the Dnieper River, Black Sea. Results reveal pronounced genetic divergence across the exotic range, with population areas remaining genetically distinct and statistically consistent across two decades, supporting 'genetic stasis' and 'founder takes most'. The original genotypes continue to predominate, whose high population growth likely outpaced the relative success of later arrivals. The original invasion core has stayed the most similar to the native source. Secondary expansion sites indicate slight allelic composition convergence towards the core population over time, attributable to some early 'genetic supplementation'. The geographic and temporal coverage of this investigation offers a rare opportunity to discern population dynamics over time and space in context of invasion genetic theory vs. reality.