The goal of this study was to describe the benthic community and the food habits of the round goby Neogobius melanostomus, and to compare these food habits to the available prey observed in southeastern Lake Michigan. Nematodes and chironomid larvae were the most abundant organisms within the benthic samples, composing 22.4% and 17.2% of the total organisms collected respectively. Diet contents were identified, enumerated, and measured volumetrically. Copepods (35.7%) were the most abundant prey consumed, while chironomid larvae accounted for 30.5% of the total prey items. However, by volume, chironomid larvae composed 57.6% of the round goby diet, while zebra mussels Dreissena polymorpha composed 19.3%. The round goby were actively feeding on a variety organisms, but were selecting for certain prey. Diet and benthic community comparisons were also made with previous studies in the Great Lakes, which showed a difference in the dominant prey of the round goby as well as a decline in the abundance of zebra mussels in southeastern Lake Michigan. / Department of Biology

No description available.

No description available.

No description available.

No description available.

No description available.

<p>Animal movement has had a long history of study in the fields of behavioural ecology and toxicology, but rarely is the ecological context of behaviour in toxicology directly addressed. To explore how movement might be influenced by both sex differences and habitat contamination, I conducted studies on the round goby, an invasive fish, in a highly polluted part of Lake Ontario. In the first half of my dissertation I examined the reproductive biology of this species, finding evidence of multiple male reproductive tactics, and extended this to predict sex differences in goby movement. I showed that male fish were more exploratory in the laboratory, and over multiple years moved further in the field than females. This difference may predict variation in sex ratio along a round goby invasion front. Second, I accumulated multiple lines of evidence for contaminant exposure in these fish, validating their utility as a contaminant sentinel species in the field. With the same battery of behavioural tests, I revealed that round goby collected from cleaner sites were more exploratory than fish from highly contaminated sites in the laboratory, but moved similar distances in the field. Although changes in activity level are the most frequently used behavioural measure of contaminant exposure, the ecological relevance of change was not apparent in this study. These results challenge the utility of movement as an integrated biomarker of contaminant exposure beyond the laboratory.<strong></strong></p> / Doctor of Philosophy (PhD)

Invasive species are distributed all over the world and defined as organisms that have been introduced to a specific geographic area where they were not originally native. Such species have the ability to change the invaded ecosystem by for example competing with native organisms for limited food resources or occupying habitats with resulting environmental impacts. Therefore, knowledge about the characteristics of these invasive species as well as of the affected habitat types are very relevant to understand arising changes for endemic biodiversity and ultimately to protect it. For several large rivers in Germany, the round goby Neogobius melanostomus (Pallas 1814), a benthic fish species of Ponto-Caspian origin, represents a highly invasive fish species. In this thesis, I traced the invasion stage by conducting a literature research on the distribution pathways and documenting occurrence spots of N. melanostomus within two large rivers in Germany, the Elbe and the Oder. Within the Elbe River I determined the invasion front by applying electrofishing and environmental DNA (eDNA) analysis. This kind of knowledge enabled the results on diet composition gained from gut content and trophic niche width gained from stable isotopes (δ13C and δ15N) to be linked with the ongoing invasion stage. I found a bimodal distribution for N. melanostomus, from upstream and downstream. On examination of the downstream-directed invasion gradient, differences in N. melanostomus food composition as well as macroinvertebrate occurrence could be identified, with habitat structure and abundance being key determinants. Furthermore, N. melanostomus from sites invaded earlier exhibited the widest trophic niche size and individuals from the most recently invaded sites showed smaller niche sizes, most probably due to stronger competition for resources. Within the Oder River I focused on the competitive feeding interaction of N. melanostomus with the native fish species burbot (Lota lota). The main findings revealed that both fish species consumed preferred the same prey taxa (Crustacea, mainly Gammaridae) indicating potentially high competitive interactions for invertebrates. Whereas isotope ratios revealed a potential shift in the L. lota food web at the invaded site, represented by an enrichment of ẟ15N in muscle tissue and ẟ13C in liver tissue. This is indicative for a niche differentiation among both fish species.This thesis provides new insights into intra- and interspecies-specific impacts of N. melanostomus on riverine ecosystems under natural conditions, considering traceable invasion stages.:Table of contents 1 Abstract 3 Zusammenfassung 5 General introduction 7 Biological invasions: their introduction, dispersal and establishment 7 Application of environmental DNA to detect aquatic invasive species 10 The effects of invasive species on river food webs 10 Study Species: Round goby (Neogobius melanostomus) 12 Place of origin and spread 12 Round goby characteristics 13 Round goby feeding behaviour and effects on food webs 14 Round goby impacts on native fish species 15 Thesis Objectives 16 CHAPTER I 18 Tracing the colonization process of non-native gobies into a large river: the relevance of different dispersal modes 18 CHAPTER II 33 Diet compositions and trophic niche differentiation of Neogobius melanostomus along an invasion gradient in a large lowland river 33 CHAPTER III 54 Round goby (Neogobius melanostomus) impacts on diet composition and isotopic niche of native burbot (Lota lota) within the large Lowland River Oder, Germany. 54 General discussion 71 Factors influencing the invasion success of round goby 71 The importance of early invasion patterns 75 Invasion-induced alteration of riverine food webs 77 Challenges in the study of riverine invasions 80 Suggestions for research actions 82 Conclusion 85 References 86 Appendix 106 Chapter I 106 Chapter II 109 Danksagung 113 Selbstständigkeitserklärug 115

Biological invasions are a major threat to biodiversity world wide with annual economic costs up to 1.4 trillion dollars. The round goby (Neogobius melanostomus) is a particularly fierce invader that threatens ecological function of the Baltic Sea. Individual variation in behavioral traits that remain constant through time and context have been identified as crucial factors for explaining different parts of the invasion process. For example, asocial behavior facilitates dispersal from high density populations and comes with fitness benefits in low conspecific density. The latter is especially relevant, in an invasion context, following the initial colonization of a novel environment when population density usually is low. This thesis investigates the role of individual variation in phenotypic traits on species invasions. The main focus is on the effects of sociability, activity and boldness, but also including aggression and physiological stress tolerance, on dispersal tendency and selection at invasion fronts. To do this, we studied four round goby populations in the Baltic Sea, two of the most recently established and two of the oldest populations. In 2012 we demonstrated that asocial, active and bold round gobies are overrepresented at invasion fronts. Two years later we showed that dispersal from the new populations was led by individuals with high activity levels, while in all populations larger individuals dispersed. We also determined the length of the socalled lag-phase, between colonization and spread, in both newly established populations. The end of the lag-phase is hypothesized being triggered by high population density in the harbors leading to dispersal and subsequen colonization of the surrounding areas by small asocial individuals. In our final experiment, we present evidence of stress coping styles in round gobies, in which more aggressive individuals are also more stress tolerant and vice versa. Though we found no connection between stress coping and population age, we found that mortality was unaffected by population density and that the gobies became more aggressive and stress tolerant when kept in high density. To conclude, we have shown that: 1) individuals with high levels of activity, boldness and asociality are common at invasion fronts; 2) a lag phase occurs between colonization and spread in round goby invasions; 3) asocial individuals drive the spread from high density populations at the invasion front and; 4) round gobies adapt to high densities with high aggression and stress tolerance.

This study is a multidisciplinary approach to Species Distribution Modelling (SDM) where predictive models have been developed regarding the current distribution and potential spread of two invasive species found in Baltic Sea waters. Invasive species in the Baltic have long been an ecological and economic problem and the two species studied are well known for their adaptability in colonization and detrimental effects on local ecology all over the world. First, the Round Goby (Neogobius Melanostomus) has been steadily colonizing the Swedish Baltic coastline since 2008, the impact of which on local ecosystems is not fully understood. Also, the Chinese Mitten Crab (Eriocheir Sinensis), found in Swedish waters since the 1930’s, has been known to be a robust invader of ecosystems but presence in the Baltic is still not well explained. Four high spatial resolution models have been developed, three respective Round Goby and one for Mitten Crab. Two models are specific to the Blekinge/Hanöbukten region of the Swedish Baltic Sea coast, showing predicted current distribution of Round Goby. Two are predictions of Round Goby and Mitten Crab transferred or projected to other regions, with different approaches in setting model parameters and choosing variables, showing current and potential distribution. This study features: exploratory data analysis and filtering using GIS tools, highly discriminant environmental variable selection and rejection, and several different approaches to modelling in Maxent using custom and default settings. Predictive maps have been developed showing current distribution and potential spread as well as explanatory tabular data outlining direct and indirect drivers of species presence. Maxent has proven to be a powerful predictive tool on a regional basis, and proximity to introduction locations play a major role. Maxent, used in combination with spatial data modelling, exploration and filtering techniques has yielded a valid explanatory model as well. Transferring predictions to other regions is quite sensitive, however, and can depend heavily on species, sampling strategy and similarity of habitat type. Round Goby predictions were successfully created regionally and transferred to Stockholm, but Mitten Crab predictions were not successfully transferred to Blekinge.