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The Summer (May through August) community of crustacean zooplankton and zebra mussel (Dreissena polvmorpha) larvae at a 15 m sample site in Lake Michigan near Michigan City was evaluated for the years 1990 through 1994. Yearly mean densities were compared with investigations done at the same sample location by Johnson (1972) and Ball State University (unpublished data) during 1970 and 1971, respectively to investigate possible changes in community composition during the past 25 years. Potential declines in crustacean zooplankton relating to the 1991 introduction of the filter-feeding zebra mussel were also evaluated.Overall declines in major species since 1970-71 included Bosmina longirostris, Daphnia retrocurva, and Diacyclops thomasi. Recent increases in the nearshore fish population of alewife (Alosa pseudoharengus) and spottail shiner (Notropis hudsonius) may have influenced the densities of these species in recent years. Copepod nauplii were the only crustaceans to increase in overall abundance since the period of 1970-71, as the number of invertebrate predators appeared to decrease. Other species did not show any noticeable change in long-term abundance or during the 1990-94 period.Zebra mussel larvae were first observed in the zooplankton complex studied on June 17, 1991. -Densities of larvae reached maximal levels for the period of study in 1994 with two large reproductive pulses of 195,000 and 210,000/m3 in June and August, respectively. The mean abundance during 1994 made up 65% of the total crustacean zooplankton/zebra mussel community complex. Evaluation of the vertical stratification of zebra mussel larvae in 1994 revealed a strong (r2=0.75, p<0.0005) tendency for veligers to remain in the upper 10 m of the water column due to thermal stratification. / Department of Biology

Biological invasions threaten the stability and biodiversity of freshwater ecosystems worldwide. The impacts of an invading species often vary across systems, making their prediction difficult. When data from multiple invaded sites are available, statistical models can be developed to correlate an invader's distribution and abundance with local environmental variables; such models could then provide managers with useful tools to help prioritize efforts to control the invader. The introduction of the zebra mussel (Dreissena polymorpha) and quagga mussel (D. bugensis) to North America ranks among the most ecologically and economically disruptive aquatic invasions ever documented. While some attempts have been made to predict zebra mussel occurrence and abundance, none have been made for quagga mussels. Furthermore, few studies have been based on river systems, which possess the bulk of North American freshwater biodiversity. I related zebra and quagga mussel occurrence and biomass to physical habitat variables (calcium concentration, substrate size and depth) in the St. Lawrence River. I then developed predictive models of abundance for each species from combinations of these variables. Each variable explained a significant amount of variation in mussel biomass, but different combinations of variables were obtained for each species. Although these models do not account for all of the variation in abundance, they do provide a useful basis for predicting dreissenid distribution and abundance in other invaded river systems.

Biological invasions are a global phenomenon that can threaten native species and disrupt ecosystem processes. Exotic species also impact ecosystems in less conspicuous ways by provoking native species to alter their foraging behaviour. Subtle impacts such as diet shifts are frequent, and can have consequences for food web dynamics and the fitness of native predators. Diet shifts involving the consumption of exotic species require native predators to recognize, capture and handle novel prey. In this thesis, I document a diet shift in the St. Lawrence River involving a common native fish and Eurasian mussels that invaded the river in the early 1990s. I conducted diet analysis of yellow perch (Perca flavescens) at multiple sites in the upper St. Lawrence River and discovered that they consumed substantial quantities of zebra and quagga mussels (Dreissena spp.) in the Soulanges Canal, an artificial waterway west of Montreal. This was unexpected because perch lack adaptations for crushing molluscs. This foraging innovation was not observed at the same site in the early 1990s or at other sites at any time. Mussel shells were weaker at this site, probably because of exposure to calcium-poor water. This suggests that water chemistry mediates yellow perch predation on mussels. This study provides an example of diet shifts involving exotic prey and illustrates the influence of abiotic factors on species interactions.

Eutrophication is a consequence of excess nutrients in the water which leads to increased algaegrowth, reduced water transparency and hypoxic bottoms. This is the biggest environmental problemfor the Baltic Sea which recently has resulted in stricter legislations and other initiatives to help theBaltic Sea to recover. However, the actions to reduce the nutrient input to the Baltic Sea have so farmainly been land-based. These actions seem to not be enough since the eutrophication continues tobe a problem for the Baltic Sea. Farming blue mussels has shown to have a mitigating effect on theeutrophication and could thus be a complementary action. Blue mussels are filter-feeding specieswhich means that they filter water for food and thus eat phytoplankton and accumulate nutrients atthe same time. When the blue mussels are removed from the sea, so is the nutrients accumulated inthe mussels, resulting in a mitigation of nutrients and thereby the eutrophication. Due to the brackishwater with the low salinity in the Baltic Sea, the blue mussels farmed there do not grow bigger thanaround 3 cm. This means that the mussels are not suitable for human food production and theharvested mussels need to be used for something else, even though the farming itself is anenvironmental action. Three possible mussel products from valorisation of the Baltic Sea blue musselshave been identified; producing mussel meal, biogas or compost.Region Östergötland is involved in a project, Baltic Blue Growth, with the main objective to study howto use mussel farming as an environmental measure and which of the three valorisation options is themost beneficial from an environmental perspective. This study is a part of their investigation to reachtheir goal and will study their mussel farm in St. Anna and the three valorisation options from anenvironmental perspective. The aim of this study is thus to investigate the net nutrient reduction froma mussel farm in the Baltic Sea in combination with the contribution to climate change. This is donefrom a life cycle perspective to include the valorisation of the mussels into the different productsmussel meal, biogas or compost. For this, an existing farm in the archipelago of St. Anna, Östergötland,Sweden is studied. The main results show that there is a nutrient reduction from the mussel farm andthis is not majorly affected regardless of which valorisation option that is chosen. However, the musselfarm does have an impact on climate change and the magnitude of the impact varies for the threevalorisation options. The results of the sensitivity analysis show that the result from the life cycle canbe improved with future improvements of the mussel farm and transportation. The nutrient reductioncan become larger and the impact on the climate change can be reduced. Outside the result from thelife cycle analysis it is discussed that there are other future improvement possibilities in the productionof the mussel products, which would impact the result. The mussel farm and the mussel products alsohave other positive impacts that is not included in the life cycle analysis but discussed in the study,such as increased water transparency, recycling of nutrients and reduction of over fishing. However,the mussel farm could also have negative impacts, such as emissions of microplastics and locallyincreased sedimentation which affect the hypoxia. Those are discussed in this study but the probabilityand possible impact of them are not fully investigated and need further research.

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Freshwater mussels are particularly susceptible to injury from exposure to hazardous substances due to their sessile nature and filter feeding biology. There have been various Natural Resource Damage Assessment and Restoration (NRDAR) cases in the United States involving injury to freshwater mussels due to releases of hazardous substances into rivers and streams. Restoration of mussels in these cases typically involves propagation of mussels at a hatchery facility and their subsequent stocking or release at restoration sites. However, determination of the services lost due to injury to mussel populations and the appropriate level of restoration (and associated costs) to recover those losses has varied among NRDAR cases. Standardized methods would facilitate injury determination and restoration planning for future cases involving injury to mussels. The purpose of this research was to use two of the earliest and largest NRDAR cases (Certus, Inc. and Lone Mountain Processing, Inc. (LMPI)) involving injury to mussels to: 1) determine whether restoration for these cases was sufficient and 2) analyze restoration efforts for application in future NRDAR cases (i.e., lessons learned and development of standardized methods). This study represents the first evaluation of mussel restoration efforts in a NRDAR context. In general, 4.8% to 6.1% of juvenile mussels that excysted from host fishes in the hatchery survived to be eventually released at restoration sites. Further, based on expected survival and recruitment rates of released mussels, monitoring of restoration sites found 43% to 15% of the expected number of mussels. Understanding reasons for this discrepancy between expected and estimated survival is critical for determining the level of restoration success. If released mussels are either establishing and/or recruiting outside of monitoring area but otherwise alive and breeding, then they should count towards successful restoration. In contrast, if released mussels have either high mortality over time or are dying shortly after release, then expected gains from these mussels should not count towards successful restoration. I developed a mussel-specific Resource Equivalency Analysis (REA) for use in future NRDAR cases that compares the loss of services, using Discounted Mussel Years (DMYs) as units, to the expected gain in services from restoration. Applying this analysis to the Certus and LMPI NRDAR cases suggests that mussel restoration was successful (i.e., expected DMYs gained are greater than those lost), even when it was assumed that 75% of released mussels were dying after being released at restoration sites. Finally, a cost analysis of two mussel propagation facilities found that the yearly cost per mussel released at a restoration site ranged from $4.36 to $96.48. The suite of species propagated each year varied. As some species are more difficult to propagate than others, the cost per mussel varied widely. These data will facilitate the determination of restoration costs in future cases. Together, this information provides a starting point for consistently estimating restoration effort and costs for future NRDAR cases involving freshwater mussels. / Doctor of Philosophy / Freshwater mussels provide numerous ecosystem services. Most importantly, they purify large volumes of water, and provide habitat and food for other animals. However, they are highly vulnerable to chemical spills because they cannot move long distances quickly and they are directly exposed to toxic substances if they filter water. There have been many cases in past decades where vulnerable mussel populations were exposed to chemical spills. When these populations are injured, the services they provide are lost until the population can be restored to pre-spill conditions. Restoration of mussel populations usually involves raising juvenile mussels in hatchery facilities and then releasing them in areas where populations were injured. Determining the appropriate level of restoration needed to restore populations has varied widely among cases. A standardized approach would facilitate determination of restoration and restoration costs. I used data from two cases (Certus, Inc. and Lone Mountain Processing, Inc.) where mussel populations were injured due to a chemical spill to: 1) determine whether restoration for these two cases was successful and 2) develop tools and draw insights for use in future cases where mussels are injured. This study represents the first evaluation of restoration success of freshwater mussels in a NRDAR context. On average, 4.8% to 6.1% of juvenile mussels produced at two Virginia hatchery facilities survived to be released at restoration sites. Further, of the mussels released, only 43% to 15% of the expected mussels were found in later years. These "missing" mussels are either leaving and/or breeding outside of their release areas, or they are dying and failing to provide important ecosystem services. Further study is needed to determine the degree to which each of these is the case. I also developed a mussel-specific method of determining how much restoration is needed to provide the amount of ecosystem services as pre-spill conditions (called Resource Equivalency Analysis or REA). Application of REA to these two test cases (Certus, Inc. and Lone Mountain Processing, Inc.), I showed that restoration for these cases was successful, even if as much as 75% of released mussels are dying after being released at restoration sites. Finally, I found that the cost of successfully releasing a mussel ranged from $4.36 to $96.48 per mussel. This information is useful for estimating the cost of restoration plans in future chemical spills that injure freshwater mussels.

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Biological invasions are among the leading causes of species diversity loss; however, the impacts of invasion are context-dependent and can vary with the local environment. The mechanisms governing variation in impact and their relationship to specific abiotic and biotic factors remain largely unexplored. Recent local declines in native unionid mussels have been attributed to the invasion of North American lakes and rivers by the Eurasian zebra mussel ( Dreissena polymorpha), as a result of intense fouling of unionid shells by zebra mussels. My research investigated the role of abiotic and biotic factors in mediating the impact of zebra mussels on native mussels. I examined the impact of zebra mussels on unionids in a habitat thought to be suboptimal for zebra mussels and compared this to the impact observed in other invaded habitats. A predictive model relating fouling intensity to local environmental variables (calcium concentration, sediment particle size) was developed, and a predator-exclusion experiment was conducted to investigate the role of predation in mediating fouling intensity. Overall, I found that two abiotic factors of the local environment were significant predictors of fouling intensity and that relationships used to predict the impact of zebra mussels could be extended to a broader range of habitats.