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Quagga Mussel Induced Phosphorus Cycling Changes In Lake Michigan, Rae-Ann Maclellan-Hurd

Theses and Dissertations

Quagga mussels (Dreissena rostriformis bugensis) are an invasive ecosystem engineer that have successfully colonized both profundal and nearshore regions in Southern Lake Michigan. Quagga mussels directly altered the flow of nutrients by filtering particles, excretion of soluble forms of nutrients in the benthos, and through the production of biodeposits. Mussel excretion, egestion, and capture rates of P were compared between a 25 meter and a 55 meter deep site near Milwaukee Harbor to determine the retention of nutrients in these regions. The capture rate of particulate phosphorus at the 25m site (278 ± 388 μmol m-2) was similar to that …

An Investigation Into The Trophic Magnification Of Polychlorinated Biphenyls In The Lake Michigan Food Web, Philip Hurst

Theses and Dissertations

Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants known to contribute to several adverse health conditions in humans including cancers and a suite of liver diseases. While there exist 209 unique PCB congeners, the World Health Organization has identified 12 that pose the greatest health risk to humans due to these congeners’ functional similarity to dioxins, another notoriously toxic class of contaminants. Along with methylmercury, PCBs are the primary drivers behind fish consumption advisories in the Great Lakes. These guidelines are informed primarily by surveys of contaminants in freshwater biota. However, the proliferation of invasive species, such as …

Round Goby-Induced Changes In Young-Of-Year Yellow Perch Diet And Habitat Selection, Christopher John Houghton

Theses and Dissertations

A critical step in the recruitment of age-0 yellow perch (Perca flavescens) to the

adult population occurs during their transition to the demersal stage. If larval age-0

yellow perch survive recruitment bottlenecks imposed by alewife (Alosa

pseudoharengus) and dreissenid mussels, they transition to demersal feeding in late

August and early September. In Lake Michigan, demersal age-0 yellow perch seek

rock substrate where they begin feeding on benthic invertebrates in late summer.

That research preceded the invasion of the round goby (Neogobius melanostomus), a

species that can have negative impacts on benthic forage. The current study used

the spread of round …

Phosphorus Recycling By Profunda Quagga Mussels In Lake Michigan, Caroline Mosley

Theses and Dissertations

Quagga mussels (Dreissena rostiformis bugensis) act as ecosystem engineers in the southern basin of Lake Michigan, altering physical habitats and biogeochemical processes. Adapted to cold and oligotrophic conditions, profunda quagga mussels thrive on the soft substrate of deeper depths. At a 55 m site (10,000 mussels m-2) offshore from Milwaukee, WI, profunda mussel biomass (g m-2) was 1/3 of biomass (g m-2) measured at a 10 m comparison site (5,000 mussels m-2). Higher densities but less biomass is due to profunda mussels having less tissue for a given length and the population per m2 comprising of mostly small mussels ( …

Plankton Trophic Structure Within Lake Michigan As Revealed By Stable Carbon And Nitrogen Isotopes, Zachery G. Driscoll

Theses and Dissertations

Zooplankton represent a critical component of aquatic food webs in that they transfer energy from primary producers to higher trophic positions. However, their small size makes the application of traditional trophic ecology techniques difficult. Fortunately, novel techniques have been developed that can be used to elucidate feeding information between zooplankton species. I used the analysis of stable carbon and nitrogen isotope ratios to estimate the trophic structure of Lake Michigan's zooplankton community. The major zooplankton species, three size classes of seston, and seston from specific water column depths were collected in 2011 and 2012 for stable isotope analysis. Trophic position …

Lake Michigan Hydrodynamics: Mysis And Larval Fish Interactions, Yutta Wang

Theses and Dissertations

I studied the interactions between Lake Michigan hydrodynamics (the spring thermal bar) and Mysis, deepwater sculpin, and burbot larvae. The thermal bar is a zone of sinking 4º С water that separates warmer inshore water from colder offshore water. Mysis was a major bycatch of sampling for larval fishes. The density of Mysis did not differ statistically between inshore (about 6º С) and offshore of the thermal bar, but the percentage of Mysis that were newborns was significantly higher inshore (P = 0.007). These "early start" coastal Mysis may have an advantage in growth and survival, but with the risk …

Nearshore Benthic Oxygen Dynamics In Lake Michigan, Emily H. Tyner

Theses and Dissertations

The intense colonization of the Laurentian Great Lakes by dreissenid mussels has profoundly changed ecosystem processes, particularly benthic oxygen dynamics. Dissolved oxygen concentrations in mussel beds, sloughed Cladophora mats, and sediment indicate that hypoxia forms and disappears in some substrata (ephemeral Cladophora mats), while occurring consistently in others (depositional areas of sloughed Cladophora). Dissolved organic carbon concentrations are high (mean: 143 ± ± 28 ppm) in depositional Cladophora mats but lower (˂ 10 ppm) in most other environments. Field sampling and laboratory experiments suggest that under conditions of low water velocity and thick Cladophora cover, hypoxia may develop atop …

Changes In The Lake Michigan Trophic Structure: As Revealed By Stable C And N Isotopes, Benjamin Turschak

Theses and Dissertations

Food web structures which incorporate both slow (nearshore or detrital) and fast (pelagic) energy channels convey stability upon food web biota through asynchrony and multichannel trophic omnivory. Within the Lake Michigan food web, invasive dreissenid mussels have caused rapid changes to food web structure and energy flows. I used stable C and N isotopes and gut content analysis to determine how Lake Michigan food web structure and stability has changed in the past decade, coincident with the expansion of dreissenid mussels and a decrease in pelagic phytoplankton production. Fish and invertebrate samples collected near the port of Milwaukee, WI were …