Date of Award


Access Control

Open Access

Degree Name

Great Lakes Ecosystem Science


Great Lakes Center


Lyubov Burlakova

Department Home page

First Reader

Lyubov E. Burlakova

Second Reader

Allison R. Hrycik

Third Reader

Gavin M. Leighton


In the Laurentian Great Lakes, two invasive bivalves Dreissena polymorpha and Dreissena rostriformis bugensis have induced a number of changes, including increased water transparency, alterations in nutrient cycling, decreased chlorophyll concentrations, and changes in phytoplankton community composition and structure. These changes are likely to have implications for the deep chlorophyll layer (DCL), a feature characterized by phototrophic organisms reaching abundance at light levels far below ideal for photosynthesis. Though the impacts of D. polymorpha and D. r. bugensis in the Great Lakes have been studied for at least the last three decades, little is known about how these ecosystem engineers affect the features of the DCL, such as the depth at which it forms, the magnitude of space it occupies, and the concentration of chlorophyll it contains. I set out to explore the impacts of dreissenid biomass on these deep chlorophyll layer features and the relationships between dreissenid presence and variables that may impact or be impacted by their presence or by the presence of the deep chlorophyll layer, including water transparency, specific conductance, dissolved oxygen concentrations, photosynthetically active radiation, and chlorophyll-a fluorescence. I found that in some cases, increased dreissenid biomass was associated with decreased concentrations of total integrated chlorophyll in the deep chlorophyll layer, but no significant relationships between dreissenids and deep chlorophyll layer depth or thickness were observed. Consistently, water transparency was higher in the presence of dreissenids; significant relationships between dreissenid presence and specific conductance and dissolved oxygen concentrations were inconsistent but when they occurred, dreissenid presence was associated with greater dissolved oxygen concentrations and specific conductance, and lower chlorophyll fluorescence. DCLs can contribute significantly to overall primary productivity; understanding the impact of dreissenids on the deep chlorophyll layer—a feature which occurs commonly in most Great Lakes during summer stratification--is likely to increase in importance as the lakes shift towards increasing oligotrophy.