Date of Award

Fall 12-2020

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)


Ecology and Environmental Sciences


Hamish Greig

Second Committee Member

Steve Coghlan

Third Committee Member

Mike Kinnison

Additional Committee Members

Jasmine Saros

Joseph Zydlewski


New England’s climate is changing faster than that of any other region in the continental United States. Over the last century, Maine has experienced an increase in annual temperature of approximately 1.48oC along with a 15 percent increase in annual precipitation. Temperature and precipitation play vital roles in shaping the ecology of freshwater environments. Therefore, changes in regional climate could undermine the structure and stability of Maine’s freshwater systems as they currently exist.

Maine currently harbors the last wild populations of Atlantic salmon (Salmo salar) in the United States. Atlantic salmon were once abundant in Maine streams, but suffered dramatic declines due to several factors including deforestation, overfishing, and the construction of dams. In 2000, Atlantic salmon were listed as a Federally Endangered species. As juveniles, salmon spend 1 to 3 years in Maine streams before smolting. However, salmon face several threats as juveniles in Maine streams, including changes in climate as well as competition from introduced or invasive species which could outcompete salmon for resources.

This dissertation examines these impacts on juvenile Atlantic salmon (Salmo salar) and the stream food webs in which they are embedded by (1.) Using temperature-controlled microcosm experiments to investigate the potential for climate-driven warming to exacerbate the effects of competition between native and invasive species from different thermal guilds. The results suggest that non-native smallmouth bass (Micropterus dolomeiu) have the potential to outcompete Atlantic salmon as waters continue to warm. (2.) Running dynamic regression models to analyze the relationship between juvenile Atlantic salmon condition, temperature, and precipitation for 9 streams across 4 drainages over a 16-year period. The results suggest that the impacts of climate change on salmon growth may vary by stream and spatial scale. (3.) Conducting an instream mesocosm experiment to investigate the food-web implications of interactions between omnivorous crayfish and predatory Atlantic Salmon. These results suggest that strong bottom-up processes occur when crayfish are present, whereby increased algal growth could promote the availability of macroinvertebrates important to salmon diet.