Abstract
Starry stonewort (Nitellopsis obtusa) is an invasive macroalga from Eurasia. Currently, starry stonewort’s invasive range consists of the upper Midwest and Great Lakes region, including the Mississippi River. Starry stonewort poses recreational and ecological problems by forming dense canopies that extend through the water column. Starry stonewort occupies a late-season niche space with dense biomass occurring in late July and persisting well into autumn. There is a lack of information on the ecophysiology of starry stonewort. In this study, two populations of starry stonewort, Minnesota and New York, were analyzed to compare regional differences in ecophysiology, along with chara (native species) serving as a control due to its widespread presence throughout the United States. Chlorophyll fluorescence was used on all three populations to determine photosynthetic efficiency at temperatures between 4-45°C. The ratio of variable to maximal fluorescence(Fv/Fm) measurements showed that the three populations have a high potential to be efficient at temperatures from 4-30°C, with values averaged at 0.713 and 0.670 for the starry stonewort population and chara respectively. The light-adapted quantum yield of photosystem II (ФPSII) measurements indicated similar patterns across the macroalgae populations, except at 30 and 35°C, where starry stonewort exhibited 28.7% higher values compared to chara. Gas exchange measurements were preformed using an infrared gas analyzer with an aquatic chamber at three temperature optimums (4°C, 27°C, 37°C). Results indicated the optimal temperature for photosynthesis for starry stonewort and chara were 27°C and 25°C, respectively. Net photosynthesis at 27°C was 0.0066 μmol g−1 s−1 for the two starry stonewort populations, which was 1.4 times higher compared to chara. These data suggest that starry stonewort has the potential to expand its range into warmer climates and could outcompete chara in warmer areas.
Advisor
Ryan Wersal
Committee Member
Christopher Ruhland
Committee Member
Michael Greer
Date of Degree
2026
Language
english
Document Type
Thesis
Degree
Master of Science (MS)
Program of Study
Biology
Department
Biological Sciences
College
Science, Engineering and Technology
Recommended Citation
Zellmer, T. J. (2026). A comparative analysis of the ecophysiology between the invasive macroalgae Starry Stonewort and the native macroalgae Chara to predict invasion potential [Master’s thesis, Minnesota State University, Mankato]. Cornerstone: A Collection of Scholarly and Creative Works for Minnesota State University, Mankato. https://cornerstone.lib.mnsu.edu/etds/1636/
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