Starry stonewort (Nitellopsis obtusa) (Desvaux in Loiseleur) J. Groves is an invasive macro alga that can take over entire water columns and outcompete native species. Previous research has quantified seasonal life history and phenology but there is no research quantifying carbohydrate allocation which was the aim for Chapter II. Management efforts to control Nitellopsis obtusa have been limited to stressing the thalli and have not been able to directly target the reproductive bulbils on larger scales. Smaller scale efforts such as the use of hand pulling can be used but hand pulling is not realistic for larger infestations. Chapter III was conducted to test the effects of clipping and harvesting stress on N. obtusa to give a baseline on the effect of stress on the production of bulbils and the regrowth of thalli. Management needs to stress the growth of N. obtusa as much as possible to reduce the production of bulbils and limit the spread of current infestations in waterways. Both studies utilized samples harvested from Lake Koronis, Minnesota, USA from 2020 and 2021 to quantify starch allocation patterns in N. obtusa and to grow reserve cultures of N. obtusa. Starch was quantified using the Amylase/Amyloglucosidase method through a commercially purchased STA20 starch assay kit from Sigma Aldrich (Sigma Aldrich, St. Louis, Missouri). The starch data was then compared to environmental variables such as light transmittance (%), pH, and water temperature (℃) via mixed procedures models in SAS. The seasonal average low and high points of starch storage were observed to be June (3.3%) and April (24.9%) for thalli biomass then June (21.0%) and November (73.0%) for bulbils. These bulbils spread easily, spread rapidly, can store a lot of energy (73% starch), and are a major concern for the invasion of N. obtusa. Thalli biomass (g) was about 97.0% lower than reference thalli biomass after four clipping treatments and bulbil density (N m-2) was about 46.0% lower than reference bulbil density after one clipping treatment. Suggesting that mechanical clipping stress opens the water column to induce bulbil sprouting and reduce the total bulbil bank in the sediment. Mechanical clipping treatments would then be recommended to be used in conjuncture with other management methods to stress the alga as much as possible to reduce total biomass and bulbil production starting in June.


Ryan Wersal

Committee Member

Matthew Kaproth

Committee Member

Gray Turnage

Date of Degree




Document Type



Master of Science (MS)

Degree Program/Certificate



Biological Sciences


Science, Engineering and Technology



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