Mercury concentration and aquatic food web alterations associated with zebra mussel invasion in Minnesota lakes
2023-08
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Mercury concentration and aquatic food web alterations associated with zebra mussel invasion in Minnesota lakes
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2023-08
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Abstract
Zebra mussels (Dreissena polymorpha) are an invasive species documented in 299Minnesota lakes, with 231 of those lakes managed as walleye fisheries. Many ecological changes
are associated with zebra mussel invasion, including increased water clarity, depleted pelagic
energy resources, expanded littoral zones, deposition of benthic organic matter causing anoxic
sediments, and increased benthic energy reliance of food webs. However, the effects of zebra
mussels vary among lakes, and few opportunities exist to examine lake ecosystems and food
webs pre- and post- zebra mussel invasion. Furthermore, recent evidence has suggested that
Dreissenid mussels may impact contaminant bioaccumulation in higher trophic levels, but these
effects have not been well-studied in inland lakes. I took two distinct approaches to
understanding zebra mussel impacts on food webs and contaminants in fishes. I combined
historic Minnesota statewide mercury monitoring data from 1997-2021 coupled with stable
isotope data to provide insight into food web dynamics and mercury concentration alterations
with zebra mussel invasion. I found the probability of exceeding the Minnesota safe threshold for
safe eating of average sized northern pike (Esox Lucius) and walleye (Sander vitreus) ranged
from 60%-70%, with zebra mussel lakes having an increased chance. Specifically, mercury
concentrations analyzed using Before-After Control-Impact (BACI) study design increased by
8.2% in northern pike and 15.4% in walleye for invaded lakes, while uninvaded systems were
stagnant or decreased. To quantify resource use and community structure, food webs in Leech
Lake were analyzed pre- and post- invasion using stable isotope analysis of δ13C and δ15N. Fish
community response to zebra mussel invasion varied spatially in Leech Lake. Bays on the
western shoreline of Leech Lake with heterogeneous habitat increased niche size by 39.81% and
fish in those areas relied more heavily on benthic resources following invasion. In contrast to the
western bays and to hypothesized effects of zebra mussels, fish from the main basin of Leech
Lake, containing mostly homogenous pelagic resources, decreased in niche size by 32.26% and
relied more heavily on offshore resources. Taken together, high mercury concentrations in
Minnesota northern pike and walleye are exacerbated in zebra mussel lakes. Food web dynamics
are variable within the same lake, suggesting preexisting food web structure and access to
benthic resources are important to community resilience with zebra mussel invasion.
Description
University of Minnesota M.S. thesis. August 2023. Major: Water Resources Science. Advisor: Gretchen Hansen. 1 computer file (PDF); v, 128 pages.
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Link, Denver. (2023). Mercury concentration and aquatic food web alterations associated with zebra mussel invasion in Minnesota lakes. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/259558.
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