Bythotrephes longimanus, a predacious zooplankter, has invaded >130 inland lakes in
North America, yet few studies have documented the long-term phenology and impact of
an invasion. This study used Bythotrephes spines and Daphnia ephippia in 210Pb-dated
sediment cores from four sites in Island Lake Reservoir (Minnesota, United States) to
document the establishment and growth of the Bythotrephes population and to examine
corresponding changes in daphnid species composition and density during a 40-year
period spanning the invasion. Based on sediment evidence, Bythotrephes invaded the
reservoir in 1982.2, or about 8 years prior to what was its first detection in the water
column in 1990. If accurate, this makes Island Lake Reservoir the first documented
inland lake invaded in North America. Year to year population density of Bythotrephes
followed a logistic growth model, and generally took about 10 years to reach annual
carrying capacity. A notable impact of Bythotrephes on the daphnid community occurred
within the first few years but did not intensify with increased Bythotrephes density over
time. Daphnid species composition shifted in the western basin toward D. mendotae
dominance, but did not shift in the eastern basin. The reservoir maintained a population
of its largest-bodied daphnid, D. pulex, despite Bythotrephes presence. Coincident with
Bythotrephes invasion, mean daphnid ephippium size decreased both within species and
for the whole 3-species daphnid assemblage. This research suggests that lakes could
harbor Bythotrephes for years before its first detection in the water column, that annual
population build-up of Bythotrephes may require years before reaching peak annual
densities, that the impact of Bythotrephes on food webs occurs relatively quickly, and
that long-term impacts of Bythotrephes in a reservoir may be less severe than in natural
University of Minnesota M.S. thesis. January 2012. Major: Integrated Biosciences. Advisor: Dr. Donn K. Branstrator. 1 computer file (PDF), v, 70 pages.
Beranek, Ashley Elizabeth.
An assessment of the long-term phenology and impact of Bythotrephes longimanus in Island Lake Reservoir, Minnesota, using sediment records..
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