Browsing by Subject "Zooplankton"

Now showing 1 - 7 of 7
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    Acoustic Observations of Zooplankton Migration in Lake Superior
    (2023-07) Murr, Ashley
    The diel vertical migration (DVM) of aquatic organisms in marine environments is commonly studied using acoustic instruments because of their ability to sample with high spatial and temporal resolution for extended periods of time. The practice of using acoustic instruments in the Laurentian Great Lakes, however, is not as widespread. This research presents six years of Acoustic Doppler Current Profiler (ADCP) backscatter data from a site in Lake Superior to demonstrate that ADCPs can increase the resolution and robustness of data pertaining to the vertical migration of freshwater organisms, presumably zooplankton. We observed migratory behavior with sub-hour sampling over the course of entire seasons, including transitional seasons and the winter. The data distinctly reveals a diurnal signal consistent with DVM. In addition, with the high resolution of the data, we observe lunar and seasonal variation in the diurnal signal. We employ a simplified method using the change in measured intensity to isolate the diurnal signal, allowing us to compare data regardless of instrument modification, backscatter calibration, and range correction. We do not estimate abundance, biomass, population distribution, or species identification, instead we offer general observations on DVM patterns over days, months, and years to supplement standard biological sampling methods.
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    The effects of physical variables on zooplankton distributions in stratified lakes.
    (2007-10) Spitael, Maria Susan
    Zooplankton play a vital role in lake ecosystems. They serve as an important food source for fish, as well as being major consumers of algae, which contributes to greater water clarity. To understand the dynamics in a lake, it is necessary to understand zooplankton and how they are affected by the physical environment around them. The purpose of this research was to address the question of how turbulence and temperature stratification affect zooplankton aggregations in lakes. Laboratory experiments were performed to quantify the effects of temperature and turbulence on zooplankton distributions in a stratified tank. These measurements were designed to measure zooplankton aggregations and to provide detailed information on the physical conditions causing them. Comprehensive field measurements were taken throughout one summer, covering five 24-hour periods, in order to investigate the effects of temperature and turbulence on zooplankton aggregations in the field. A high-frequency sonar measurement device was developed to take the measurements by modifying the output of a commercial fish-finder and calibrating it to match zooplankton net counts. Our results showed that zooplankton distributions are strongly affected by temperature and turbulence, and that these effects are species-specific, and are different between day and night.
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    Evaluation of the potential effects of methoprene and BTI (Bacillus thurinqiensis israelensis) on wetland birds and invertebrates in Wright County, MN, 1988 to 1993
    (University of Minnesota Duluth, 1995) Niemi, Gerald J; Axler, Richard P; Hanowski, JoAnn M; Hershey, Anne E; Lima, Ann R; Regal, Ronald R; Shannon, Lyle J
    This report summarizes the results of a six year study (1988 to 1993) to assess the potential effects of two mosquito control materials, methoprene (applied as Altosid sand granules) and Bacillus thuringiensis var. israelensis (Bti, applied as Vectobac-G granules) on zooplankton, aquatic insects, and breeding birds in the Twin Cities metropolitan area. The study was a before-and-after design with 1988 to 1990 as pre-treatment and 1991 to 1993 as treatment years. A total of 27 wetlands in western Wright County were randomly selected and randomly placed within one of three groups of sites: 9 control, 9 Bti-treated, and 9 methoprene-treated. Selected populations of zooplankton, aquatic insects, and breeding birds were sampled within each of these wetlands. Each site was also monitored to verify the applications of Bti or methoprene to the respective sites and to verify that the control sites were not treated. In 1992, the number of study sites was reduced to 26 because of the loss of one methoprene-treated site from sampling. No effects could be attributed to treatment on zooplankton or breeding birds. Aquatic insects, however, were considerably reduced following treatments in 1992 and 1993. Chironomids comprised approximately 60% of the total individuals sampled, and were greatly reduced in both methoprene and Bti sites compared to controls. We focused on this group particularly because of their abundance, but also because they are closely related to mosquitoes and known to be susceptible to both larvicides. However, our results showed that all insect groups were similarly affected by both larvicides. Both Bti and methoprene applications to these wetlands reduced aquatic insect densities by a range of 57-83% and biomass by a range of 50-83% in the second and third years of treatment. Following the effects of treatments observed in 1992, populations of aquatic insects recovered to pre-treatment levels at the start of 1993, but quickly declined again following treatment. No food chain effects of these declines, with the possible exception of increases in the density of some copepods in methoprene-treated sites, were observed in either zooplankton or in breeding birds. High nest loss rates due to predation may have been a greater limiting factor to birds than mosquito control treatment. The carrying capacity of bird populations may also be lower than that affected by food reductions, especially since alternative foods tended to be available for Red-winged Blackbirds outside of the wetland study sites. Even though this study represents one of the largest ever conducted to assess the effects of mosquito control materials on non-target organisms, a variety of questions regarding the overall effects of mosquito control treatments remain unanswered. Among the most pressing questions are the determination of the long term effects (e.g., > 5-10 yrs) of the control program and whether populations of aquatic insects can continue to recover within these treated areas.
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    Hypoxia tolerance of the invasive zooplankton Bythotrephes longimanus and the native zooplankton Leptodora kindtii
    (2015-12) Sorensen, Michael
    A predatory species of Eurasian zooplankton, Bythotrephes longimanus (spiny water flea), has been invading lakes and damaging food webs across the central part of North America since the early 1980s. In an effort to understand its niche, I investigated its short term survival under low dissolved oxygen (D.O.) concentrations in the laboratory and compared it to the native predatory zooplankton Leptodora kindtii. Both species are large-bodied, strongly selected by zooplanktivorous fish, and known to commonly engage in diel vertical migration. Trial conditions were chosen to mimic the hypolimnion of a eutrophic temperate zone lake during late summer. Tested B. longimanus (n=690) exhibited a pooled hypoxia tolerance limit (LC50) of 1.65 mg/L D.O. (95% confidence interval: 1.59, 1.72), while that of L. kindtii (n=380) was 0.58 mg/L D.O. (0.51, 0.65). Both species were more tolerant of hypoxia than zooplanktivorous fish, which cannot generally withstand prolonged exposure to D.O. concentrations lower than 2 mg/L. However, B. longimanus was significantly less tolerant than L. kindtii, and may exhibit greater spatial overlap with zooplanktivorous fish in seasonally-hypoxic lakes. These lab-based physiological results are consistent with landscape-scale observations that B. longimanus successfully invades primarily mesotrophic and oligotrophic lakes while L. kindtii thrives across a wider range of lakes, including eutrophic ones. The combined effects of climate change and cultural eutrophication throughout the 21st Century will likely increase the occurrence of temperate lake hypoxia, and provide a barrier to B. longimanus invasion of North American lakes.
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    Report of the Land-Based Freshwater Testing by the Great Ships Initiative of the Siemens SiCURE(TM) Ballast Water Management System for Type Approval According to Regulation D-2 and the Relevant IMO Guidelines
    (University of Minnesota Duluth, 2010) Cangelosi, Allegra
    The Great Ships Initiative (GSI) provides independent no-cost performance verification testing services to developers of ballast treatment systems and processes at a purpose-built, land-based ballast treatment test facility located in the Duluth-Superior Harbor of Lake Superior. GSI test protocols are consistent with the requirements of the International Convention for the Control and Management of Ships Ballast Water and Sediments (International Maritime Organization, 2004). GSI procedures, methods materials and findings are publicly accessible on the GSI website (www.greatshipsinitiave.org). In August through October 2009, the GSI conducted land-based tests on the SiCURETM Ballast Water Management System in cooperation with German Bundesamt für Seeschifffahrt und Hydrographie (BSH), i.e., the German Federal Maritime and Hydrographic Agency. During the series of five consecutive valid trials, the SiCURETM Ballast Water Management System was evaluated for its ability to: (a) successfully treat ballast water without interruption, (b) meet IMO D-2 discharge standards after a five-day holding time, and (c) discharge water after the five day retention period that is environmentally benign (i.e., no residual toxicity) pursuant to United States Environmental Protection Agency water quality criteria. It should be noted that because freshwater zooplankton are in general smaller than their salt and brackish water counterparts, the larger regulated size category (greater than 50 μm in minimum dimension) did not incorporate all live zooplankton that were present in the source water assemblage. The Siemens SiCURETM Ballast Water Management System functioned properly during the five consecutive trials, and was highly effective at reducing live organism densities in the fresh water ambient conditions of Duluth-Superior Harbor, as amended in these tests to achieve IMOconsistent challenge conditions. Live organisms in the regulated size classes were discharged in densities below the IMO D-2 standard. Microbial analyses showed system performance in keeping with IMO requirements for bacteria. Chemistry data generated across trials indicated the post-retention discharge to have well less than 0.1 mg/L total residual chlorine (TRC) under ambient conditions. Ambient water collected immediately after treatment and held in a cold environment had TRC and total residual oxidant (TRO) levels which slightly exceeded this level. However, in a real world application, the intake water would also be cold, and developers claim that the test system is designed to respond to this circumstance (reflected in oxidation-reduction potential, or ORP) with a reduction in chlorine generated and injected into the intake stream. There were no acute toxic effects of treated discharge on any test species across assays and trials. Chronic toxicity effects in 100 % effluent were detected in one out of two trials for test species of zooplankton and phytoplankton. There were no chronic toxicity effects across organisms and trials in 50 % or lower effluent dilutions.
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    Spatial and temporal variability in zooplankton-fish interactions in freshwater communities.
    (2011-06) Holbrook, Beth Victoria
    Abiotic and biotic factors interact at multiple scales to create heterogeneity in the distribution of zooplankton and zooplanktivorous fish in the pelagic area of freshwater lakes. In this dissertation, I explored the predator-prey relationship between these trophic levels in four studies conducted at a variety of spatial and temporal scales. The objective was to identify the processes that may structure spatial heterogeneity in these populations. At the smallest scales in the laboratory, I simulated light and temperature conditions similar to those found in an oligotrophic lake and observed interactions between age-0 lake trout (Salvelinus namaycush) and mysids (Mysis diluviana), and determined that the intake rate of age-0 lake trout (mg min-1) could be modeled as a function of mysid biomass (mg m-2). I then applied this model to field data collected at intermediate scales at a spawning shoal in Lake Superior and determined that age-0 lake trout distributed in a spatially predictable pattern based on maximizing their growth rate potential. I also explored the more general relationship between pelagic zooplankton biomass and fish density at intermediate spatial scales in three north temperate lakes. In all six depth strata that I analyzed, there was consistent and significant autocorrelation in the distribution of zooplankton biomass, but spatial structure in the distribution of fish density was weaker and more variable. I also detected a significant bottom-up influence of zooplankton biomass on the spatial structure of fish density in three of the six depth strata that I analyzed, but I did not detect any top-down influences of fish density on the spatial structure of zooplankton biomass. Finally, I explored the influence of surface temperature and mesoscale eddies on the distribution of epilimnetic zooplankton biomass and fish density at large scales in Lake Superior. Circulation patterns associated with prevailing wind conditions could explain some of the spatial patterns in zooplankton biomass, but epilimnetic fish distributions showed no pattern during both years of the study.
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    Winter and summer zooplankton community and environmental parameters data of thirteen lakes located in Minnesota and Wisconsin
    (2021-05-26) Shchapov, Kirill; Ozersky, Ted; Wilburn, Paul; shcha001@d.umn.edu; Shchapov, Kirill; University of Minnesota Duluth Large Lakes Observatory
    This data set contains the results of a study on taxonomic and functional differences between winter and summer zooplankton communities in lakes across a trophic gradient. Thirteen lakes ('Sites.csv') were sampled across a large trophic status gradient for zooplankton abundance, taxonomic and functional community composition, and Carbon/Nitrogen (C/N) stable isotopes in relation to environmental parameters. Zooplankton abundance and taxonomic identification were made for all stations ('Zooplankton_abundance.csv'); nutrients and C/N stable isotopes values in file 'Environmental_parameters'; lakes light conditions in summer and winter are presented in file 'Light.csv'; bulk zooplankton C/N stable isotopes are in 'Zooplankton_sia.csv' file.