Final Report: Complex Interactions Between Harmful Phytoplankton and Grazers: Variation in Zebra Mussel Effects Across Nutrient Gradients

EPA Grant Number: R831708
Title: Complex Interactions Between Harmful Phytoplankton and Grazers: Variation in Zebra Mussel Effects Across Nutrient Gradients
Investigators: Sarnelle, Orlando , Hamilton, Stephen , Peacor, Scott , Rose, Joan B. , Vanderploeg, Henry
Institution: Michigan State University , NOAA / GLERL
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 2006 through December 31, 2007 (Extended to December 31, 2008)
Project Amount: $454,779
RFA: Ecology and Oceanography of Harmful Algal Blooms (2004) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Ecosystems , Water


  1. Experimentally determine whether the effect of Dreissena on M. aeruginosa changes direction across a gradient of phosphorus loading
  2. Identify thresholds in P loading at which the Dreissena effect changes direction
  3. Understand the mechanisms underlying the complex interaction between Dreissena and M. aeruginosa, with the explicit goal of predicting the consequences of changes in nutrient loading on harmful phytoplankton abundance in invaded habitats
  4. Determine the degree to which experimental results from inland lakes are relevant to the interaction between Dreissena and M. aeruginosa in the western basin of Lake Erie
  5. Determine the extent to which Dreissena promotion of M. aeruginosa translates into increased levels of cyanobacterial toxin levels in the Great Lakes

Summary/Accomplishments (Outputs/Outcomes):

We have experimental evidence that an increase in phosphorus loading can reverse the effect of zebra mussels on the abundance of the toxic cyanobacterium, Microcystis aeruginosa. Specifically, the 2008 results provide experimental support for the hypothesis that the striking contrast in mussel influence on M. aeruginosa documented across habitats (Smith et al. 1998, Vanderploeg et al. 2001, Nicholls et al. 2002, Raikow et al. 2004) may be at least partly a consequence of differences in ambient nutrient levels in those habitats. At low P levels, the effect of mussels was significantly positive, whereas at the highest P level the effect was significantly negative. One possible explanation for these results is a change in mussel feeding selectivity across P levels, in response to changes in the per capita production of the peptide toxin, microcystin, by M. aeruginosa. Increased P loading decreased the microcystin quota of M. aeruginosa in the field, possibly as a result of N limitation of peptide synthesis, and mussel grazing rates were negatively related to microcystin concentrations. Given the importance of microcystin as a public health issue, furthering our understanding of how environmental factors such as N and P loading seems critical. Such understanding is also important from a management perspective given that N and P loading are strongly driven by human activities. Phosphorus addition alleviates P limitation in M. aeruginosa, based on our results from the western basin of Lake Erie, which may have reduced the stimulating effect of P excreted by mussels in the enclosure experiments. Monitoring data from Lake Erie also showed that total phosphorus was an inconsistent predictor of microcystin concentrations, which is congruent with the variable effects of nutrient enrichment on M. aeruginosa in the our field experiments. Sometimes adding P decreased or reversed the positive influence of mussels on M. aeruginosa.

It is also possible that there is large spatial variability in dreissenid grazing in the western basin given that there is large variation in turbidity and substrate type. In the laboratory, we have found that 1) multiple genotypes of M. aeruginosa coexist in lakes and that these genotypes may vary considerably in growth rate and palatability to mussels. We have also developed a method for measuring the growth rate of individual phytoplankton colonies that has enabled the first demonstration of the growth-rate cost of increased colony size. These mechanistic results will be critical for parameterizing models that can predict the complex effects of grazers on harmful algal blooms in freshwater ecosystems.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other project views: All 9 publications 3 publications in selected types All 3 journal articles
Type Citation Project Document Sources
Journal Article Hamilton SK, Bruesewitz DA, Horst GP, Weed DB, Sarnelle O. Biogenic calcite-phosphorus precipitation as a negative feedback to lake eutrophication. Canadian Journal of Fisheries and Aquatic Sciences 2009;66(2):343-350. R831708 (Final)
  • Abstract: NRC Research Press
  • Journal Article Knoll LB, Sarnelle O, Hamilton SK, Kissman CEH, Wilson AE, Rose JB, Morgan MR. Invasive zebra mussels (Dreissena polymorpha) increase cyanobacterial toxin concentrations in low-nutrient lakes. Canadian Journal of Fisheries and Aquatic Sciences 2008;65(3):448-455. R831708 (2007)
    R831708 (Final)
  • Full-text: Wilson Lab Full-text PDF
  • Abstract: NRC Research Press
  • Supplemental Keywords:

    RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Oceanography, algal blooms, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, marine ecosystem, bloom dynamics, nutrient kinetics, phytoplankton, human health, zebra mussels, grazing and window opportunities

    Relevant Websites: Exit

    Progress and Final Reports:

    Original Abstract
  • 2006
  • 2007 Progress Report