2007 Progress 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 Period Covered by this Report: January 1, 2006 through December 31,2007
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 Dreissna on Microcystis aeruginosa changes direction across a broad gradient of phosphorus loading;
  2. Identify thresholds in P loading at which the Dreissna effect changes direction;
  3. Understand the mechanisms underlying the complex interaction between Dreissna 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 Dreissna and M. aeruginosa in the western basin of Lake Erie
  5. Determine the extent to which Dreissna promotion of M. aeruginosa translates into increased levels of cyanobacterial toxin levels in the Great Lakes.


The centerpiece of the project is a set of three enclosure/mesocosm field manipulations that test the interactive effects of phosphorus availability and Dreissena on M. aeruginosa biomass and dominance. These factorial experiments will be conducted in Gull Lake and Lake Erie. The mechanistic component will include the development of a new theory of herbivore-phytoplankton interactions that can explain negative, positive and neutral effects of an herbivore on the abundance of a harmful phytoplankton species, quantification of selective grazing and per capita nutrient excretion by zebra mussels under widely varying environmental conditions, genetic characterizations of M. aeruginosa via HIP-PCR, and monitoring of cyanobacterial toxin production.

Progress Summary:

We have experimental evidence (ZMEX2007) that an increase in phosphorus loading changes the effect of Dreissena on M. aeruginosa biomass.  At low P levels, the effect of Dreissena was significantly positive, whereas at higher P levels there was no significant Dreissena effect.  One possible explanation for these results is a change in Dreissena 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 Dreissena grazing rates were negatively related to microcystin quota.  Monitoring data from Lake Erie in 2007 showed that the relationship between microcystin concentration and M. aeruginosa biomass in the western basin was very similar to that in the ZMEX2007 enclosures and Gull Lake, even though Lake Erie concentrations at some sites were an order of magnitude higher than in Gull Lake.  In addition, there was a strong positive relationship between biomass and TP concentration across the trophic gradient in the western basin in 2006.  However, we observed no change in microcystin quota across the gradient.  The latter may be a consequence of a lack of strong N limitation in the western basin, in contrast to the ZMEX2007 enclosures.  In the laboratory, we have found that 1) multiple genotypes of M. aeruginosa coexist in Gull Lake and that these genotypes may vary considerably in growth rate and palatability to zebra 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.

Expected Results:

We will determine whether the effect of D. polymorpha on M. aeruginosa changes direction across a broad gradient of phosphorus loading, and if so seek to identify critical loading thresholds that can be applied in the management of invaded habitats. We expect to achieve a better general understanding of the mechanisms underlying herbivore-nutrient-phytoplankton interactions. Measurements of toxin levels will directly quantify a potentially critical threat to public health, and when coupled to genetic characterizations of Microcystis, should further our ability to predict when and where toxic blooms are likely to occur in Dreissena-infested habitats. Our research may begin to shed light on the question of why Microcystis aeruginosa appears to be uniquely responsive to Dreissena invasion relative to other phytoplankton species.

Future Activities:

In 2008, we will continue  to analyze results from 2005-2007 with an emphasis on 2007, conduct another enclosure experiment in Gull Lake, and collect a third year of data from the western basin of Lake Erie.  We are also excited to expand application of the new method we have developed for measuring the growth rate of individual phytoplankton colonies, and test hypotheses that have been generated by ZMEX2007.  We also expect to partner with GLERL again in 2008 to further investigations into the role of N limitation in toxin production and M. aeruginosa growth (in both the field and laboratory), the role of toxin quota as a driver of mussel selectivity, the effect of nutrient addition on the genetic structure of the Gull Lake M. aeruginosa population and the relationship between N and P availability on M. aeruginosa biomass and toxin production in the western basin of Lake Erie.

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 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
  • Journal Article Wilson AE, Kaul RB, Sarnelle O. Growth rate consequences of coloniality in a harmful phytoplankter. PLoS One. 2010;5(1):e8679. R831708 (2007)
  • Full-text from PubMed
  • Abstract from PubMed
  • Associated PubMed link
  • Full-text: PLoS One-Full test
  • Abstract: PLoS One
  • 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, algal bloom detection, human health, grazing and window opportunities

    Relevant Websites:

    http://www.fw.msu.edu/~sarnelle/index.html Exit

    Progress and Final Reports:

    Original Abstract
  • 2006
  • Final Report