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Project 16

Project title: Complex interactions between harmful phytoplankton and grazers: variation in zebra mussel effects across nutrient gradients (EPA Grant Number: R831708)
Invesigators and Institutions:
    Orlando Sarnelle, Michigan State University, East Lansing, MI, sarnelle@msu.edu
    Stephen Hamilton, Michigan State University, Hickory Corners, MI, hamilton@kbs.msu.edu
    Joan Rose, Michigan State University, East Lansing, MI, rosejo@msu.edu
    Scott Peacor, Michigan State University, East Lansing, MI, peacor@msu.edu
    Henry Vanderploeg, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, Henry.Vanderploeg@noaa.gov

EPA Project Officer: Gina Perovich
Project Period: January 1, 2005 through December 31, 2007
Project Amount:  $ 454,779
Research Category:  Ecology and Oceanography of Harmful Algal Blooms

Description:
Filamentous and colonial cyanobacteria are the most important taxa causing harmful phytoplankton blooms in freshwater.  A long-standing tenet in lake ecology is that summer blooms of harmful cyanobacteria are a characteristic response to nutrient enrichment and a symptom of eutrophication.  However, recent events in the Great Lakes region suggest that the invasion of the zebra mussel (Dreissena polymorpha) is altering well-established functional relationships between nutrient loading and cyanobacterial dominance via the promotion of Microcystis aeruginosa, a toxic species of cyanobacteria, in low-nutrient lakes.  We examine the interaction between D. polymorpha and M. aeruginosa with large-scale field manipulations of mussel density and nutrients coupled to research aimed at elucidating underlying mechanisms.

Objectives/Hypotheses:
1)     experimentally determine whether the effect of D. polymorpha on M. aeruginosa changes direction across a broad gradient of phosphorus loading
2)     identify thresholds in P loading at which the D. polymorpha effect changes direction
3)     understand the mechanisms underlying the complex interaction between D. polymorpha 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 D. polymorpha and M. aeruginosa in the western basin of Lake Erie
5)     determine the extent to which D. polymorpha promotion of M. aeruginosa translates into increased levels of cyanobacterial toxin levels in the Great Lakes

Approach:
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.

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.

Supplemental Keywords:
water, drinking water, health effects, ecological effects, population, natural toxins, ecosystem, aquatic, marine science, limnology, biology, ecology, modeling, monitoring, measurement methods, Great Lakes, Midwest, Michigan, MI, exotic species, cyanobacteria, bluegreen algae, phytoplankton