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This project is no longer current

The Role of Zebra Mussels in Promoting Microcystis Blooms and Other Ecosystem Changes in Saginaw Bay and in Lake Erie

Primary Investigator:

Henry Vanderploeg - NOAA GLERL



This research project stems from GLERL’s Saginaw Bay Zebra Mussel Program (1991-1996) which evaluated the effects of Zebra mussels on ecosystem structure and function. This specific project explores hypothesized mechanisms of Microcystis bloom creation by Zebra mussels using statistical and dynamic modeling.


  1. Collated individual data sets into easy to use Microsoft Access database
    • phytoplankton
    • zooplankton
    • benthos
    • nutrients
    • physical variables
  2. Cultivated collaborations with external research partners who provided:
    • fish data
    • expertise in statistical and dynamic modeling
    • diagnostic analysis on nutrient cycling using dynamic mass-balance model


Because of their high abundance and very high filtering rates in shallow aquatic systems, Zebra mussels remove a significant portion of the primary production. In some shallow experimental lakes in Europe, introduced Zebra mussels have improved water clarity and macrophyte growth, and it has been argued that they can improve the quality of the algal resource base so that food web efficiency and fish production can be increased. As a result, some scientists have advocated introduction into other aquatic systems. Improvement of water clarity has been seen in Lakes Erie and St. Clair; however, in Lake St. Clair, the increased water clarity may have contributed to massive blooms of vascular macrophytes that have washed up on shore and fouled beaches. In the inner portion of Saginaw Bay, water clarity improved in midsummer of 1991 and 1993; but in 1992, 1994, and 1995 there were marked decreases in water clarity owing to massive blooms of Microcystis, a potentially toxic colonial cyanobacterium, or blue-green alga. Blooms of Microcystis also occurred in western Lake Erie in 1995 and 1998. In addition, there have been outbreaks of near-bottom blooms of the filamentous alga Spirogyra, which have later washed up on beaches.

In addition to the blooms, we were interested in describing and explaining other mussel-induced changes in the Saginaw Bay ecosystem from experimental work and extensive monitoring of nutrients, phytoplankton, zooplankton, and benthos during 1990-1996.

From 1991-1996 GLERL carried on an extensive monitoring and experimental program to document and explain the effects of Zebra mussels on the Saginaw Bay ecosystem. Much of the experimental work and description of ecosystem change for the years 1991-1993 was published in a special volume of J. Great Lakes Res. These studies documented, for example, the rapid increase in Zebra mussel populations that increased water clarity, reduced chlorophyll concentration and primary production in the water column due to Zebra mussel filtering.

Juli Dyble sampling Microcystis bloomStarting in 1994 the trend of low algal standing stocks during summer was reversed with the appearance of toxic Microcystis blooms. Much of the research effort since then has been focused on how Zebra mussel selective filtering and nutrient excretion may have promoted these blooms. It was further recognized that P from some event like sediment resuspension or runoff might have been required in addition to Zebra mussel selective filtering to support the levels of observed phytoplankton blooms. In late summer of 1995, a major toxic bloom of Microcystis appeared on Lake Erie. We, as members of a larger team of investigators-headed by D. Culver of Ohio State University and supported in part by the Lake Erie Protection Fund, examined the role of mussel selective filtering and nutrient excretion in promoting Microcystis blooms in both Saginaw Bay and Lake Erie through comparative experiments with mussels and seston from both systems and from selective filtering experiments with various cultured strains of Microcystis, including an isolate of the toxic Microcystis from Lake Erie.

By doing experiments with a variety of toxic and non-toxic Microcystis strains, we have shown that Zebra mussels selective rejection operates for certain toxic strains and that this selection can promote toxic blooms of Microcystis in nature (Vanderploeg et al. 2001). We also have done experiments describing mussel selective filtering rate, feeding behavior (observed directly), physiological condition, and nutrient excretion at monthly intervals April - November in 1995 and 1996 at an inner and outer bay station of Saginaw Bay and comparative experimental work for Lake Erie and Saginaw Bay for 1997 to evaluate the role of seston C:N:P ratios and phytoplankton composition on feeding rate and nutrient excretion. These experiments, which show that Zebra mussels are very sensitive to quality of the seston and that they can increase or decrease P limitation depending on N:P ratios of the seston, need to be published.

Database Development

We developed an easily accessed data base and began analyzing the spatially rich seasonal data on phytoplankton, zooplankton, benthos, nutrients, and physical variables from the Saginaw Bay Zebra Mussel Program (1991-1996) and worked with other investigators who provided data on fishes as well as expertise in modeling (statistical and dynamic) to evaluate effects of Zebra mussels on ecosystem structure and function. Of particular interest was examining the relation between changes in phytoplankton community structure relative to Zebra mussel influences and diagnostic modeling with the SAGZM-a dynamic mass balance model that includes nutrients, 5 functional phytoplankton groups, zooplankton, and Zebra mussels-to explore hypothesized mechanisms of Microcystis bloom creation by Zebra mussels.

  • Added parameter data to the database.
  • Created multiple queries to extract data for desired parameter/ space and time.
  • Incorporated plotting functionality to allow the user to produce time series graphics for any combinations of parameter/species and sampling station.
  • Used the temporally and spatially rich data set from Saginaw Bay examine relation between mussels and phytoplankton species composition and abundance using a variety of statistical tools with aim understanding impacts of Zebra mussels on the phytoplankton community and testing the connection between mussels and Microcystis
  • Described changes in the zooplankton community structure during this time.
  • Completed manuscripts on Zebra mussel feeding and seston quality interactions and on mussel nutrient excretion and seston quality from our experiments in Saginaw Bay and Lake Erie.
  • Conducted diagnostic analysis on nutrient cycling processes using Limno-Tech’s coupled multi-class phytoplankton-Zebra mussel model (SAGZM). SAGZM is a dynamic mass balance model that represents nutrients, five phytoplankton functional groups, zooplankton and three cohort groups of Zebra mussels (Bierman et al. 2005). Numerical experiments will be conducted to explore the mechanisms responsible for the formation of Microcystis blooms in Saginaw Bay.

Related Research Progress

Progress was made on a number of different studies under this project, mostly related to data collected in Saginaw Bay between 1991 and 1996 to assess impacts of the Zebra mussel on the Saginaw Bay ecosystem.

Changes in Macroinvertebrate communities: We completed a study of benthic samples collected between 1987 and 1996 at 13 sites in both the inner and outer bay bay (Nalepa et al. 2003). Overall, Zebra mussels had no significant effect on benthic macroinvertebrate biomass in the inner bay. Abundances of some taxa such oligochaetes and sphaeriids declined, but other taxa such as the amphipod Gammarus increased such that there was no net effect of mussels. In contrast, biomass in the outer bay declined after the Zebra mussel infestation due solely to the dramatic decline in the amphipod Diporeia. Since both Gammarus and Diporeia taxa are heavily fed upon by fish, these changes will likely have an impact on the distribution and feeding habits of fish in the bay.

Phytoplankton Community Changes: We built an electronic data base for seasonal phytoplankton data collected at 13 sites (1990-1996) by building Excel files from computer output that had not been stored electronically or had only been available unprocessed count data. This database was a necessary first step in evaluating the impact of the mussels on the phytoplankton community and telling the Saginaw Bay story.

Zebra mussels and Microcystis blooms:We completed a comprehensive manuscript on Zebra mussel-Microcystis feeding interactions and their relationship to Microcystis blooms on Saginaw Bay and Lake Erie (Vanderploeg et al. 2001). The manuscript demonstrated that Zebra mussel selective rejection of toxic Microcystis resulted in promotion of toxic Microcystis blooms in Saginaw Bay and Lake Erie. The mussels took in algae of a wide variety of sizes, but rejected toxic Microcystis unharmed back to the water column in pseudofeces. The study showed the mussels selected for a strain that was toxic or unpalatable to them, and that toxic or nontoxic strains from other lakes or culture collections were readily eaten.

Zebra mussels, food quality, and nutrient excretion: Progress was also made on first drafts of two manuscripts describing Zebra mussel nutrient excretion and seston food quality interactions. The other manuscripts show that the N:P ratio excreted by the mussels depends on the N:P ratio of the food, its taxonomic composition, and feeding rate of the mussels. In systems such as Saginaw Bay with a high N:P ratio (because of low P loading) the mussels excrete much higher N:P than in the seston, thus contributing to even more P limitation. In contrast, where N:P ratios are lower, such as in Lake Erie, the mussels’ excretion tends to add more P to the system. Food quality which is determined by the composition of the algal community and its N:P ratio profoundly affects feeding rate and this in turn affects nutrient excretion. Mussels filtered at much higher rates in Lake Erie, where cryptophytes were abundant and N:P ratio was at the Redfield ratio.

Changes in zooplankton communities: We determined Saginaw Bay zooplankton lengths and converted them to dry-weight biomass by use of literature regressions of biomass vs. length, and then determined egg ratios from a selected subset of the nearly 400 samples collected. Biomass measurements are necessary to define ecosystem structure affected by the mussels. The information on biomass will be combined with zooplankton number concentrations now being compiled to define time history of spatial distribution of biomass of zooplankton at the master stations (13 sites x 2 replicates x 8 years). The egg ratios may allow detection of Zebra mussel effects on the pelagic food web. The information on biomass and lengths will be used to predict a nominal zooplankton grazing for comparison with mussel grazing. Preliminary results suggest that biomass and grazing of zooplankton are small relative to those of mussels.

Physiological study: We completed a paper on seasonal and spatial differences in the enzyme transport system (ETS) and respiration of Zebra mussels in the inner and outer bay (Fanslow et al. 2001). Objectives were to determine whether ETS might be used as a surrogate for respiration rates in this species, and also to examine metabolic activity under variable conditions of food and temperature.

Ecological forecasting of impacts of Ponto-Caspian species in the Great Lakes: We completed a major synthesis (Vanderploeg et al. 2002; Vanderploeg 2003) that describes, explains, and predicts Great Lakes ecosystem impacts of six Ponto-Caspian (region including Caspian, Black, and Azov Seas) endemic species of mussels, crustaceans, and fishes that recently invaded the Great Lakes via ballast water (Vanderploeg et al. in press). The invaders are the Zebra mussel, Dreissena polymorpha; the quagga mussel, D. bugensis; the predatory cladoceran, Cercopagis pengoi; the benthic amphipod, Echinogammarus ischnus; the round goby, Neogobius melanostomus; and the tubenose goby, Proterorhinus marmoratus. The ecology and possible mechanisms of ecosystem impact were reviewed for each species using information from a variety of studies and sites, including the Great Lakes. This information was combined with case studies of experiments and monitoring on the Great Lakes to describe ecosystem change, define the underlying invader species’ mechanisms of impact, and to predict future changes.


Bierman, V.J., Jr., Kaur, J., DePinto, J.V., Feist, T.J., and Dilks, D. 2005. Modeling the Role of Zebra Mussels in the Proliferation of Blue-green Algae in Saginaw Bay, Lake Huron. J. Great Lakes Res. 31(1):32-55.

Budd, J. W., Drummer, T. D., Nalepa, T. F., Fahnenstiel, G. L. 2001. Remote sensing of biotic effects: Zebra mussels (Dreissena polymorpha) influence on water clarity in Saginaw Bay, Lake Huron. Limnol. Oceanogr. 46: 213-223.

Fanslow, D.L, T.F. Nalepa, and T.H. Johengen. 2001. Seasonal changes in the respiratory electron transport system (ETS) and respiration of the Zebra mussel, Dreissena polymorpha, in Saginaw Bay, Lake Huron. Hydrobiologia 448: 61-70.

Johengen, T.H., T.F. Nalepa, G.A. Lang, D.L. Fanslow, H.A. Vanderploeg, and M.A. Agy. 2000. Physical and chemical variables of Saginaw Bay, Lake Huron in 1994-1996. NOAA Technical Memorandum GLERL-115.

Nalepa, T.F, Fanslow, D.L., Lansing, M.B., and Lang, G.A. 2003. Trends in the benthic macroinvertebrate community of Saginaw Bay, Lake Huron, 1987 to 1996: Responses to phosphorus abatement and the Zebra mussel, Dreissena polymorpha. J. Great Lakes Res. 29: 14-33.

Nalepa, T. F., Fanslow, D.L., Lansing, M.B., Lang, G.A., Ford, M., Gostenik, G., Hartson, D.J. 2002. Abundance, biomass, and species composition of benthic macroinvertebrate populations in Saginaw Bay, Lake Huron, 1987-96. NOAA Technical Memorandum GLERL-122. Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 32 pp.

Nalepa, T. F., Fahnenstiel, G. L., and Johengen, T. H. 1999. Impacts of the Zebra mussel (Dreissena polymorpha) on water quality: A case study in Saginaw Bay, Lake Huron. In R. Claudi and J. H. Leach [eds.] Non-indigenous Freshwater Organisms in North America; Their Biology and Impact. CRC Press, Boca Raton, FL.

Vanderploeg, H.A. 2003. Ecological forecasting of impacts of ponto-caspian species in the Great Lakes: Describing, understanding, and predicting a system in transition. In Ecological Forecasting: New Tools for Coastal and Marine Ecosystem Management. NOAA Technical Memorandum NOS NCCOS 1. N. Valette-Silver and D. Scavia (Eds.). pp. 81-84.

Vanderploeg, H. A., Nalepa, T. F., Jude, D. J., Mills, E. L., Holeck, K. T., Liebig, J. R., Grigorovich, I. A., and Ojaveer, H. 2002. Dispersal and ecological impacts of Ponto-Caspian species in the Laurentian Great Lakes. Can. J. Fish. Aquat. Sci. 59:1209-1228.

Vanderploeg, H. A., J. R. Liebig, W. W. Carmichael, M. A. Agy, T. H. Johengen, G. L. Fahnenstiel, and T. F. Nalepa. 2001. Zebra mussel (Dreissena polymorpha) selective filtration promoted toxic Microcystis blooms in Saginaw Bay (Lake Huron) and Lake Erie. Can J. Fish. Aquat. Sci. 58: 1208-1221.



zebra mussel expelling alga as pseudofeces








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Zebra mussel expelling alga as pseudofeces
(1) Mussel filtering with siphons in normal position.
(2) Excurrent siphon retracted and incurrent siphon to expel the alga as pseudofeces.
(3) Pseudofeces ejected.