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GLERL 2000 Milestone Reports
GOAL: SUSTAIN HEALTHY COASTS
Objective: Protect, Conserve, and Restore Coastal Habitats and Their Biodiversity
PM: Number or U.S. coastal regions with reduced introductions and impacts of non-indigenous species.
Milestone: Determine whether the interaction of zebra mussels with nutrient dynamics in mussel-infested areas of the Great Lakes is a significant factor in the development of blue-green algal blooms in those areas.
Scientist: H.A. Vanderploeg
Purpose: A number of blooms of Microcystis, a toxic colonial blue-green alga that also causes taste and odor problems in drinking water, occurred on Saginaw Bay and Lake Erie as well as on inland lakes following the establishment of zebra mussel populations. In earlier work, we demonstrated that selective filtering by the mussels was a probable cause of blooms. This research was undertaken to determine whether nutrient excretion by the mussels also contributed significantly to initiating and sustaining a bloom. If nutrient excretion decreased the N:P (nitrogen:phosphorous) ratio in the water through higher excretion of P than the N:P ratio of the algae ingested then Microcystis and other blue-green algae could be favored for growth because blue-green algae prefer low N:P ratios.
Efforts: A series of experiments were performed on Saginaw Bay which has a low P concentration in water and Lake Erie which has a high P concentration in water to examine N and P excretion of the mussels as a function of algal species composition, N:P ratio of the algae and other seston, and mussel ingestion of C, N, and P.
Customers: Great Lakes water quality managers.
Significance: Understanding the cause of blue-green blooms will help mangers develop effective strategies to prevent blooms of algae that cause taste and odor problems.
Success: The project is complete and a manuscript giving our findings is now in preparation. This work demonstrated that nutrient excretion is a secondary factor relative to selective grazing for enhancing growth of toxic algae in the Great Lakes. In fact, in P-poor systems such as Saginaw Bay, P tends to be retained by the zebra mussels rather than excreted thus, the excretion products of the zebra mussel have a higher N:P ratio.
Next Steps: Complete the manuscript. The results of these studies brings this line of work to a conclusion. Additional work through regional collaborations is continuing to investigate issues related to selective feeding as the driving force for blue-green algal blooms.
Last updated: July 9, 2002 mbl