Grantee Research Project Results
2005 Progress Report: Complex Interactions Between Harmful Phytoplankton and Grazers: Variation in Zebra Mussel Effects Across Nutrient Gradients
EPA Grant Number: R831708Title: Complex Interactions Between Harmful Phytoplankton and Grazers: Variation in Zebra Mussel Effects Across Nutrient Gradients
Investigators: Sarnelle, Orlando , Rose, Joan B. , Vanderploeg, Henry , Peacor, Scott , Hamilton, Stephen
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, 2004 through December 31, 2005
Project Amount: $454,779
RFA: Ecology and Oceanography of Harmful Algal Blooms (2004) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Water
Objective:
The objectives of this research project are to: (1) experimentally determine whether the effect of Dreissena on Microcystis aeruginosa changes direction across a broad 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; and (5) determine the extent to which Dreissena promotion of M. aeruginosa translates into increased levels of cyanobacterial toxin levels in the Great Lakes.
Progress Summary:
We conducted a large-scale field experiment during the summer of 2005 in Gull Lake, an oligotrophic lake adjacent to the Kellogg Biological Station that was invaded by Dreissena in 1994 (see Figure 1). Two treatments were applied in the field experiment, three levels of nutrients and the two levels (presence/absence) of Dreissena, in a fully factorial design. Unfortunately, Dreissena survival in the field experiment was poor after the first few weeks, so the long-term effects of Dreissena at different nutrient levels could not be determined in this experiment. We will repeat the experiment in 2007 with revised protocols that will ensure long-term Dreissena survival.
Figure 1. Photograph of the 2005 Field Experiment in Gull Lake
Nutrient enrichment with NaPO4 and NaNO3 (atomic N:P ratio of 20) was highly effective at increasing total phytoplankton biomass (as chlorophyll a) over the course of the field experiment (see Figure 2). Despite the strong positive response of phytoplankton growth to nutrient enrichment in the field experiment, preliminary results suggest that there was little response by M. aeruginosa to fertilization. This assessment is based on the fact that there was no effect of nutrient treatment on microcystin concentrations in the enclosures (see Figure 3). Thus, we will turn our attention to the response of M. aeruginosa to different types of nutrient fertilization during the 2006 field season, in addition to developing improved methods of handling Dreissena that ensures the long-term survival of mussels in field experiments.
Figure 2. Effects of the Nutrient-Enrichment Treatments (0 = no addition, medium ≈ 20 μg/L total phosphorus [TP], high ≈ 40 μg/L TP) on Total Phytoplankton Biomass (as chlorophyll a) in the 2005 Field Experiment. Results for day 39 of the experiment are shown.
We have initiated a new collaboration between Michigan State University and the National Oceanic and Atmospheric Administration/Great Lakes Environmental Research Laboratory (NOAA/GLERL) via the Center of Excellence for Great Lakes and Human Health (funded by NOAA) to enhance our ability to assess how nutrients and Dreissena affect the genetic structure of M. aeruginosa populations. We are collaborating with Juli Dyble, an expert in cyanobacterial genetics, who is now at GLERL. We isolated 25 individual colonies from each enclosure at the end of the 2005 field experiment for genetic analysis. Colonies were transferred through four washings of membrane-filtered lake water before being pipetted into microtubes. Colonies are currently in frozen storage awaiting genetic analysis. The genetic data will test whether nutrient enrichment affects the genetic structure of M. aeruginosa populations and specifically how nutrient enrichment affects the representation of toxin-capable strains (i.e., possessing the mcyB gene) in the Gull Lake population.
Figure 3. Effects of the Nutrient-Enrichment Treatments (0 = no addition, medium ≈ 20 μg/L TP, high ≈ 40 μg/L TP) on Microcystin Concentrations in the 2005 Field Experiment. Results for day 45 of the experiment are shown.
Future Activities:
The first task for the 2006 field season is to develop a protocol for stocking Dreissena into experimental enclosures that minimizes their subsequent mortality. We have already ruled out several factors as causes of the high mortality we observed in the 2005 field experiment, including: (1) the removal of mussels from rocks by cutting byssal threads; (2) potential toxicity of the materials used to construct the enclosures or the cages in which the mussels are housed; (3) exposure of mussels to high light intensities; and (4) the relatively large size of the mussels selected for stocking into the enclosures. In Year 2, we will examine the following potential mortality factors: (1) the local density of mussels stocked into each cage; (2) the degree of water exchange around caged mussels; and (3) the degree of cage movement in the enclosures. Each of these factors will be varied experimentally for groups of mussels stocked into enclosures. We will compare the survival of mussels stocked into enclosures with that of mussels that are handled identically but incubated in cages in the lake.
In previous years, we have established that mussels housed in experimental cages and incubated on the lake bottom suffer little mortality over the entire summer.
We have formulated two hypotheses to explain why M. aeruginosa growth did not respond strongly to our nutrient (PO4 plus NO3) additions in 2005 yet showed a positive response to additions of PO4 alone, in the presence of Dreissena, in a field experiment we conducted in Gull Lake in 2001. The first hypothesis concerns the ratio of N:P added (20 in 2005, 0 in 2005), the second concerns the form of N added (NH4 versus NO3). During the summer of 2006, we will conduct a field experiment in Gull Lake in which we vary N:P ratio and nitrogen source (NH4+ versus NO3-). At the end of this experiment, we will isolate individual colonies for genetic analysis, as well as monitor toxin concentrations and M. aeruginosa biomass.
Efforts to develop mechanistic models of the Dreissena-cyanobacteria interaction recently have been enhanced by the hiring of a dedicated postdoctoral fellow who will work under the direction of Scott Peacor. The postdoctoral fellow is funded by GLERL to work on the Ecology of Harmful Algal Blooms project and will arrive in October 2006. We expect significant progress on this objective in the fall of 2006.
Journal Articles:
No journal articles submitted with this report: View all 9 publications for this projectSupplemental Keywords:
drinking water, health effects, ecological effects, population, natural toxins, marine science, modeling, measurement methods, exotic species, cyanobacteria, bluegreen algae, phytoplankton,, 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 opportunitiesRelevant Websites:
http://www.fw.msu.edu/people/sarnelle/index.html Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.