Grantee Research Project Results
2008 Progress Report: The Impact of Nutrients, Zooplankton, and Temperature on Growth of, and Toxin Production by, Cyanobacteria Blooms in the Upper Reaches of Chesapeake Bay
EPA Grant Number: R833220Title: The Impact of Nutrients, Zooplankton, and Temperature on Growth of, and Toxin Production by, Cyanobacteria Blooms in the Upper Reaches of Chesapeake Bay
Investigators: Gobler, Christopher , Coyne, Kathryn J. , Dawson, Celia
Institution: The State University of New York at Stony Brook , Maryland Department of Natural Resources
EPA Project Officer: Packard, Benjamin H
Project Period: March 28, 2007 through March 27, 2010
Project Period Covered by this Report: March 28, 2008 through March 27,2009
Project Amount: $449,947
RFA: Ecology and Oceanography of Harmful Algal Blooms (2006) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Water
Objective:
The objective of this study was to determine if microzooplankton as well as mesozooplankton, including laboratory-reared cladocerans (Daphnia pulex) and amphipods (Hyalella azteca) and the natural community of mesozooplankton, were able to effectively graze on toxic and non-toxic strains of Microcystis during natural bloom events.
Progress Summary:
PART I. Grazing by mesozooplankton and microzooplakton on toxic and non-toxic strains of the harmful cyanobacterium, Microcystis during bloom events in the tributaries of Chesapeake Bay
Most harmful algae synthesize toxins, some of which have been hypothesized to serve as grazing deterrents. With regard to cyanobacteria, the ability of the harmful cyanobacteria Microcystis to synthesize microcystin, coupled with the observed low zooplankton grazing rates on this species during blooms, has led to the hypothesis that this compound inhibits zooplankton grazing. Testing this hypothesis in an ecosystem setting has proved challenging as Microcystis blooms are comprised of microscopically indistinguishable toxic and non-toxic strains which require molecular techniques to distinguish between the two sub-populatons. The objective of this study was to determine if microzooplankton as well as mesozooplankton, including laboratory-reared cladocerans (Daphnia pulex) and amphipods (Hyalella azteca) and the natural community of mesozooplankton, were able to effectively graze on toxic and non-toxic strains of Microcystis during natural bloom events. A 2-year field campaign was established in the Transquaking River, a tributary discharging into Chesapeake Bay, in which the dynamics of toxic and non-toxic strains of Microcystis were determined via quantification of the microcystin synthetase gene (mcyD) and ribosomal RNA gene, 16S. During the summer of 2007, Transquaking River hosted chlorophyll concentrations of 171 ± 47 μg L-1 and an overall range of 64.5 to 386 μg L-1. Microcystis was detectable using molecular techniques on every date sampled with dominance shifting between toxic and non-toxic strains throughout the summer. During an October bloom, both toxic and non-toxic strains reached peak densities of 4.0 ± 1.5x106 cell equivalents L-1and 2.7 ± 0.59x107 cell equiv. L-1, respectively. Furthermore, microcystin concentrations ranged from 0.75 to 6.8 μg L-1 with peak concentrations coinciding with peak toxic Microcystis cell equivalents. During the summer of 2008, chlorophyll a concentrations ranged from 77 to 2090 μg L-1 with mean concentrations of 427 ± 239 μg L-1. Similar to 2007, Microcystis was detected on every date sampled with toxic Microcystis dominating from late May through early July with peak densities of 2.8 ± 0.23 x108 cell equiv. L-1 occurring in late May. From mid-July on, dominance shifted towards non-toxic strains of Microcystis which remained dominant throughout the remainder of the field season reaching peak densities of 3.9 ± 1.9 x107 cell equiv. L-1 in late August. Dilution experiments showed that in 5 of 6 of experiments conducted, the microzooplankton community was able to graze on the total Microcystis community. Furthermore, the microzooplankton community was able to graze on both toxic and non-toxic strains of Microcystis. Nontoxic Microcystis was successfully grazed in 83% experiments, whereas toxic Microcystis was grazed in only 50%. The mean grazing rates on the toxic and non-toxic strains were 1.5 ± 0.52 d-1 and 0.98 ± 0.27 d-1, respectively, indicating that when grazing was occurring on both populations the microzooplankton grazed better on the non-toxic strains of Microcystis. Similarly to the microzooplankton, an 8x increase in the natural population of mesozooplankton was able to graze on the total Microcystis population (0.11 ± 0.05 d-1) in 88% of experiments conducted. The natural community of mesozooplankton was able to graze the toxic strains and non-toxic strains of Microcystis in 75% of experiments conducted. Mean grazing rates on toxic and non-toxic strains were 0.19 ± 0.08 d-1 and 0.09 ± 0.03 d-1, respectively. D. pulex was able to graze both toxic and non-toxic strains of Microcystis in 33% and 50% of experiments, respectively. Mean grazing rates on toxic and non-toxic strains were similar at 0.02 ± 0.005 individual-1 d-1and 0.02 ± 0.005 individual-1 d-1. Furthermore, H. azteca was able to graze on both toxic and non-toxic strains of Microcystis in 33% and 16% of experiments, respectively. Mean grazing rates on toxic and non-toxic strains were 0.19 ± 0.07 individual-1 d-1 and 0.03 ± 0.03 individual-1 d-1, respectively. In conclusion, this study found that both microzooplanton and mesozooplankton are able to graze on toxic and non-toxic strains of Microcystis and that microzooplankton are better grazers of both strains of Microcystis than either cultured or natural populations of mesozooplankton.
PART II. The impacts of nitrogen loading on the growth and proliferation of toxic and non-toxic strains of Microcystis during bloom events in the tributaries of Chesapeake Bay
Although P limits has traditionally been thought to limit phytoplankton growth in freshwater ecosystems, recent ecosystems studies have demonstrated that N loading can promote Microcystis blooms. Moreover, recent laboratory studies have shown that toxic strains of Microcystis outgrown nontoxic strains at higher levels of N. The impact of N enrichment on toxic and non-toxic strains of Microcystis in an ecosystem setting has yet to be explored, and the relative importance of organic and inorganic N compounds in promoting Microcystis blooms is unknown. We conducted a series of field experiments to address these questions. In 88% (7 of 8) of experiments conducted in Chesapeake Bay tributaries, at least one form of nitrogen (N) significantly increased the growth rate of the total phytoplankton community above the control treatments (p < 0.05). More specifically, the addition of nitrate yielded a significantly increased growth rate in 83% of the experiments where any form of N yielded an enhanced growth rate (p < 0.05). Furthermore, in 80% of the experiments where nitrate addition treatment increased phytoplankton growth rate, it led to the highest growth rate of any treatment (-0.11 ± 0.03 d-1 to 0.13 ± 0.02 d-1; p < 0.05). Also, the additive treatment of nitrate and phosphate significantly enhanced phytoplankton growth rates in 50% of experiments where any form of N increased growth rate (p < 0.05). Urea also enhanced the growth rate of the total phytoplankton community in 33 % of experiments conducted with grazing rates ranging from 0.13 ± 0.01 d-1to 0.10 ± 0.01 d-1. Finally, in no experiment did an increase in P alone yield a significantly increased growth rate for the total phytoplankton community, indicating that this community was never limited by phosphorus during the summer of 2008. Similarly to the total phytoplankton community, at least one form of nitrogen yielded significantly increased growth rates for the total cyanobacterial community in 88% (7 of 8) experiments conducted (p < 0.05). However, conversely to the total phytoplankton population, the additive treatment of nitrate and phosphate lead to significantly higher growth rates in 86% (6 of 7) experiments conducted (p < 0.05) and typically the highest growth rate of any treatment. Growth rates ranged from 0.21 ± 0.00 d-1 to 0.34 ± 0.02 d-1. Also, increases in L-glutamine concentrations lead to significantly enhanced growth rates in 71% experiments (p < 0.05). Growth rates within this treatment ranged from 0.13 ± 0.02 d-1 to 0.25 ± 0.00 d-1. Furthermore, nitrate, urea, and ammonium all yielded significantly increased growth rates in 57% of experiments conducted (p < 0.05). Finally, in only one experiment did an increase in P concentrations yield a significantly increased growth rate in the total cyanobacterial community. Overall, these data suggest that both total phytoplankton population and the cyanobacterial community are primarily N limited in Transquaking River. It also suggests that the cyanobacterial community might be able to better assimilate diverse types of nitrogen, including organic forms than the overall phytoplankton community. Presently, analyses are underway to assess the specific responses of toxic and non-toxic strains of Microcystis using qPCR targeting gene sequences specific for the 16S and mcyD genes in this genus.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 1 publications | 1 publications in selected types | All 1 journal articles |
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Davis TW, Berry DL, Boyer GL, Gobler CJ. The effects of temperature and nutrients on the growth and dynamics of toxic and non-toxic strains of Microcystis during cyanobacteria blooms. Harmful Algae 2009;8(5):715-725. |
R833220 (2008) |
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Supplemental Keywords:
Zooplankton, cyanobacteria blooms, Chesapeake Bay, microzooplankton, mesozooplankton , RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Oceanography, algal blooms, Environmental Monitoring, Ecology and Ecosystems, marine ecosystem, bloom dynamics, HAB ecology, water quality, algal bloom detectionProgress 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.