Grantee Research Project Results
2004 Progress Report: Grazing and Windows of Opportunity for Dinoflagellate Blooms
EPA Grant Number: R829366Title: Grazing and Windows of Opportunity for Dinoflagellate Blooms
Investigators: Stoecker, Diane K. , Boicourt, William C. , Roman, Michael R.
Institution: University of Maryland Center for Environmental Science
Current Institution: University of Maryland Center for Environmental Science , Horn Point Laboratory
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 2002 through December 31, 2004
Project Period Covered by this Report: January 1, 2004 through December 31, 2005
Project Amount: $428,184
RFA: Ecology and Oceanography of Harmful Algal Blooms (2001) RFA Text | Recipients Lists
Research Category: Water , Aquatic Ecosystems
Objective:
When conditions (light, temperature, and nutrients) are suitable for dinoflagellate growth, grazing may prevent population increases and bloom formation. The main objectives of this research project are to:
- determine if windows of opportunity occur when and where grazing pressure is low on small (< 25 micron) dinoflagellates;
- determine if these windows are a necessary condition for the initiation of blooms;
- and define the physical and chemical conditions that can create these windows.
Progress Summary:
To investigate the role of grazing, or lack thereof, in the formation of dinoflagellate blooms, cruises were conducted in 2002, 2003, and 2004 in the Choptank and Paxtuxent Rivers, two tributaries of the Chesapeake Bay, in which blooms often occur in late April or early May. Sampling started in late February/early March so that the set-up period for blooms would be included. Sampling was extended through late May and then into June when we thought that the bloom might be late because of weather conditions. Data were collected on irradiance, temperature, salinity, inorganic nutrients, turbidity, and chlorophyll a, an indicator of phytoplankton biomass. These data are being used to describe the bottom-up controls on dinoflagellate growth, such as nutrient and light availability, temperature, and the potential affects of water residence time on dinoflagellate populations.
At three experimental stations on each river, samples were collected to determine the abundance of dinoflagellates and their potential microzooplankton and mesozooplankton grazers. To determine if windows of low grazing occurred, microzooplankton and copepod grazing experiments were conducted with natural assemblages from the experimental stations. Two bloom-forming dinoflagellates, Prorocentrum cordatum (P. minimum) and Karlodinium micrum, were used as prey in the microzooplankton grazing experiments. Copepod grazing on phytoplankton, as well as on microzooplankton grazers in natural assemblages, was determined so that the direct affects of copepod grazing on dinoflagellates could be evaluated. Indirect affects of copepod grazing on dinoflagellates from predation of copepods on the microzooplankton grazers of dinoflagellates that might lead to a reduction in total community grazing pressure on dinoflagellates (i.e., a trophic cascade) were evaluated.
The first sampling year, 2002, was a record drought year. The extremely low fresh-water flow resulted in record high salinity, low nutrient input, and low phytoplankton biomass. The estuary temporarily returned to a less eutrophic state, and the usual spring dinoflagellate blooms were not observed in the Choptank and Paxtuxent Rivers. During 2002, bottom-up control caused by low nutrients prevented blooms, but potential microzooplankton grazing on dinoflagellates remained high. There was, however, an increased abundance of the diatoms in the genus Pseudo-nitzschia, a genus of diatoms that can produce domoic acid, the toxin responsible for Amnesic Shellfish Poisoning (ASP) and Domoic Acid Poisoning (DSP). Pseudo-nitzschia strains were isolated from the Choptank River and Chesapeake Bay, and several strains were identified as toxic species and domoic acid production was confirmed in the laboratory. These data suggest that if increased climate variability results in frequent droughts in the Chesapeake watershed, ASP and DSP might become concerns to the health of human and animal populations in the Chesapeake Bay area.
The second year, 2003, was a record high fresh-water flow year. Surface salinities were much lower and inorganic nutrients were much higher than average for this season in both rivers. Because of the high flow rates, residence times were short in both rivers, which may have hindered the development of resident plankton populations. Although small blooms of Heterocapsa triquetra and H. rotundatum occurred in March 2003 and a small P. minimum bloom in May 2003 in the lower Choptank, we did not observe dense, extensive blooms in association with the high nutrient loads. Our results indicate that mesozooplankton grazing on dinoflagellates was high in early spring and contributed to the demise of the Heterocapsaspp. blooms. In late April and early May, microzooplankton potential grazing on dinoflagellates was high, but spatially variable. Our data suggest that microzooplankton grazing helped to prevent a bloom of K. micrum in May 2003. Although average microzooplankton grazing pressure on P. minimum appeared to be high enough to prevent net growth of populations, a small, spatially limited bloom of this species occurred. It is possible that the mini-bloom was supported by recruitment of cells from the pycnocline or that the high spatial variability in grazing pressure and dinoflagellate populations allowed sub-populations to escape grazing.
In the third year of our study, freshwater flow conditions were closer to normal. Samples and data from this season currently are being analyzed.
Our data analyses to date support the importance of both top-down and bottom-up controls on spring dinoflagellate blooms in estuaries. Comparison of the record dry and wet years indicate that when nutrient input is reduced because of low flow, estuaries can rapidly return to a less eutrophic state with tight top-down and bottom-up controls on phytoplankton growth. During record high flow years, the development of blooms can be hindered by low residence times and perhaps light limitation as well as by grazing.
Future Activities:
We are currently completing sample and data analysis from 2004. Sample and data analysis and manuscript preparation will proceed as planned.
Journal Articles:
No journal articles submitted with this report: View all 22 publications for this projectSupplemental Keywords:
marine, estuary, ecosystem, ecology, monitoring, Chesapeake Bay, Maryland, MD, marine science, aquatic, ecosystem protection/environmental exposure & risk, geographic area, scientific discipline, water, biology, east coast, ecological risk assessment, ecology and ecosystems, oceanography, algal blooms, Choptank River, harmful algal blooms, HAB ecology, Paxtuxent River, dinoflagellate blooms, dinoflagellates, estuaries, grazing and window opportunities,, RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, State, Oceanography, algal blooms, Ecological Risk Assessment, Ecology and Ecosystems, Biology, Chesapeake Bay, East Coast, microbiology, dinoflagellates, estuaries, ecology, Patuxent River, HAB ecology, Choptank River, Maryland (MD), water quality, grazing and window opportunitiesRelevant Websites:
http://hpl.umces.edu/faculty/stoecker/stoeckerlab.htm 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.