Grantee Research Project Results

2002 Progress Report: Grazing and Windows of Opportunity for Dinoflagellate Blooms

EPA Grant Number: R829366
Title: 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, 2002 through December 31, 2003
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: (1) if "windows of opportunity" occur when and where grazing pressure is low on small (< 25 micron) dinoflagellates; (2) if these "windows" are a necessary condition for the initiation of blooms; and (3) the physical and chemical conditions that can create these "windows."

Progress Summary:

During spring 2002, sampling was conducted on the Choptank and Patuxent Rivers, two tributaries of the Chesapeake Bay in which dinoflagellate blooms often occur in late April or early May. We collected samples and data on more than 14 cruises. Sample analyses are in progress, and the set from the Patuxent River is almost complete. We started sampling during March, the setup period for blooms, and continued sampling through May. Spring 2002 was unusual because of the low freshwater input to the Chesapeake Bay and its tributaries. Surface salinities were much higher; however, inorganic nutrients and chlorophyll were much lower than average for this season in both rivers. No dinoflagellate blooms were evident except for a subsurface bloom of Heterocapsa triquetra in the Paxtuxent River near Benedict.

Preliminary observations indicate that phytoplankton and microzooplankton assemblages were very different than in previous years. We believe this is primarily because of the low nutrient availability. To determine if low-grazing periods occurred, we conducted microzooplankton and copepod grazing experiments on four different days in the Patuxent River and on 10 different daysin the Choptank River. On each date, incubations were conducted with plankton assemblages from three stations along the reaches in which dinoflagellate blooms typically occur. Two bloom-forming dinoflagellates, Prorocentrum minimum and Karlodinium micrum, were used in the microzooplankton grazing experiments as potential prey. Analysis of the Choptank River experimental samples is in progress, whereas analysis of the experimental samples from the Patuxent River is almost complete.

The Patuxent experiments indicate that although dinoflagellate abundance was low, potential microzooplankton grazing on dinoflagellates was usually high. During April and May, potential grazing on K. micrum was much higher than on P. minimum, the larger species. Microzooplankton, particularly ciliates, were relatively abundant, although chlorophyll levels were low. Further analyses will be necessary to determine if high microzooplankton numbers were linked to low copepod abundance. Although dinoflagellate blooms did not occur at most stations in spring 2002, these data will be useful in testing our hypotheses about the relative importance of microzooplankton and mesozooplankton as potential grazers of small dinoflagellates and about the role of top-down control by copepods in releasing small dinoflagellates from grazing pressure by microzooplankton.

We hypothesized that "windows" occur following the spring diatom bloom because microzooplankton are low in abundance at this time, because of top-down control by copepods. During 2002, a "typical" large spring diatom bloom did not occur and chlorophyll levels remained low. These conditions may, in some respects, mimic those in the Chesapeake Bay and its tributaries before pronounced anthropogenic eutrophication.

When sample and experimental analyses are complete, it will be interesting to compare our results for spring 2002 to historical data and to data from the next 2 years, when freshwater input and hence nutrient input may return to higher levels. These comparative data should provide insight into how inputs alter planktonic food webs and whether "eutrophic" or high-flow conditions are conducive to dinoflagellates blooms, not only because they provide the nutrients to support high biomass, but because of the occurrence of "windows" in grazing pressure in which high net growth of dinoflagellates can occur.

Future Activities:

We currently are completing sample and data analysis for last year's research. Two of our stations in each river are the same as stations that have been sampled over the past 20 years by the Chesapeake Bay program. To put 2002 results in context, we are statistically comparing last year's data on temperature, salinity, nutrients, chlorophyll, and possibly phytoplankton species composition to the last 20 years of data for these stations.

We will begin sampling and experiments on the Choptank and Patuxent Rivers in late February and anticipate that sampling will end in early May. Carboy experiments will be conducted this year to test the hypothesis that high copepod densities can indirectly reduce community grazing on small dinoflagellates. Sample and data analysis will proceed as planned.

Journal Articles:

No journal articles submitted with this report: View all 22 publications for this project

Supplemental Keywords:

marine, estuary, ecosystem, ecology, monitoring, Chesapeake Bay, Maryland, MD, marine science, aquatic., 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 opportunities

Relevant Websites:

http://hpl.umces.edu/faculty/stoecker/stoeckerlab.htm Exit

Progress and Final Reports:

Original Abstract

2003

Final Report