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OBJECTIVES: To understand the predator-prey interactions between phytoplankton, microzooplankton, and copepods before and during a winter dinoflagellate bloom. Investigate how zooplankton grazing rates influence the formation of a winter bloom and in turn how the winter bloom influences zooplankton abundances.
METHODOLOGY: The Landry-Hasset dilution technique will be used to determine the phytoplankton growth rates and microzooplankton grazing rates. Incubations with and without copepods will be used to collect data so copepod grazing rates can be calculated with the Frost equations. Primary production from phytoplankton will be determined by measuring the change in O2 over a 24 hour period for bottles exposed to light and those kept in the dark.
RATIONALE: A winter dinoflagellate bloom in a Chesapeake Bay tributary can account for a large portion of annual primary production in the system, so my research will focus on grazing rates of microzooplankton and copepods on the bloom to predict what the fate of the new carbon is. Fish such as Striped Bass come up to tributaries, where winter blooms occur, and spawn. If the winter bloom has a positive impact on the copepod population at the right time it can lead to a higher recruitment of the fish. The other possibilities are that the winter bloom has no impact on the copepod population or the timing of increase in copepod abundance is off from fish spawning. This project will suggest whether the abundance and timing of the winter dinoflagellate bloom can be used to predict spring fish recruitment.
This section describes how this project has advanced scientific knowledge and/or made a difference for coastal residents, communities, and environments. Maryland Sea Grant has reported these details to the National Oceanic and Atmospheric Administration (NOAA), one of our funding sponsors.
Summary: Researchers quantified winter blooms of a dinoflagellate species in Chesapeake Bay that can play an important role in the food web that supports the estuary’s population of striped bass, a commercially important fishery. The research indicated that improved monitoring of the winter blooms could help improve understanding of annual variation in the striped bass population and refine management of this fishery.
Relevance: The size of the annual recruitment of commercially important fish such as striped bass in Chesapeake Bay depends on a food web that includes phytoplankton, zooplankton, and copepods. Typically resource managers have assumed that algal blooms do not occur during winter months and so have not monitored phytoplankton at that time. However, winter blooms of plankton (dinoflagellates) have been observed in the Chesapeake since the 1970s. The Chesapeake Bay’s dominant copepod, Eurytemora carolleeae, feeds on these dinoflagellates in Chesapeake Bay tributaries where the winter blooms occur. Eurytemora carolleeae are a key food source for larvae of commercially important fish species like striped bass, which spawn in the bay’s tributaries in springtime. These copepods that hatch in winter take three to four months to mature and likely become the prey for striped bass larvae in springtime. Research that describes winter dinoflagellate blooms and the response of predators in the food web that feed on them can potentially inform management of commercial fish populations.
Response: Nicole Millette, a graduate student at Horn Point Laboratory of the University of Maryland Center for Environmental Science who was funded by a Maryland Sea Grant fellowship, estimated the rate at which the copepod E. carolleeae ingests the dinoflagellate Heterocapsa rotundata in winter. The project included an outreach component to provide professional development for high-school teachers and mentoring for their students.
Results: The researchers demonstrated the importance of winter dinoflagellate blooms in the food web that supports striped bass. The researchers found that a winter bloom of H. rotundata dinoflagellates was associated with an increase in the E. carolleeae copepod population the following spring. The researchers also found that E. carolleeae preferentially consumed H. rotundata as prey and, as a result, survival of E. carolleeaen auplii (an early stage of development) increased in winter and abundances of E. carolleeae copepodites (a later stage) increased in spring. The ability to more accurately predict striped bass recruitment may partially depend on a better understanding of winter dinoflagellate blooms of H. rotundata and their effect on E. carolleeae abundance. Researchers offered to share their data with the Chesapeake Bay Program Office.
Millette, NC; Stoecker, DK; Pierson, JJ. 2015. Top-down control by micro- and mesozooplankton on winter dinoflagellate blooms of Heterocapsa rotundata. Aquatic Microbial Ecology76:15 -25. doi:10.3354/ame01763. UM-SG-RS-2015-07.