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Assessment and Significance of Phytoplankton Species Composition within Chesapeake Bay and Virginia Tributaries through a Long-Term Monitoring Program

Harold G. Marshall, Michael Lane and Todd A. Egerton

Department of Biological Sciences, Old Dominion University, Norfolk, Virginia

Virginia phytoplankton monitoring began in 1985 as a component of the Chesapeake Bay Monitoring Program and continues to include monthly surveys of the lower Chesapeake Bay and 4 of its major tributaries. Emphasis has been placed on species composition, abundance, distribution, productivity, long-term trends, and relationships to water quality and flow conditions in this region. Through this program over 1400 taxa have been identified, of which 35 are known as potential harmful species to fish, shellfish, or humans. The phytoplankton will pass through seasonal successional stages where various components are the major contributors in abundance and biomass. Major determiners in development are nutrient concentrations (ca. nitrogen, phosphorus), available light, and periods of high and low river flow. Greatest productivity ( 14C) occurs during summer when increased concentrations of autotrophic picoplankton augment the other phytoplankton populations. Many long term trends are favorable and include significant increased growth of diatoms and chlorophytes, but these patterns vary within different salinity regions and seasons. Of concern is increased dinoflagellate development in the lower reaches of these rivers and Bay, where algal blooms generally have a broader area and duration of development. Major negative patterns are increased trends in the biomass and abundance of cyanobacteria, especially since several toxic species are in this group. These include Microcystis aeruginosa, which is a producer of the toxin microcystin. Blooms of this species are becoming more common and extensive in their development over the past decade, especially within the tidal fresh and oligo-mesohaline regions of rivers entering the Bay.

Keywords: Chesapeake Bay, phytoplankton, Microcystis aeruginosa.

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