Date of Award

Summer 1990

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Ecological Sciences

Committee Director

H. G. Marshall

Committee Member

Kneeland Nesius

Committee Member

Andrew S. Gordon

Committee Member

William Dunstan

Committee Member

James Melchor


This study was performed to evaluate phototrophic pico-plankton (0.2 to 2.0 μm) dynamics within the lower Chesapeake Bay. A 15 month study of phototrophic picoplankton abundance and productivity was made from June 1988 to October 1989. Annual picoplankton abundance using epifluorescence microscopy ranged from 7.26 x 106 cells/1 in the winter to 9.28 x 108 cells/1 during late summer.

In situ incubations of natural picoplankton populations over the 15 month study were used to test the applicability of the frequency of dividing cells technique in estimating phototrophic picoplankton growth rates. The regression equation o fμ = 2.37 x 10-3 (FDC) + 0.024 was developed to estimate phototrophic picoplankton growth rates in the lower Chesapeake Bay where productivity values were estimated using phototrophic picoplankton abundance and carbon content. Limitations and improvements in using the frequency of dividing cells technique were discussed. Productivity estimates using both frequency of dividing cells and sodium 14C-bicarbonate fractionation techniques identified phototrophic picoplankton contributing over 50% of total primary productivity during the summer season.

Two high frequency diel studies measuring phototrophic picoplankton abundance and productivity in summer and winter seasons revealed physical factors in the water column partly determining phototrophic picoplankton distribution. Higher phototrophic picoplankton concentrations were associated with waters seasonally above the pycnocline. In summer, phototrophic picoplankton concentrations were highest during ebb tide when the dominant phototrophic picoplankton was phycocyanin enriched Synechococcus sp. In winter, phototrophic picoplankton concentrations were highest during flood tide when phycoerythrin enriched Synechococcus sp. dominated phototrophic picoplankton composition. Availability of phototrophic picoplankton carbon within the water column is discussed as to its influence to Bay trophodynamics.


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