Using frequency of dividing cells in estimating autotrophic picoplankton growth and productivity in the Chesapeake Bay

In situ incubations of natural autotrophic picoplankton populations during a 15 month study were used to test the frequency of dividing cells proceduresin estimating phototrophic picoplankton growth rates. These rates were estimated using dilution experiments and compared to the average frequency of dividing cells over the same time interval. The regression equation of µ = 2.85 × 10^–3 (FDC) + 0.022 was calculated to relate autotrophic picoplankton growth rate and the frequency of dividing cells in this study. The resulting relationship was compared to ¹⁴C-bicarbonate derived growth rates. Productivity estimates using frequency of dividing cells correlated closely to sodium ¹⁴C-bicarbonate results and indicated a range of productivity by autotrophic picoplankton of 55.6% the total phytoplankton primary productivity in July to a January rate of 2.3%. Annual autotrophic picoplankton abundance varied seasonally in the lower Chesapeake Bay ranging from 7.26 × 10⁶ cells 1^–1 in winter to 9.28 × 10⁸ cells 1^–1 during late summer.