Science Serving Maryland's Coasts

Miranda (Hoover) Kerr, Wittenberg University

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Flow Cytometric Indicators of Phytoplankton in the Chesapeake Bay.


We investigated the effectiveness of using flow cytometry parameters of light scatter and fluorescence as a means of measuring phytoplankton carbon per cell, chlorophyll per cell, cell volume, and cell abundance to monitor growth. As primary producers, phytoplankton are an important indicator of Chesapeake Bay ecosystem health. Common methods of monitoring phytoplankton do not take into account chlorophyll-to-carbon (ChlC) ratios or phytoplankton size spectra. We first considered the effects of mismatched sheath fluid and sample salinity on light scatter. We determined that matching sheath fluid to sample salinity gives the same forward light scatter (FLS) and side light scatter (SLS) values as using 0 salinity sample and sheath. Using 13 cultures, ranging in size from 1-30 m, we were able to produce a calibration curve for SLS to C/cell. Among our cultures, C/cell varied from 0.1 to 3600 pg/cell. The difference between the predicted and observed C/cell varied from 4 to 116% with an average of 41% and a median of 35%. This allowed us to create size spectra for our samples from the ACE-InC cruises of the Choptank and Patuxent Rivers. Size spectra data revealed the trend of larger cells tending towards the mid-river station and smaller cells tending towards the upper and lower stations in the river. This case study demonstrates that FCM parameters can provide complimentary information to chl a-biomass measurements and improve our ability to monitor phytoplankton as an indicator of Chesapeake Bay health.