The application of flow cytometry to the monitoring of phytoplankton i
s demonstrated. A comparison is made with conventional approaches to p
hytoplankton monitoring: light microscopy for the determination of spe
cies abundance, and chlorophyll a determination and in situ chlorophyl
l a measurement by fluorescence for the determination of the biomass.
Flow cytometric measurements correlate well with these conventional ty
pes of measurements, as has been shown by comparing a full year of mon
itoring data obtained at a fixed monitoring location 10 km off the Dut
ch coast. Flow cytometry bridges the gap between labour-intensive, but
highly informative, microscopic observations and simple biomass measu
rements with less information content: via flow cytometry optical data
are obtained at high speed for individual particles, which can be tra
nslated into biomass information. On the basis of the flow cytometric
measurements, rough discrimination of phytoplankton species groups is
possible, particularly for the abundant species. Of crucial importance
is careful calibration of the flow cytometer, to ensure quantitative
and comparable measurements over a long period of time. Calibration an
d quality assurance aspects are covered in detail.