  We introduce an image cytometer (I-CYT) for the analysis of phytoplankton in
fresh and marine water environments. A linear quantification of cell numbers
was observed covering several orders of magnitude using cultures of Tetraselmis
and Nannochloropsis measured by autofluorescence in a laboratory environment.
We assessed the functionality of the system outside the laboratory by
phytoplankton quantification of samples taken from a marine water environment
(Dutch Wadden Sea, The Netherlands) and a fresh water environment (Lake Ijssel,
The Netherlands). The I-CYT was also employed to study the effects of two
ballast water treatment systems (BWTS), based on chlorine electrolysis and UV
sterilization, with the analysis including the vitality of the phytoplankton.
For comparative study and benchmarking of the I-CYT, a standard flow cytometer
was used. Our results prove a limit of detection (LOD) of 10 cells/ml with an
accuracy between 0.7 and 0.5 log, and a correlation of 88.29% in quantification
and 96.21% in vitality, with respect to the flow cytometry results.
