Composition and speciation in salt water columns is of key importance to understanding the complex interaction of marine environments. Enumerating and classifying planktonic cells can be a good indicator of primary production, water quality, and overall species diversity. Because these marine organisms are in suspension and exhibit diverse morphology, Amnis imaging flow cytometry is ideally suited for quantifying populations of diatoms, measuring algal cell division, and studying the diverse array of planktonic life forms.