Seawater is collected and preserved to be analyzed in lab using an InFlux Flow Cytometer with the Spigot software package. The populations targeted for enumeration are Prochlorococcus, Synechococcus, unclassied pico-eukaryotes (cells sized around 1\u03bcm), and heterotrophic non-fluorescing bacteria. Each sample is divided in two, with one aliquot analyzed for autofluorescence and the other for heterotrophic bacteria stained with SYBR Green I. In both cases, excitation is produced using stacked 488nm and 457nm lasers. The data is analyzed using FlowJo (v10) to determine cell concentrations (cells\/mL).