Flow cytometry
In aquatic systems, flow cytometry is used for the analysis of autofluorescing cells or cells that are fluorescently-labeled with added stains. This research started in 1981 when Clarice Yentsch used flow cytometry to measure the fluorescence in a red tide producing dinoflagellate. The next year researchers published flow cytometric measurements of multiple algal species which could be distinguished based on their fluorescence characteristics. By 1983, marine researchers were assembling their own flow cytometers or using commercially available flow cytometers on seawater samples collected off Bermuda to demonstrate that phytoplankton cells could be distinguished from non-living material and that cyanobacteria could be sorted from a mixed community and subsequently cultured in the lab. Flow cytometry also allowed marine researchers to distinguish between dimly-fluorescing "Prochlorococcus" and heterotrophic microorganisms, a distinction that is difficult with microscopy-based assessments. Advances in technology now allow aquatic scientists to use flow cytometers continuously during research cruises and flow cytometers are used to provide images of individual phytoplankton cells. Marine scientists use the sorting ability of flow cytometers to make discrete measurements of cellular activity and diversity, to conduct investigations into the mutualistic relationships between microorganisms that live in close proximity, and to measure biogeochemical rates of multiple processes in the ocean.