Flow Cytometry is an advanced method of counting individual cells, and assigning them to general categories. The technology used today in ocean research evolved from technology developed in the 1970s to count blood cells. It can rapidly measure small differences in size and pigments in individual cells as they pass through a laser beam. These variations are enough to identify different types of plankton, including very small microbes, quickly and accurately. While a scientist might be able to count a few hundred cells in a minute, a Flow Cytometer can not only count, but also identify many thousands of cells in the same time. Two different instruments that employ Flow Cytometer technology presently being used by the Census are the Flow Cytobot and the Environmental Sample Processor (ESP). Both enable scientists to study plankton community structure and dynamics in great detail and create image catalogs for further analysis and identification.
The Flow Cytobot  being lowered off the side of the coastal research vessel MYTILUS. This instrument allows work that is usually done in a laboratory to be done by scientists in the field. (Tom Kleindinst, Woods Hole Oceanographic Institution)
A diagram of the Environmental Sample Processor (ESP),  another instrument that works similarly to a standard Flow Cytometer. The ESP can be used to gather several different pieces of information, such as the genetic composition of microbial organisms in the ocean, and is now being used by Census projects. (Image courtesy Monterey Bay Aquarium Research Institute and ICoMM)