Flow Cytometry is an important technique we use in our study of the predator-prey relationship between gelatinous grazers and ocean microorganisms. Flow cytometry detects and measures cell characteristics of the microbial prey consumed by gelatinous grazers. A flow cytometer instrument has three main components (fluidics, optics, and electronics) that work together to provide a complete system of cell analysis. We begin the process with a sample of phytoplankton cells taken from the gut of gelatinous grazers, suspended in a fluid, and injected into a flow cytometer. It takes measurements of the cells, one by one, as they pass by its laser at rates of many thousands of cells per second. Since the cells we have extracted have a natural fluorescence, the light is absorbed and then scattered in a band of wavelengths that is characteristic to the cells and their components. In this process, the instrument's optical system generates a photocurrent which is digitized. The data is then gathered and processed by a computer for our scientific analysis. 

Gelatinous Grazers and their microbial prey (phytoplankton) are the focus of our study. We seek to understand the impact gelatinous grazers (salps, appendicularians, doliolids, pyrosomes, and pteropods) and their high feeding rates have on microorganism populations in oceanic food webs. Using flow cytometry we can examine the microbe composition in the guts of gelatinous grazers and in the seawater samples to determine grazing rates, selectivity of prey, and mechanisms involved in infiltration and retention. We take advantage of the autofluorescence of phytoplankton to detect, count, differentiate, and sort them into groups based on their unique combinations of pigment and cell size. Flow cytometry provides an accurate, quantitative description of the microorganism community preyed upon by gelatinous grazers, and helps us understand their role in food web models.

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Graphic illustration of flow cytometry

Image courtesy of Dr. Kelly Sutherland