Yentsch is known for adapting the use of
flow cytometry from biomedical research to the study of phytoplankton in marine systems. In 1981, Yentsch first demonstrated this by utilizing a flow cytometer from the medical laboratories of the
University of Rochester to quantify the amount of
saxitoxin in the red tide
dinoflagellate Gonyaulax. In 1982, Yentsch lead a team of scientists in the flow cytometric analysis of seawater samples collected at the Bermuda Biological Station (now the
Bermuda Atlantic Time-series Study) where they demonstrated 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. To develop this technology, Clarice Yentsch received funding in 1982 from the
National Science Foundation (OCE 8213567 for "Flow cytometry development for ocean science research" and OCE-8121331 "Carbon in autotrophs and heterotrophs separated by fluorescence-activated cell sorting"). In 1983, Clarice Yentsch established the Center for Aquatic Cytometry at Bigelow Laboratory for Ocean Sciences which is active to this day. In 1988,
Sallie W. Chisholm, Robert Olsen, and Clarice Yentsch described flow cytometry with the goal of introducing the technique to the oceanographic community, including a list of flow cytometers dedicated to oceanography and limnology. By 1984, the study of phytoplankton was advancing due to the ability of flow cytometry to characterize phytoplankton on small scales, as described in a paper led by Clarice Yentsch. By adding stains that bind to DNA, Yentsch and colleagues were able to quantify the
nucleic acid content of dinoflagellates and thereby estimate the actively-growing proportion of the microbial population. The use of flow cytometry in aquatic science advanced rapidly and in 1989 Clarice Yentsch and Paul Horan co-edited a special issue on "Cytometry in the Aquatic Sciences". At the same time, large scale investigations into phytoplankton ecology using satellites were beginning and Clarice and Charles Yentsch examined both of these tools in a 1984 publication. Clarice and Charlie had history of joint publications starting with two publications in 1970 on the quantification of phytoplankton pigments in oligotrophic oceans and the decomposition of
chlorophyll from marine phytoplankton. This early research was funded by a $31,900 grant from the
National Institutes of Health to Clarice Yentsch at the Northeastern Research Foundation, the precursor to Bigelow Laboratory for Ocean Sciences, for a project entitled "Assessment of health hazards from toxic red tide cysts". == Philanthropic activities ==