ABSTRACT
Rates of grazing on bacteria or phytoplankton by protists in natural waters may be estimated by evaluating the average rate of particle ingestion by specific components of the protistan assemblage in a water sample, for example, flagellates, ciliates, identified morphological types, or size fractions. The usual experimental design for this method is one in which short-term, cell-specific uptake rates are determined via quantifying the average number of prey particles within protistan cells over a time course ranging from 10 to 60 minutes. Advantages of the method are: grazing rates are determined via short time-course experiments, minimizing the potential problems associated with long time-course experiments and there is minimum manipulation of the sample, no size screening, dilution, or addition of chemicals is necessary. It also includes the specific components of the protistan assemblage which are the most active consumers of the type of fluorescently labelled prey used are directly identified.
