Individual feeding variability of protozoan and crustacean zooplankton analyzed with flow cytometry1

Abstract

Feeding of protozoan and crustacean zooplankton was analyzed by flow cytometry (FCM), resulting in direct counts of particles ingested by each individual. Ciliates ( Cyclidium sp.) were allowed to feed on Microcystis aeruginosa and analyzed directly on a flow cytometer for cyanobacterial autofluorescence coincident with each ciliate. Numbers of Microcystis cells ingested (e.g. 0, 1, 2, 3, or 4 ciliate −1 ) were estimated from the total fluorescence intensity of each ciliate. Crustaceans ( Daphnia magna and Bosmina tubicen ) were fed fluorescent beads or Microcystis , sonicated to release their gut contents, and the resulting suspension from each individual was quantitatively analyzed by FCM. These methods allow estimation of several aspects of feeding behavior, including particle selectivity, mechanisms of particle capture, gut volume of small organisms, feeding and clearance rates, and individual variation of the preceding parameters. Flow cytometry is more rapid than direct counts by microscope and more accurate than many indirect methods.