Relative feeding rates on free and particle‐bound bacteria by freshwater macrozooplankton1

Abstract

Feeding suspensions of equivalent particle spectra were assembled with either free‐living (< 1.0 µ m) or attached bacteria specifically labeled with [ 3 H]thymidine. Clearance (ml ind −1 d −1 ) of attached bacteria was 3–29 × that of free bacteria for the cladocerans Acantholeberis, Chydorus, and Eubosmina. Pseudosida and Ceriodaphnia showed weaker discrimination or no selection, indicating a lower size threshold for filtration in these species. Feeding suspensions composed of isolated free bacteria yielded significantly higher or lower estimates of grazing than free bacteria with the full complement of particles, depending on species. Relative clearance (attached : free) tended to increase with body size within a species and varied for different particle environments. Bacteria associated with large particles may increase detrital energy flow to consumers in eutrophic environments.