Author(s): McManus GB, Fuhrman JA
fluorescent pigments were used to study the uptake of bacteria-sized particles by laboratory and field populations of heterotrophic nanoplankton. With membrane filtration these particles can be made to mimic the natural bac- terioplankton size distribution. Uptake was roughly linear for 20-40 min, and leveled off after that, with the number of particles per cell re- maining constant for at least several hours. Pho- tosynthetic nanoplankton did not take up the par- ticles in significant numbers. Experiments with a small nonpigmented flagellate indicated some se- lection against the particles in favor of ingestion of unicellular cyanobacteria, but this may have been based on the size of the particles rather than quality. Preliminary field experiments indicated that nonpigmented nanoplankton was responsi- ble for virtually all of the grazing on bacterio- plankton, with microzooplankton playing a mi- nor role.