A method for in situ study of the effects of grazing on the species composition and standing crop of a natural phytoplankton assemblage is described. Polyethylene enclosures 0.5 m3 in volume are filled with whole lake water or water filtered through 125‐µ (No. 10) mesh to remove the major grazers. After 4 days of incubation, contents are sampled and cells counted by species. The bagged whole lake water is also compared with natural lake water. The total number of small algal cells (2–30 µ), small flagellates, large dinoflagellates, large chrysophytes, and ciliates are higher and gelatinous greens are lower in the absence of grazers. There is no detectable experimental effect on the total number of large cells (>30 µ), blue‐greens, desmids, small chrysophytes, diatoms, and nonbluegreen filaments.
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Karen G. Porter (1972) studied this question.