35 The potential magnitude of grazing pressure on
freshwater phytoplankton has only recently been
determined empirically. Studies by Hargrave and
Geen estimated natural community grazing rates by
measuring feeding rates of individual zooplankton
40 species in the laboratory and then computing com-
munity grazing rates for field conditions using the
known population density of grazers. The high esti-
mates of grazing pressure postulated by these
researchers were not fully accepted, however, until the
45 grazing rates of zooplankton were determined directly
in the field, by means of new experimental techniques.
Using a specially prepared feeding chamber, Haney
was able to record zooplankton grazing rates in natural
field conditions. In the periods of peak zooplankton
50 abundance, that is, in the late spring and in the summer,
Haney recorded maximum daily community grazing rates,
for nutrient-poor lakes and bog lakes, respectively, of 6.6
percent and 114 percent of daily phytoplankton production.
Cladocerans had higher grazing rates than
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