A COMPARISON OF ESTIMATES OF PRODUCTIVITY AND CONSUMPTION BY ZOOPLANKTON FOR PLANKTONIC CILIATES IN LAKE-ONTARIO

A multiple regression equation predicting growth rate for ciliates from cell size and temperature was combined with measurements of biomass to estimate the productivity of ciliates in the epilimnion of Lake Ontario. This method predicts daily production to biomass values for ciliates of up to 5 day-1 and leads to the conclusion that ciliate production could equal half of the carbon fixation by phototrophs. Consumption of ciliates by metazoan zooplankton was estimated by incubating samples passed through 44-mu-m screens, and determining the increase in abundance of ciliates over 24 h. These rates are much lower, < 1 day-1 and often near zero. Production estimates based on these latter rates would be approximately 3-4% of primary production. Possible explanations for this discrepancy include both predation within the microzooplankton community and food limitation, as well as bottle effects. However, the lower production estimates are still compatible with ciliates playing a major role as grazers in this ecosystem.