Seasonal and Vertical Distribution of Ciliophora in Lake Ontario

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Abstract
Ciliated protozoa were sampled at discrete depths from April through October 1982 at a nearshore (38 m depth) and an offshore (178 m depth) station in Lake Ontario. Nearshore, ciliates increased from less than 1 g∙m−2 in early spring to a maximum of about 5 g∙m−2 (wet weight) inside the thermal bar in late May and early June. Summer values varied around 2 g∙m−2 and declined even further in October. Offshore ciliate biomass was relatively constant; the observed range was only 2.8–6.5 g∙m−2. Early spring biomass was much higher than nearshore, suggesting that a significant population persists through the winter, but the spring biomass increase was later. Although biomass concentration was greater in the epilimnion, on an areal basis most of the population resided in the hypolimnion. The hypolimnetic population declined during the summer period of thermal stratification. The observed number of taxa ranged from 15 to 30 per sample. Most had distinct seasonal and vertical distributions. The majority appear to be algivores, but the role of ciliates in the food web of Lake Ontario remains largely unknown. Their biomass is comparable with that of metazoan zooplankton, and with their higher metabolic rates, they probably perform much more of the total grazing.

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