Distribution of Planktonic Ciliates in Highly Coloured Subtropical Lakes: Comparison with Clearwater Ciliate Communities and the Contribution of Myxotrophic Taxa to Total Autotrophic Biomass

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SUMMARY 1. The planktonic ciliate communities of eleven organically coloured north and central Florida lakes representing a variety of trophic conditions were examined during 1979–80. The total abundance and biomass of ciliates were not significantly different from comparable clearwater lakes and only minor taxonomic replacements were noted at the order level.

2. Timing of population peaks of oligotrophic lakes was dissimilar to clearwater lakes of the same trophic state, but seasonality in meso‐trophic and eutrophic lakes resembled patterns described for comparable clearwater lakes.

3. Various ciliate components were strongly correlated with chlorophyll a concentrations, but only moderately correlated to dominant phytoplankton groups. No significant correlations were found between ciliate components and bacterial abundance. 4. Myxotrophic taxa numerically dominated oligotrophic systems, particularly during midsummer, and accounted for a large percentage of the total ciliate biomass. Estimates of the ciliate contribution to total autotrophic biomass indicate that these zoochlorellae‐bearing protozoa may account for much of the autotrophic biomass during midsummer periods in coloured lakes, and thus may lead to an overestimation of phytoplankton standing crops available to zooplankton grazers if chlorophyll a is used as a surrogate measure of algal biomass.

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Freshwater Biology, v. 20, issue 1, p. 51-60