Grazing on bacteria by flagellates and cladocerans in lakes of contrasting food-web structure |
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Authors: | Vaque, Dolors Pace, Michael L. |
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Affiliation: | Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA |
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Abstract: | We tested the hypothesis that grazing on bacteria would varybetween lakes with differing plankton community structures.Paul and Tuesday lakes (Gogebic County, MI) are respectivelydominated by piscivorous and planktivorous fish. Consequently,zooplankton in Paul are primarily large daphnids, while zooplanktonin Tuesday are primarily small cladocerans and copepods. Wemeasured flagellate grazing on bacteria using a fluorescentminicell method, while cladoceran grazing was estimated fromthe relationship between body length and filtering rate. Wepredicted that cladoceran grazing on bacteria would be higherin Paul, and flagellate grazing would be higher in Tuesday.Cladoceran grazing on bacteria was important in both lakes contraryto our initial expectation. Large populations of the small cladoceran,Bosmina longirostris, in Tuesday exerted a grazing pressure(0.1835x106 bacteria 11 h1) approximatelyequal to that of the large cladoceran, Daphnia pulex, in Paul(0.3430x106 bacteria 11 h1). Flagellategrazing was higher in Tuesday as predicted (range: Paul, 0.16x106bacteria 11 h1; Tuesday, 0.220x106 bacteria11 h1). However, there was not a simple relationshipbetween total abundance of flagellates and total grazing rates.High community grazing by flagellates occurred when attachedchoanoflagellates were present. These flagellates had higheringestion rates than free forms. We find no clear evidence thatdifferences in food-web structure between the two lakes influencethe process of grazing on bacteria. Instead, our results emphasizethe significance of cladocerans and attached flagellates asconsumers of bacteria in freshwater ecosystems. |
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