Microbial Ecology

, Volume 53, Issue 1, pp 134–142 | Cite as

Ciliates are the Dominant Grazers on Pico- and Nanoplankton in a Shallow, Naturally Highly Eutrophic Lake

  • Priit Zingel
  • Helen Agasild
  • Tiina Nõges
  • Veljo Kisand
Article

Abstract

Abundance and biomass of the microbial loop members [bacteria, heterotrophic nanoflagellates (HNF), and ciliates] were seasonally measured in the naturally eutrophic and shallow (2.8 mean depth) Lake Võrtsjärv, which has a large open surface area (average 270 km2) and highly turbid water (Secchi depth <1 m). Grazing rates (filter feeding rates) on 0.5-, 3-, and 6-μm-diameter particles were measured to estimate pico- and nanoplankton grazing (filter feeding) by micro- and metazooplankton. Among grazers, HNF had a low abundance (<50 cells mL−1) and, due to their low specific filtering rates, they only grazed a minor fraction of the bacterioplankton (≤4.2% of total grazing). Ciliates were relatively abundant (≤158 cells mL−1) and, considering their high specific feeding rates, were able to graze more than 100% of the bacterial biomass production in the open part of the lake, whereas the average daily grazing accounted for 9.3% of the bacterial standing stock. Ciliates were potentially important grazers of nanoplanktonic organisms (on average, approximately 20% of the standing stock of 3-μm-size particles was grazed daily). Metazooplankton grazed a minor part of the bacterioplankton, accounting for only 0.1% of standing stock of bacteria. Grazing on nanoplankton (3–6 μm) by metazooplankton was higher (0.4% of standing stock). The hypothesis is proposed that ciliates dominate due to a lack of top–down regulation by predators, and HNF have a low abundance due to strong grazing pressure by ciliates.

Notes

Acknowledgments

We are grateful to Dr. Mark Dopson who made valuable language revision on the manuscript. This study was funded by grants to Tiina Nõges from the Estonian Ministry of Education (0362480s03) and by Estonian Science Foundation grants 4080 and 5738, and to Veljo Kisand from the Hanse Advanced Institute and EU Marie Curie MERG-CT-6-2005-014873. Data collection in state monitoring program was supported by Estonian Ministry of Environment.

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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Priit Zingel
    • 1
    • 2
  • Helen Agasild
    • 1
  • Tiina Nõges
    • 1
  • Veljo Kisand
    • 1
    • 3
  1. 1.Institute of Agricultural and Environmental Sciences, Võrtsjärv Centre for LimnologyEstonian University of Life SciencesRannuEstonia
  2. 2.Institute of Veterinary Medicine and Animal SciencesEstonian University of Life SciencesTartuEstonia
  3. 3.Institute of TechnologyUniversity of TartuTartuEstonia

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