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

• Priit Zingel ^{[3] [1]} ; Helen Agasild ^[3] ; Tiina Nõges ^[3] ; Veljo Kisand ^{[3] [2]}
  1. [1] Estonian University of Life Sciences

     Estonian University of Life Sciences

     Tartu linn, Estonia

     
  2. [2] University of Tartu

     University of Tartu

     Tartu linn, Estonia

     
  3. [3] Institute of Agricultural and Environmental Sciences, Võrtsjärv Centre for Limnology, Estonian University of Life Sciences. Tartu County, Estonia

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• Localización: Microbial ecology, ISSN-e 1432-184X, ISSN 0095-3628, Vol. 53, Nº. 1, 2007, págs. 134-142
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • 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.