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Aquatic Microbial Ecology

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AME 45:79-87 (2006)  -  doi:10.3354/ame045079

Mixotrophic nanoflagellates in coastal sediments in the western Baltic Sea

Stefanie Moorthi1,2,*, Ulrike-G. Berninger1,3

1Leibniz Institute of Marine Sciences at Kiel University (IFM-GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany
2Present address: University of Southern California, Department of Biological Sciences, 3616 Trousdale Parkway, AHF 301, Los Angeles, California 90089-0371, USA
3Present address: University of Salzburg, Department of Organismic Biology, Hellbrunner Str. 34, 5020 Salzburg, Austria

ABSTRACT: Benthic mixotrophic nanoflagellates (MNF) were studied in coastal sediments in Kiel Fjord, western Baltic Sea. Three types of surface sediment of different grain size were investigated, each along a vertical gradient within the first centimeter depth. A tracer experiment using fluorescently labeled bacteria (FLB) was conducted to identify MNF and quantify their contribution to total bacterivory in different sediment types and depths. MNF abundances and their phagotrophic activity did not vary significantly with sediment depth and grain size. Overall, mixotrophs contributed less to total nanoflagellates in sediments from Kiel Fjord (max. 2%) than those recorded from comparable pelagic systems, contributing a higher percentage to total phytoflagellates than to the total bacterivores (5 to 10 vs. 2 to 5%, respectively). Potential reasons for these findings could be extensive niche segregation for bacterial grazers, osmotrophic feeding strategies in sediments due to high bacterial abundances and/or rarely limiting nutrient conditions.

KEY WORDS: Mixotrophy · Mixotrophic nanoflagellates · Coastal sediment · Benthic microbial ecology · Benthic protists

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