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SEPG 2051 - Date Awarded 2002

Mixotrophy: An important survival strategy in extreme lacustrine ecosystems?

Dr. Elanor M. Bell

Abstract

Grazing by phototrophic nanoflagellates (PNAN) in naturally acidic Colour Lake on Axel Heiberg Island, Nunavut, Canadian High Arctic was investigated in spring 2000 and summer 2002. Three dominant PNAN were identified: a Chlamydomonad, Ochromonas sp. and Cryptomonas sp. The latter did not graze, but the Chlamydomonad and Ochromonas sp. did. The maximum ingestion rates of these two species were 0.467 and 0.089 FLP cell-1 h-1, respectively, at a depth of 20 m in the lake. The PNAN community only removed 0.1 to 1.3 % of the in situ bacterial population, equivalent to between 0 and 14% of in situ bacterial production. It was estimated that neither the Chlamydomonads nor Ochromonas sp. derived more than 1 % of their daily cell carbon requirements from bacterivory, neither in spring 2000 nor summer 2002. This study confirms that the dominant PNAN species in Colour Lake are mixotrophic and suggests that mixotrophy is a strategy by which the PNAN community could survive the Arctic winter.

Full report: SEPG2051

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