AME 33:201-205 (2003)  -  doi:10.3354/ame033201

Heterotrophic nanoflagellates and increased essential fatty acids during Microcystis decay

Sangkyu Park1,5,*, Michael T. Brett2, Dörthe C. Müller-Navarra3, Sang-Cheon Shin4, Anne M. Liston1, Charles R. Goldman1

1Department of Environmental Science and Policy, University of California, 1 Shields Avenue, Davis, California 95616, USA
2Department of Civil and Environmental Engineering, University of Washington, Box 352700, 301 More Hall, Seattle, Washington 98195, USA
3Institut für Hydrobiologie und Fischereiwissenschaft, Abteilung Biologische Ozeanographie, Universität Hamburg, Olbersweg 24, 22767 Hamburg, Germany
4Geyongsangbuk-do Provincial Institute of Health and Environment, Deagu, 702-702, South Korea
5Present address: West Sea Fisheries Research Institute, San 66-3, Eulwang-dong, Jung-gu, Incheon 400-420, South Korea

ABSTRACT: To investigate the potential for heterotrophic organisms to upgrade the food quality of seston, we performed decay experiments using a non-toxic Microcystis aeruginosa (cyanobacteria) monoculture. The experiment was performed in darkness with aeration using a microbial inoculum collected from a hypereutrophic pond. Chlorophyll a concentrations decreased throughout the decay experiment. In contrast, eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3) concentrations increased and peaked on Day 5, while a-linolenic acid (a-LA, 18:3ω3) and stearidonic acid (18:4 ω3) gradually decreased, suggesting that EPA and DHA might be converted from a-LA and stearidonic acid. Microscopic examination revealed that a heterotrophic nanoflagellate (HNF) and the ciliate Vorticella sp. dominated the biological community during this experiment. Further examination using scanning electron microscopy (SEM) identified the HNF as Paraphysomonas vestita ssp. vestita, whose biovolume was very strongly correlated with EPA concentrations. Size-fractionized fatty acid determinations carried out on Day 6 showed that approximately two-thirds of the seston¹s total EPA content was in the <5 μm size fraction, which corresponded to the P. vestita size fraction. This size fraction also had a fatty acid content (relative to carbon content) 3 times higher than the 5 to 10 or >10 μm seston size fractions.

KEY WORDS: Trophic upgrading · Essential fatty acids · Food quality · Microcystis · Decaying · Paraphysomonas

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