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AME 33:191-199 (2003)
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Abstract
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Grazing by Prymnesium parvum on small planktonic diatoms
Mercedes Martin-Cereceda1,*, Gianfranco Novarino1, Jeremy R. Young2
1Department of Zoology, and
2Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
*Email: merm@nhm.ac.uk
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ABSTRACT: This is the first qualitative and quantitative evidence showing that the marine mixotrophic flagellate Prymnesium parvum (Prymnesiida = Prymnesiophyceae p.p.) is able to graze on small (5 µm) planktonic diatoms of the genera
Minidiscus and Thalassiosira. Flagellate grazing and diatom species preferences were determined quantitatively in monoxenic batch cultures under nutrient depletion. Video microscopy coupled with digital film was used to visualise the
ingestion process. Prey-switching was also investigated using bacteria as an alternative prey and the results were compared with flagellate growth dynamics in the absence of any prey. P. parvum started to graze on diatom cells about 5 min after the
diatoms were introduced into the flagellate culture flasks. A reduction of about two-thirds of the initial diatom population occurred in both diatom taxa during the first 2 h of contact in flasks without bacteria. High interim grazing rates occurred
during the first 8 h (0.30 diatom flagellate-1 h-1 for M. trioculatus and 0.74 diatom flagellate-1 h-1 for Thalassiosira sp.); when bacteria were added, prey-switching (from diatom cells to
bacteria) was observed in the M. trioculatus experiment. Grazing rates on both diatom species for the duration of the experiment (144 h) were not statistically different (0.017 diatom flagellate-1 h-1); when bacteria were
added these rates decreased (0.003 diatom flagellate-1 h-1 for Minidiscus trioculatus and 0.002 diatom flagellate-1 h-1 for Thalassiosira sp.). Bacterial grazing by P. parvum was also
similar in both diatom flasks (0.17 bacteria flagellate-1 h-1). Addition of diatoms to the cultures did not enhance flagellate growth. Diatom capture usually involved the production of a pseudopodium-like structure at the posterior
end of flagellate cells. Overall, these results suggest that predation by mixotrophic prymnesiophyte flagellates may be an important factor in regulating populations of nanoplanktonic diatoms in marine environments.
KEY WORDS: Diatom grazing · Bacterivory · Marine nanoplankton · Mixotrophic flagellates · Nutrient limitation · Prymnesium parvum
Full text in pdf format
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Published in AME Vol.
33, No. 2
(2003) on October 14
Print ISSN: 0948-3055; Online ISSN: 1616-1564.
Copyright © Inter-Research, Oldendorf/Luhe, 2003
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