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Aquatic Microbial Ecology

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AME 52:69-82 (2008)  -  DOI:

Estimates of virus- vs. grazing induced mortality of picophytoplankton in the North Sea during summer

A. C. Baudoux1,2, M. J. W. Veldhuis1, A. A. M. Noordeloos1, G. van Noort1, C. P. D. Brussaard1,*

1Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, The Netherlands
2Present address: Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0202, USA
*Corresponding author. Email:

ABSTRACT: Microzooplankton grazing and virally mediated mortality of the eukaryotic (3 size classes) and prokaryotic (Synechococcus) picophytoplankton was investigated across the North Sea during summer 2003. The fate of picophytoplankton differed among algal groups and their area of occurrence. Highest viral lysis rates (0.16 to 0.23 d–1) were recorded for specific picoeukaryotic groups in the coastal region and at a station at the deep chlorophyll a maximum (DCM). Viral lysis was insignificant at the other stations, despite a considerable percentage of dead algal cells (up to 38%), as determined by staining with the live/dead dye SYTOX Green. Microzooplankton actively grazed on picoeukaryotes (average per group 0.2 to 0.4 d–1), independent of the region studied. Grazing on Synechococcus was restricted to the coastal waters (0.7 d–1). Grazing by microzooplankton consumed 40 ± 27% (mean ± SD) of the carbon produced by picophytoplankton, constituting in general the main loss factor. Viral lysis released 8 ± 13% of the total picophytoplankton carbon production, and locally up to 32%.

KEY WORDS: Viral lysis · Microzooplankton grazing · Phytoplankton mortality · Oligotrophic ecosystem · North Sea · Summer

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Cite this article as: Baudoux AC, Veldhuis MJW, Noordeloos AAM, van Noort G, Brussaard CPD (2008) Estimates of virus- vs. grazing induced mortality of picophytoplankton in the North Sea during summer. Aquat Microb Ecol 52:69-82.

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