Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 11, issue 23
Biogeosciences, 11, 6739–6753, 2014
https://doi.org/10.5194/bg-11-6739-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: KEOPS2: Kerguelen Ocean and Plateau Study 2

Biogeosciences, 11, 6739–6753, 2014
https://doi.org/10.5194/bg-11-6739-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 05 Dec 2014

Research article | 05 Dec 2014

Microbial food web dynamics during spring phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean)

U. Christaki1, D. Lefèvre2, C. Georges1, J. Colombet3, P. Catala4,5, C. Courties6,7, T. Sime-Ngando3, S. Blain4,5, and I. Obernosterer4,5 U. Christaki et al.
  • 1INSU-CNRS, UMR8187 LOG, Laboratoire d'Océanologie et des Géosciences, Université du Littoral Côte d'Opale, ULCO, 32 avenue Foch, 62930 Wimereux, France
  • 2Aix Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO), UM110, 13288 Marseille, France
  • 3INEE-CNRS, UMR6023, LMGE, Laboratoire Microorganismes: Génome et Environnement – Clermont Université, Université Blaise Pascal, 63177 Aubière CEDEX, France
  • 4CNRS, UMR7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls-sur-mer, France
  • 5Sorbonne Universités, UPMC Univ Paris 06, UMR7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls-sur-mer, France
  • 6CNRS, UMS2348, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, Banyuls-sur-mer, France
  • 7Sorbonne Universités, UPMC Univ Paris 06, UMS2348, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls-sur-mer, France

Abstract. Microbial food web dynamics were determined during the onset of several spring phytoplankton blooms induced by natural iron fertilization off Kerguelen Island in the Southern Ocean (KEOPS2). The abundances of heterotrophic bacteria and heterotrophic nanoflagellates, bacterial heterotrophic production, bacterial respiration, and bacterial growth efficiency, were consistently higher in surface waters of the iron-fertilized sites than at the reference site in HNLC (high nutrient low chlorophyll) waters. The abundance of virus-like particles remained unchanged, but viral production increased by a factor of 6 in iron-fertilized waters. Bacterial heterotrophic production was significantly related to heterotrophic nanoflagellate abundance and viral production across all sites, with bacterial production explaining about 70 and 85%, respectively, of the variance of each in the mixed layer (ML). Estimated rates of grazing and viral lysis, however, indicated that heterotrophic nanoflagellates accounted for a substantially higher loss of bacterial production (50%) than viruses (11%). Combining these results with rates of primary production and export determined for the study area, a budget for the flow of carbon through the microbial food web and higher trophic levels during the early (KEOPS2) and the late phase (KEOPS1) of the Kerguelen bloom is provided.

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The concurrent investigation of several parameters has provided insight into two key roles of heterotrophic bacteria, and the microbial food web functioning, at the onset and late phase of the spring phytoplankton bloom induced by natural iron fertilization in the Southern Ocean.
The concurrent investigation of several parameters has provided insight into two key roles of...
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