Aquatic Ecology

, Volume 40, Issue 3, pp 299–313 | Cite as

Changes in the pelagic microbial food web due to artificial eutrophication

  • Agneta AnderssonEmail author
  • Kristina Samuelsson
  • Pia Haecky
  • Jan Albertsson
Original Paper


The effect of nutrient enrichment on the structure and carbon flow in the pelagic microbial food web was studied in mesocosm experiments using seawater from the northern Baltic Sea. The experiments included food webs of at least four trophic levels; (1) phytoplankton–bacteria, (2) flagellates, (3) ciliates and (4) mesozooplankton. In the enriched treatments high autotrophic growth rates were observed, followed by increased heterotrophic production. The largest growth increase was due to heterotrophic bacteria, indicating that the heterotrophic microbial food web was promoted. This was further supported by increased growth of heterotrophic flagellates and ciliates in the high nutrient treatments. The phytoplankton peak in the middle of the experiments was mainly due to an autotrophic nanoflagellate, Pyramimonas sp. At the end of the experiment, the proportion of heterotrophic organisms was higher in the nutrient enriched than in the nutrient-poor treatment, indicating increased predation control of primary producers. The proportion of potentially mixotrophic plankton, prymnesiophyceans, chrysophyceans and dinophyceans, were significantly higher in the nutrient-poor treatment. Furthermore, the results indicated that the food web efficiency, defined as mesozooplankton production per basal production (primary production + bacterial production − sedimentation), decreased with increasing nutrient status, possibly due to increasing loss processes in the food web. This could be explained by promotion of the heterotrophic microbial food web, causing more trophic levels and respiration steps in the food web.


Bacteria Food web structure Mesocosm experiments Mesozooplankton Phytoplankton Protozoa 


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This study was financed by the Eucon project, Swedish Environmental Protection Agency. We thank Rocio Quadros-Hansson and Birgitta Karlsson for technical assistance. The use of data collected in the national Swedish marine monitoring programme is gratefully acknowledged. We thank the marine chemistry group at Umeå Marine Sciences Centre for chemical analyses.


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Copyright information

© Springer Science+Business Media B.V. 2006

Authors and Affiliations

  • Agneta Andersson
    • 1
    • 2
    Email author
  • Kristina Samuelsson
    • 1
    • 2
    • 3
  • Pia Haecky
    • 2
    • 4
  • Jan Albertsson
    • 2
  1. 1.Marine Ecology, Department of Ecology and Environmental ScienceUmeå UniversityUmeåSweden
  2. 2.Umeå Marine Sciences CentreHörneforsSweden
  3. 3.Division of Medical Microbiology, Department of Molecular and Clinical MedicineLinköping UniversityLinköpingSweden
  4. 4.Botanical InstituteUniversity of CopenhagenCopenhagen KDenmark

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