Marine Biology

, Volume 146, Issue 3, pp 531–541 | Cite as

Impacts of copepods on marine seston, and resulting effects on Calanus finmarchicus RNA:DNA ratios in mesocosm experiments

  • C. Becker
  • D. Brepohl
  • H. Feuchtmayr
  • E. Zöllner
  • F. Sommer
  • C. Clemmesen
  • U. Sommer
  • M. Boersma
Research Article


We investigated the impact of copepods on the seston community in a mesocosm set-up, and assessed how the changes in food quantity, quality and size affected the condition of the grazers, by measuring the RNA:DNA ratios in different developmental stages of Calanus finmarchicus. Manipulated copepod densities did not affect the particulate carbon concentration in the mesocosms. On the other hand, chlorophyll a content increased with higher copepod densities, and increasing densities had a positive effect on seston food quality in the mesocosms, measured as C:N ratios and ω3:ω6 fatty acid ratios. These food quality indicators were significantly correlated to the nutritional status of C. finmarchicus. In contrast to our expectations, these results suggest a lower copepod growth potential on higher quality food. However, in concordance with earlier studies, we found that when copepods were in high densities the large particles (>1000 µm3) decreased and that the smaller particles (<1000 µm3) increased in number. These patterns were closely linked to the condition of C. finmarchicus, which were of better condition (RNA:DNA ratios) with increasing biovolumes of large particles, and, conversely, lower RNA:DNA ratios with increasing biovolumes of smaller particles. Consequentially, the selective grazing by copepods stimulated increased biovolumes of smaller plankton, and this increase was responsible for the increased food quality, in terms of C:N and ω3:ω6 ratios. Thus, we conclude that the decreasing growth potentials of C. finmarchicus were a result of a decrease of favourably sized food particles, induced by copepod grazing.


Food Treatment Plankton Community Mesocosm Experiment Food Quantity Copepodite Stage 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This work would not have been possible without the IfM-MPIL food web team. We thank the European Commission’s programme (Improving Human Potential—Access to Research infrastructure) for the access to Trondheim Marine Systems Research Infrastructure in Hopavågen, Sletvik, Norway. Ø. Leiknes and A. Neyts are especially acknowledged for their valuable help during our stay in Norway. W. DeMott provided interesting discussions and constructive criticism on earlier drafts of this manuscript. This research was partly supported by DFG-grants: BO1488/3-1, SA 638/1-1, SO145/19-1, JU367/4-1 and CNPq (Brazil).


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • C. Becker
    • 1
    • 4
  • D. Brepohl
    • 2
  • H. Feuchtmayr
    • 1
  • E. Zöllner
    • 1
  • F. Sommer
    • 2
  • C. Clemmesen
    • 2
  • U. Sommer
    • 2
  • M. Boersma
    • 3
  1. 1.Max-Planck-Institut für LimnologiePlönGermany
  2. 2.Leibniz-Institut für MeereswissenschaftenIFM-GEOMAR Marine ÖkologieKielGermany
  3. 3.Alfred-Wegener-Institut für Polar und MeeresforschungBiologische Anstalt HelgolandHelgolandGermany
  4. 4.WK Kellogg Biological StationMichigan State UniversityUSA

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