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JPR Advance Access originally published online on July 22, 2009
Journal of Plankton Research 2009 31(10):1235-1247; doi:10.1093/plankt/fbp060
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Toxin concentration in Nodularia spumigena is modulated by mesozooplankton grazers

Elena Gorokhova1 and Jonna Engström-Öst2,*

1 Department of Systems Ecology, Stockholm University, SE-10691 Stockholm, Sweden 2 ARONIA Coastal Zone Research Team, Åbo Akademi University and Novia University of Applied Sciences, Raseborgsvägen 9, FI-10600 Ekenäs, Finland

* CORRESPONDING AUTHOR: jonna.engstrom-ost{at}novia.fi

Received on April 30, 2009; accepted on June 28, 2009


  Abstract

The ecological role of nodularin in cyanobacterium Nodularia spumigena is still largely unknown, as are the conditions that promote toxin production. We report a modulating effect of mesozooplankton grazing on cellular nodularin content in N. spumigena expressed as a decrease in cell-bound toxin concentration in the presence of copepods compared with the cyanobacterium in similar assemblages without copepods. In our experiments, N. spumigena was incubated in an ambient plankton (<90 µm) assemblage (Expt I) or in 0.2-µm filtered seawater (Expt II), with and without the copepod Eurytemora affinis. Following ~28-h incubation, we measured the changes in N. spumigena abundance and nodularin concentration, frequency of Nodularia DNA occurrence in copepods as a proxy for grazing pressure on the cyanobacterium and individual RNA content in E. affinis as a proxy for copepod growth response. In all copepod-free treatments, intracellular nodularin concentrations were up to four times higher than in the treatments containing copepods. In Experiment I, the copepods also had a positive effect on the cyanobacterium growth, presumably due to a selective removal of more edible algal species and thus decreased competition for nutrients. Nodularia DNA was detected with high frequencies, 18–80%, increasing in treatments with no alternative food or high copepod densities. Simultaneously, no noxious effects of N. spumigena on the copepods were detected as indicated by higher RNA content in copepods exposed to N. spumigena with or without ambient plankton organisms compared with starved controls. These findings stress the need to understand the importance of intra-specific interactions for nodularin production in relation to population dynamics of N. spumigena.

Corresponding editor: Roger Harris


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