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Microzooplankton grazing and phytoplankton growth in marine mesocosms with increased CO2 levels
1Leibniz Institute for Marine Sciences (IFM-GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany
2University of Bergen, Department of Biology, P.O. Box 7800, 5020 Bergen, Norway
3Department of Biology, UNIFOB, P.O. Box 7800, 5020 Bergen, Norway
4Facultad de Ciencias del Mar, Universidad de las Palmas de Gran Canaria, 35017 Tafira Baja – Las Palmas, Spain
5Stazione Zoologica "A. Dohrn", Villa Comunale 1, 80121 Naples, Italy
6CAU Kiel, Institute for Physiology, Hermann-Rodewald-Straße 5, 24118 Kiel, Germany
Abstract. Microzooplankton grazing and algae growth responses to increasing pCO2 levels (350, 700 and 1050 μatm) were investigated in nitrate and phosphate fertilized mesocosms during the PeECE III experiment 2005. Grazing and growth rates were estimated by the dilution technique combined with taxon specific HPLC pigment analysis. Phytoplankton and microzooplankton composition were determined by light microscopy. Despite a range up to 3 times the present CO2 levels, there were no clear differences in any measured parameter between the different CO2 treatments. Thus, during the first 9 days of the experiment the algae community standing stock (SS), measured as chlorophyll a (Chl a), showed the highest instantaneous grow rates (0.02–0.99 d-1) and increased from ca 2–3 to 6–12 μg l−1, in all mesocosms. Afterwards the phytoplankton SS decreased in all mesocosms until the end of the experiment. The microzooplankton SS, that was mainly dinoflagellates and ciliates varied between 23 and 130 μg C l−1, peaking on day 13–15, apparently responding to the phytoplankton development. Instantaneous Chl a growth rates were generally higher than the grazing rates, indicating only a limited overall effect of microzooplankton grazing on the most dominant phytoplankton. Diatoms and prymnesiophytes were significantly grazed (14–43% of the SS d-1) only in the pre-bloom phase when they were in low numbers and in the post-bloom phase when they were already limited by low nutrients and/or virus lysis. The cyanobacteria populations appeared more effected by microzooplankton grazing, generally removing 20–65% of the SS d−1.
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Citation: Suffrian, K., Simonelli, P., Nejstgaard, J. C., Putzeys, S., Carotenuto, Y., and Antia, A. N.: Microzooplankton grazing and phytoplankton growth in marine mesocosms with increased CO2 levels, Biogeosciences Discuss., 5, 411-433, 2008. Bibtex EndNote Reference Manager
