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Biogeosciences, 8, 525-538, 2011
www.biogeosciences.net/8/525/2011/
doi:10.5194/bg-8-525-2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
Lack of P-limitation of phytoplankton and heterotrophic prokaryotes in surface waters of three anticyclonic eddies in the stratified Mediterranean Sea
T. Tanaka1, T. F. Thingstad2, U. Christaki3, J. Colombet4, V. Cornet-Barthaux1, C. Courties5,6, J.-D. Grattepanche3, A. Lagaria3,7, J. Nedoma8, L. Oriol9,10, S. Psarra7, M. Pujo-Pay9,10, and F. Van Wambeke11
1Université de la Méditerranée, CNRS, Laboratoire d'Océanographie Physique et Biogéochimique-UMR 6535, OSU/Centre d'Océanologie de Marseille, Campus de Luminy-Case 901, 13288 Marseille cedex 09, France
2Department of Biology, University of Bergen, Thormøhlens gate 55, 5006 Bergen, Norway
3Université Lille Nord de France, ULCO, LOG, CNRS, UMR 8187, 32 Avenue Foch, 62930 Wimereux, France
4Université Blaise Pascal (Clermont-Ferrand II), Laboratoire Microorganismes, Génome et Environnement, UMR CNRS 6023, 63177 Aubière cedex, France
5Université Pierre et Marie Curie-Paris 6, UMS 2348, Observatoire Océanologique, 66651 Banyuls sur mer, France
6CNRS, UMS 2348, Observatoire Océanologique, 66651 Banyuls sur mer, France
7Hellenic Centre for Marine Research, Institute of Oceanography, 71003 Heraklion, Crete, Greece
8Biology Centre ASCR, v.v.i., Institute of Hydrobiology, 37005 Ceske Budejovice, Czech Republic
9Université Pierre et Marie Curie-Paris 6, UMR 7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66651 Banyuls sur mer, France
10CNRS, UMR 7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66651 Banyuls sur mer, France
11Université de la Méditerranée, CNRS, Laboratoire de Microbiologie, Géochimie et Ecologie Marines-UMR 6117, OSU/Centre d'Océanologie de Marseille, Campus de Luminy-Case 901, 13288 Marseille, France

Abstract. We investigated the identity of the limiting nutrient of the pelagic microbial food web in the Mediterranean Sea using nutrient manipulated microcosms during summer 2008. Experiments were carried out with surface waters at the center of anticyclonic eddies in the Western Basin, the Ionian Basin, and the Levantine Basin. In situ, the ratio of N to P was always higher in both dissolved and particulate organic fractions compared to the Redfield ratio, suggesting a relative P-starvation. In each experiment, four different treatments in triplicates (addition of ammonium, phosphate, a combination of both, and the unamended control) were employed and chemical and biological parameters monitored throughout a 3–4 day incubation. Temporal changes of turnover time of phosphate and ATP, and alkaline phosphatase activity during the incubation suggested that the phytoplankton and heterotrophic prokaryotes (Hprok) communities were not P-limited at the sites. Furthermore, statistical comparison among treatments at the end of the incubation did not support a hypothesis of P-limitation at the three study sites. In contrast, primary production was consistently limited by N, and Hprok growth was not limited by N nor P in the Western Basin, but N-limited in the Ionian Basin, and N and P co-limited in the Levantine Basin. Our results demonstrated the gap between biogeochemical features (an apparent P-starved status) and biological responses (no apparent P-limitation). We question the general notion that Mediterranean surface waters are limited by P alone during the stratified period.

Citation: Tanaka, T., Thingstad, T. F., Christaki, U., Colombet, J., Cornet-Barthaux, V., Courties, C., Grattepanche, J.-D., Lagaria, A., Nedoma, J., Oriol, L., Psarra, S., Pujo-Pay, M., and Van Wambeke, F.: Lack of P-limitation of phytoplankton and heterotrophic prokaryotes in surface waters of three anticyclonic eddies in the stratified Mediterranean Sea, Biogeosciences, 8, 525-538, doi:10.5194/bg-8-525-2011, 2011.
 
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