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Aquatic Microbial Ecology

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AME 51:169-181 (2008)  -  DOI:

Heterotrophic nanoflagellate and ciliate bacterivorous activity and growth in the northeast Atlantic Ocean: a seasonal mesoscale study

Hera Karayanni1,2,3,*, Urania Christaki2,4, France Van Wambeke1, Melilotus Thyssen1, Michel Denis1

1Laboratoire de Microbiologie, Géochimie et Ecologie Marines, UMR 6117, CNRS, Université de la Méditerranée, Campus de Luminy, case 901, 13288 Marseille Cedex 9, France
2Hellenic Centre for Marine Research, PO Box 712, 19013 Anavissos, Greece
3Present address: Department of Ichthyology & Aquatic Environment, School of Agricultural Sciences, University of Thessaly, 38446 Nea Ionia, Greece
4Present address: Laboratoire d’Océanologie et de Géosciences, CNRS, UMR LOG 8187, Université du Littoral Côte d’Opale (MREN), 32 avenue Foch, 62930 Wimereux, France

ABSTRACT: The grazing effect of heterotrophic nanoflagellates (HNF) and ciliates on bacterial production (BP), as well as their growth rates, was studied in winter, spring and autumn 2001 during the French research project Programme Océan Multidisciplinaire Méso-Echelle (POMME) in the northeast Atlantic Ocean (38 to 45° N, 16 to 22° W). The variability of different parameters studied appears to be largely controlled by the seasonal and latitudinal gradients of primary production rather than the strong eddy activity at the mesoscale level in the area. Heterotrophic microbial abundance, biomass and protistan grazing varied temporally, presenting highest values during the phytoplankton bloom, during the spring period and following the northward propagation of the bloom. HNF biomass integrated over the upper 100 m was highest in spring (270 to 850 mg C m–2). Ciliate integrated biomass was generally ≤160 mg C m–2 except in a Tintinnus sp. bloom in a northern anticyclonic eddy (A1) in spring when it reached 637 mg C m–2. HNF and ciliate growth rates varied from 0.2 to 0.7 d–1 and 0.2 to 1.4 d–1, respectively. The fraction of BP consumed by ciliates was generally <10% except in the anticyclonic eddy A1 in spring during a tintinnid bloom when it reached 37% of BP. In conclusion, our data revealed that HNF can remove a large fraction of bacterial production in the northeast Atlantic Ocean (83 ± 27%, average of all sampling sites and seasons). Ciliates transferred less carbon to higher trophic levels than did HNF; however, episodic high occurrence of large bacterivorous ciliates, primarily tintinnids, increased the role of theses organisms as C-links in the microbial food web.

KEY WORDS: Heterotrophic nanoflagellates · Ciliates · Tintinnids · Bacterivory · Ingestion rates · Growth rates · Atlantic Ocean

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Cite this article as: Karayanni H, Christaki U, Van Wambeke F, Thyssen M, Denis M (2008) Heterotrophic nanoflagellate and ciliate bacterivorous activity and growth in the northeast Atlantic Ocean: a seasonal mesoscale study. Aquat Microb Ecol 51:169-181.

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