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JPR Advance Access originally published online on February 3, 2006
Journal of Plankton Research 2006 28(4):385-397; doi:10.1093/plankt/fbi124
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© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Nanoheterotroph grazing on bacteria and cyanobacteria in oxic and suboxic waters in coastal upwelling areas off northern Chile

L. Antonio Cuevas1 and Carmen E. Morales1,2,*

1 Centro de Investigacion Oceanografica en el Pacifico Sur-Oriental (FONDAP-COPAS), Depto. Oceanografia, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile and 2 Estacion de Biologia Marina, Depto. Oceanografia, Universidad de Concepcion, Casilla 44, Dichato, Chile

* Corresponding Author: camorale{at}udec.cl

Received November 14, 2005; accepted in principle December 14, 2005; accepted for publication January 26, 2006; published online February 3, 2006
Communicating editor: K.J. Flynn

The vertical distribution and abundance of microbial assemblages and the grazing of nanoheterotrophs upon prokaryotes in oxic and suboxic waters were examined in two coastal upwelling areas off northern Chile where a shallow Oxygen Minimum Zone (OMZ) is characteristic. Prokaryotic prey included bacterioplankton and cyanobacteria (Synechococcus); both displayed a bimodal distribution, with abundance maxima above and within the upper OMZ. Flagellates numerically dominated the nanoplankton and were mostly concentrated in the oxic layer. Mean ingestion rates of cyanobacteria by nanoflagellates (vacuole content method) ranged from 0.2 to 1.1 cells flagellate–1 h–1 and mean consumption rates (34–160 cells mL–1 h–1) were four times higher in the oxic layer. With the selective inhibitors technique, specific grazing rates on bacteria were low (<0.1 h–1) and consumption did not control bacterial production in the surface layer but did so in the suboxic layer (accounting for >100% of bacterial production). With the same method, the specific grazing rate on cyanobacteria ranged between zero and 0.23 h–1 with no clear differences between oxygen conditions; prey growth and production were always higher than the grazing pressure (accounting for <17% of cyanobacterial production). The impact of grazing by nanoheterotrophs in regulating the production of prokaryotes in oxic and suboxic waters in this region is discussed.


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