JPR Advance Access originally published online on July 27, 2005
Journal of Plankton Research 2005 27(10):959-971; doi:10.1093/plankt/fbi049
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Copepod grazing impact on the trophic structure of the microbial assemblage of the San Pedro Channel, California
Department of Biological Sciences, University of Southern California, 3616 Trousdale Parkway, Los Angeles, CA 90089-0371, USA
* Corresponding Author: astrids{at}usc.edu
Received February 17, 2005; accepted in principle May 11, 2005; accepted for publication June 10, 2005; published online July 27, 2005
Communicating editor: K.J. Flynn
In August 2002 and March 2003 the trophic structure of the microbial assemblage from the San Pedro Channel, California was studied following the experimental alteration of the number of copepods. Changes in the abundance/biomass of microorganisms <80 µm during 3-day incubations were monitored in (i) the absence of metazoa >80 µm, (ii) the presence of natural abundances of metazoa and (iii) the presence of an elevated number of copepods. Prokaryotes and small-sized eukaryotes (<4 µm) dominated plankton biomass during both experimental months. Diatoms numerically dominated the 1080 µm plankton in August 2002, but ciliate and heterotrophic dinoflagellate biomass generally exceeded diatom biomass on both dates. Ingestion of protozooplankton (predominantly ciliates) contributed substantially to copepod daily carbon rations. The adult copepod assemblage removed 4.6 and 36% per day of the microzooplankton standing stocks (1080 µm size fraction) in August and March, respectively. Elevated copepod grazing pressure on protozooplankton resulted in increased biomass of nanoplankton (<5 µm) presumably via a trophic cascade. Accordingly, the copepodprotozoan trophic link appears to be a key factor structuring the planktonic microbial assemblage in the San Pedro Channel.
This paper is one of six on the subject of the role of zooplankton predatorprey interactions in structuring plankton communities.