SS2.01 Effects of Biotic Interactions on the Structure and Function of Microbial Food Webs
Date: Wednesday, June 12, 2002
Location: Poster Session - VCC
 
CowlishawRJ, University of Oregon/Oregon Institute of Marine Biology, Charleston, USA, rjc@darkwing.uoregon.edu
Shapiro, L, P, University of Oregon/Oregon Institute of Marine Biology, Charleston, USA, lshapiro@oimb.uoregon.edu
 
NON-LINEAR RELATIONSHIPS IN DILUTION GRAZING EXPERIMENTS: THE IMPLICATON OF PREDATOR-PREY INTERACTIONS WITHIN THE MICROZOOPLANKTON
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The dilution method has become the standard technique for estimating the grazing impact of microzooplankton on phytoplankton production. Grazing saturation due to a modulated feeding response of the microzooplankton at low dilution is frequently used as an explanation of non-linearity between ingestion and consumer density. Experimental results described here suggest that non-linear relationships between the apparent growth of autotrophic picoplankton (Apico) and dilution factor can be due to predator-prey interactions within the microzooplankton assemblage. A 25% dilution produced a significant increase in the apparent growth of heterotrophic nanoflagellates (Hnan) and suppression of Apico apparent growth. In another dilution series, the density of larger microzooplankton was initially reduced with a 20 mu-m screen. A significant increase in Hnan apparent growth was observed in the undiluted treatments compared to the same treatments with unscreened water; but no increase was observed in the 25% dilution treatments. Furthermore, the non-linear relationship between Apico apparent growth and dilution factor was not observed with the reduction of larger microzooplankton density.