SS2.01 Effects of Biotic Interactions on the Structure and Function of Microbial Food Webs
Date: Wednesday, June 12, 2002
Time: 10:30:00 AM
Location: Saanich
 
ZoellnerE, Max Planck Institute for Limnology, Ploen, GERMANY, zoellner@mpil-ploen.mpg.de
Gasol, J, M, Institut de Cičncies del Mar-CMIMA,CSIC, Barcelona, Spain, pepgasol@icm.csic.es
Juergens, K, , Max Planck Institute for Limnology, Ploen, Germany, juergens@mpil-ploen.mpg.de
 
STRUCTURING EFFECTS OF DIFFERENT MESOZOOPLANKTON COMMUNITIES ON MICROBIAL FOOD WEB COMPONENTS - A MARINE EXAMPLE
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Different mesozooplankton groups are expected to trigger different predation cascades on the bacterioplankton due to differences in feeding behaviour and the prey spectrum. A large scale mesocosm experiment with 24 enclosures was performed in the Trondheimsfjord (Norway) with naturally occurring phyto-, protozoo- and bacterioplankton being exposed to a density gradient of different types of mesozooplankton, selectively feeding copepods and filter-feeding appendicularians respectively. Increasing copepod grazing caused a decrease of larger ciliates followed by a strong increase of nanoflagellates and autotrophic picoplankton. After one week bacterial abundance and production had almost doubled in treatments without mesozooplankton. In copepod enclosures the abundance of bacteria with high DNA content and high respiratory activity as well as bacterial production increased from low to high copepod densities, which can mainly be referred to an increasing proportion of persisting HNF-grazing resistant bacteria. After 9 days a bloom of appendicularians could be observed and bacterial abundance and productivity was reduced by more than 50 %. All alterations in bacterial production and activity were accompanied by changes in taxonomic composition of the bacterial assemblage as ascertained by DGGE.