SS2.01 Effects of Biotic Interactions on the Structure and Function of Microbial Food Webs
Date: Wednesday, June 12, 2002
Location: Poster Session - VCC
 
TadonlékéRD, Université du Québec à Montréal-GEOTOP, C. P. 8888, Succ. Centre ville, H3C 3P8, Montréal, Canada, c1714@er.uqam.ca
Planas, D, , Université du Québec à Montréal-GEOTOP, C. P. 8888, Succ. Centre ville, H3C 3P8, Montréal, Canada, planas.dolores@uqam.ca
Lucotte, M, M, Université du Québec à Montréal-GEOTOP, C. P. 8888, Succ. Centre ville, H3C 3P8, Montréal, Canada, lucotte.marc_michel@uqam.ca
 
TOP-DOWN EFFECTS OF MACROGRAZERS ON MICROBIAL COMMUNITIES IN BOREAL RESERVOIRS
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The food web structure of northern boreal reservoirs is poorly known. We experimentally tested the impact of grazers on the components of the microbial web in oligotrophic reservoirs of the James Bay region, using short-term (24 h) in-situ incubations, in the presence (MG+) or absence (MG-) of grazers. The species composition of ciliates was modified in MG+ but ciliate growth rates not always differ between treatments. Heterotrophic nanoflagellates (which comprised mainly cells with size < 10 μm) growth was systematically higher in MG- than in MG+. Active bacteria (bacteria with high nucleic acid content after dye staining, enumerated using flow cytometry) and total bacterial growth was also higher in MG- and in treatments were all predators were removed. Our results (i) suggest that macrozooplankton have strong impact on the dynamics of microorganisms (composition and carbon flow) in these boreal freshwaters and (ii) seem to support the fact that active bacteria are responsible for most of the bacterial production in aquatic systems.