EFFECTS OF DISSOLVED ORGANIC CARBON (DOC) AND ZOOPLANKTON GRAZING PRESSURE ON BACTERIA AND CILIATES

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2021-11-24
Yetim, Sinem
Global climate change results in extreme precipitation events that increase allochthonous organic matter (e.g., dissolved organic carbon, DOC) input into freshwater ecosystems via flooding. While DOC is a source of carbon and energy for heterotrophic organisms in freshwater ecosystems, its bottom-up effects on trophic interactions, and especially on the microbial food web, are poorly understood. Similarly, the top-down effect of contrasting zooplankton traits (i.e., generalist vs. selective) on DOC enriched food webs is also unknown. We compared both the bottom-up effects of DOC types (e.g., leaf-leachate DOC, HuminFeed®) and the top-down effects of zooplankton with contrasting grazing selectivity on the biomass and composition of microbial food webs (i.e., bacteria and ciliates) in a series of laboratory experiment and in-situ mesocosm grazing assays. We predicted that the total biomass of bacteria and ciliates were enhanced by DOC addition, especially with leaf leachate DOC, and reduced by zooplankton. Additionally, we expected that copepods would have higher grazing pressure on ciliates than Daphnia due to grazing mode. We found both DOC types and zooplankton had nonsignificant effect on bacteria biomass. DOC, especially leaf-leachate DOC, had a positive effect on ciliate biomass, while zooplankton had a negative effect. In general, the top down effect was in general stronger than the bottom-up effect and the strongest zooplankton effect was in the copepod – ciliate link. DOC had nonsignificant effect on the functional feeding groups of ciliates, and copepods reduced relative biomass of algivore and nonselective ciliates that was a novel proof of selectivity of copepods.

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Citation Formats
S. Yetim, “EFFECTS OF DISSOLVED ORGANIC CARBON (DOC) AND ZOOPLANKTON GRAZING PRESSURE ON BACTERIA AND CILIATES,” M.S. - Master of Science, Middle East Technical University, 2021.