COMBINED EFFECTS OF DISSOLVED ORGANIC CARBON AND ZOOPLANKTON GRAZING ON PHYTOPLANKTON COMMUNITY

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2022-6-22

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Metin, Melisa

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While global climate change has major impacts on freshwater ecosystems, a mechanistic understanding of these effects on food web dynamics is poorly understood. A key effect of climate change is increased allochthonous dissolved organic carbon (DOC) input to aquatic environments, which serves as an energy source for heterotrophic plankton and alters food web dynamics, and leads brownification. We aimed to link patterns and processes in a plankton ecosystem by comparing the bottom-up effects of DOC (i.e., recalcitrant and leaf leachate sources) to the top-down effects of zooplankton with contrasting grazing selectivity (Daphnia vs. calanoid copepods) on phytoplankton biomass and composition in laboratory and in-situ mesocosm grazing assays. We expected that DOC and zooplankton would reduce phytoplankton biomass; stronger herbivory by Daphnia than copepods; and stronger grazing on larger-sized phytoplankton. In the nutrient replete laboratory experiment, DOC reduced total phytoplankton biomass (especially smaller sized species). While grazers reduced total phytoplankton, they increased smaller phytoplankton and decreased larger phytoplankton biomass. Moreover, copepods were stronger herbivores than Daphnia. In nutrient limited mesocosm experiments DOC increased phytoplankton biomass, though species-specific responses varied across treatments and time. Hence, labile DOC may reduce phytoplankton biomass in nutrient replete conditions, and increase phytoplankton during nutrient limitation. Mesozooplankton grazing is expected to reduce mostly larger sized phytoplankton (~20µm), with calanoid copepods having a stronger mass-specific effect than Daphnia. Results highlight the DOC quality’s roles, nutrient and light limitation, microbial grazing, and meso-zooplankton traits as key regulators of phytoplankton community dynamics and plankton trophic interactions in a changing world.

Subject Keywords

Phytoplankton, Food Web, Selectivity, DOC, Leaf-leachate

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https://hdl.handle.net/11511/98140

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

M. Metin, “COMBINED EFFECTS OF DISSOLVED ORGANIC CARBON AND ZOOPLANKTON GRAZING ON PHYTOPLANKTON COMMUNITY,” M.S. - Master of Science, Middle East Technical University, 2022.