Effects of plankton community structure on energy pathways and tropic efficiency (PATH)

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A current challenge to ecologists is to predict how compositional shifts at the base of the aquatic food web propagate up to higher trophic levels. Energy or resource availability for upper trophic levels is governed by food-chain length and by factors that regulate the rate of energy transfer from primary producers to consumers. The goal of this project is to test the overall prediction that phytoplankton community structure and species composition are key regulators of energy and food quality transfer to mesozooplankton. We will (i) test the stability of fatty acid-specific δ13C isotope between the phytoplankton-zooplankton interface, which will be an important requirement as biomarker for trophic interactions, and (ii) manipulate natural microbial species composition and bacterial activity in mesocosms and measure carbon and nutritional transfer efficiency to copepods and their interactive effects with appendicularians. Copepods are a key link for carbon and nutritional flux and appendicularians are abundant filter-feeding organisms that are expected to increase with climate warming. Trophic efficiency will be estimated from production rates, dietary sources and nutritional transfer using combined fatty acid-specific δ13C isotope biomarkers. An improved understanding on how shifts in food-web structure affects energy and carbon flux through the plankton food web will be important because these processes have profound influence on fisheries and climate.