The objective of the proposed project is to follow the fate of essential fatty acids from the primary producer through three trophic levels of a model freshwater food chain. This work is carried out by three research partners from Bulgaria, Romania, and Switzerland, which all contribute their individual competencies to address a transdisciplinary challenge.

Essential biomolecules are hypothesized to play a key role in the bottom-up structuring of food webs. Higher trophic levels are thought to be under strong selection to optimize their uptake and evolve in response to it. This, in turn, alters the flux of these biomolecules through the food web with corresponding consequences for consumer populations. This hypothesis is supported by ecosystem-wide studies as well as individual-based observations on single or two trophic levels. What is lacking, is a system that demonstrates these fluxes in detail through several levels of a food chain and, thus, provides a link between molecular and ecosystem data. Here, we propose an experimental approach that uses a tri-trophic model food chain consisting of primary producers (freshwater microalgae), first consumers (zooplankton), and second consumers (fish larvae) to manipulate and monitor the flux of long-chain polyunsaturated fatty acids (LC-PUFA). LC-PUFAs play a critical role for cell membrane ?uidity and the regulating of hormonal processes. Their de novo synthesis happens exclusively in microalgae, and their specific profiles vary among species and are influenced by environmental factors. We manipulate the production of LC-PUFAs at the primary level by varying cultivation conditions and document the response on the level of gene expression, growth parameters and LC-PUFA profile. Microalgae will then be fed to zooplankton, where again gene expression, growth and LC-PUFA profile will be assessed. Finally, zooplankton is fed to fish larvae, followed again by an analysis of growth, development, and LC-PUFAs. Thus, we create an ecologically relevant variation in the supply of LC-PUFAs at the level of the primary producer and monitor its consequences through the food chain, always considering the genetic response to the supply, the resulting alteration of the LC-PUFA profile, and the fitness consequences for the organism.

State-of-the-art analytics ensure reliable results. While the project’s overarching objective aims at answering a central topic in freshwater ecology, the knowledge gained from it will address further objectives, all of relevance for at least one the partners involved. The AgroBioInstitute Sofia, ABI, strengthens its competencies on metabolomics and functional genomics in an agrobiotechnological context; the Research Station for Aquaculture of the Alexandru Ioan Cuza University of Ia?i, UAIC, develops methodologies that are important for freshwater aquaculture and conservation biology; the aquaculture systems research group of the Zürich University of Applied Sciences, ZHAW, extends its work on production and processing of renewable resources from microalgae. Thus, the results of the project have implications beyond ecology and touch on several applied issues.

The four-year project brings together teams with complementary competencies to achieve this endeavour. The UAIC provides experience in aquaculture and aquatic ecology, the ABI is experienced in biomolecular analytics, and the ZHAW has experience in the cultivation of microalgae, zooplankton, and fish. Two PhD students, from Romanian and Bulgaria, respectively, will carry out transdisciplinary theses that are at the centre of this project and will work in all three partner institutions. This ensures a strong and lasting transfer of knowledge.

Keywords: food chain, fatty acids, trophic levels, essential biomolecules, aquaculture, gene expression, freshwater ecology