HYDROFAT

Wider research context / theoretical framework: Freshwater ecosystems impacted by global warming receive higher influx of nutrients, may become eutrophic, and eventually turn darker. Such changes drive taxonomic shifts from nutritionally high to poor quality algae that provide fewer essential dietary polyunsaturated fatty acids (PUFA) to aquatic consumers, and thus inhibit somatic growth, reproduction, and eventually survival. The predicted impact of decreased dietary PUFA is a key problem in trophic ecology which requires a better understanding of PUFA synthesis, conversion and retention in aquatic organisms. Research questions / objectives / hypotheses: How do aquatic consumers supply their tissues with the essential nutrients to optimize survival in predicted warmer and darker waters? The broad objective of this proposal is to quantify; a) how aquatic invertebrates and fishes, particularly in fish neural and reproductive tissues, respond to dietary lipids to secure their lipid and FA demand under various diet, light, and temperature conditions (experimental approach); b) track the FA pathways to and within aquatic invertebrates and fishes using novel compound-specific stable isotopes (13-C and, for the first time, 2-H of FA) (biomarker approach); and, c) model spatial and seasonal variation in consumer dependence (aquatic invertebrates and fishes) on the elemental (including stable isotopes) and molecular (lipids and FA) composition of resources in eutrophic aquatic ecosystems (ecosystem approach). We hypothesize that; a) the PUFA biochemical conversion in consumers is temperature dependent, producing 2H depleted FA compared to dietary precursors and sources, and; b) the absence of dietary long-chain PUFA will increase endogenous PUFA conversion in fish liver cells that will subsequently route isotopically unaltered PUFA to neural, gonadal, and muscle tissues under all temperatures and ecosystems. Approach / methods: This research will quantify dietary lipid and FA adjustments in algae, zooplankton, benthic invertebrates, and fish tissues (liver, gonads, brain, retina, muscles), by using bulk and compound-specific hydrogen and carbon stable isotopes in experimental units and across a spatial gradient of eutrophic fish ponds. Level of originality / innovation: Hydrogen stable isotopes of fatty acids are introduced as novel tracers to identify sources and the metabolic fate of FA in aquatic organisms and hepatic, neural, gonadal, and muscle tissues of fish under global change impact scenarios. Modeling FA biochemistry through stable carbon and hydrogen isotopes will substantially increase our understanding of dietary energy transfer in aquatic food webs. Primary researchers involved: Martin Kainz (PI), Len Wassenaar (H isotopes), Matthias Pilecky (compound-specific stable isotopes), Fen Guo (experiments), Sami Taipale (plankton), Antonin Kouba (fish feeding), Tim Jardine (modeling).