Trophic fate of lipids in eutrophic aquatic ecosystems

Freshwater ecosystems are strongly impacted by global warming. Fishponds provide important diet fish for humans, yet they undergo severe stress via increasing temperature, nutrient supply and decreasing oxygen. The FWF project HydroFat will investigate how carp, as the most common pond fish in the world, can develop and survive in such harsh environmental conditions. The broad objective of this research is to; a) quantify how aquatic invertebrates and Common Carp, particularly in their neural and reproductive tissues, respond to dietary lipids to secure their lipid and fatty acid demand under various diet, light, and temperature conditions (experimental approach); b) track the fatty acid pathways to and within aquatic invertebrates and carps using novel compound-specific carbon and hydrogen stable isotopes (biomarker approach); and, c) model spatial and seasonal variation in consumer dependence (aquatic invertebrates and fishes) on the elemental and molecular composition of resources in eutrophic aquatic ecosystems (ecosystem approach). It is hypothesized that; a) the polyunsaturated fatty acid (PUFA) conversion in consumers is temperature dependent, producing 2H depleted PUFA 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. This research will quantify dietary lipid and fatty acid 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 fishponds. Hydrogen stable isotopes of fatty acids are introduced as novel tracers to identify sources and the metabolic fate of fatty acids in aquatic organisms and hepatic, neural, gonadal, and muscle tissues of fish under global change impact scenarios. Modeling fatty acids across various trophic levels of fishponds using stable carbon and hydrogen isotopes will substantially increase our understanding of dietary energy transfer in aquatic food webs and eventually to humans.