Aquatic–terrestrial linkages: Export of polyunsaturated fatty acids from aquatic ecosystems via emerging insects and potential consequences for terrestrial invertebrate consumers

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Cross-ecosystem fluxes of organic matter can crucially influence the productivity of adjacent habitats. Emerging aquatic insects provide an important pathway by which freshwater-derived organic matter can enter terrestrial food webs. Effects of reciprocal resource subsidies on adjacent food web processes depend on the quantity of the subsidy; if and how qualitative differences in resource subsidies can influence adjacent food web processes has not been studied yet. The objective of this project is to evaluate the transfer of essential and potentially limiting biochemical nutrients, i.e. polyunsaturated fatty acids (PUFA), from freshwater to terrestrial systems via emerging insects and to assess the significance of freshwater-derived PUFA for terrestrial invertebrate consumers. Emergence traps will be installed on different lake ecosystems to assess habitat-specific PUFA fluxes. Pond experiments with stable isotope-labelled substrates will be used to assess PUFA export via emerging insects and distribution of aquatic PUFA in adjacent terrestrial ecosystems and invertebrate consumers. Laboratory feeding experiments will be conducted with riparian invertebrate predators (i.e. spiders), aquatic and terrestrial insect prey and PUFA-manipulated food to test whether aquatic insects are preferentially consumed and support the growth of riparian predators more efficiently than terrestrial insect prey. This approach will provide novel insight into the potential role of essential nutrients in mediating cross-ecosystem effects.