Emerging aquatic insects are often rich in essential polyunsaturated fatty acids (PUFAs), which are important for a variety of physiological functions in animals, including growth, reproduction, and immunity efficiency. Furthermore, these insects with aquatic larval stages represent a highly nutritious food source for riparian and terrestrial predators, such as spiders, and play an important role for the linkage and the resource flow between aquatic and terrestrial systems. In this study, we investigate the coupling between the fatty acids (FA) and amino acids (AA) trophic transfer using compound-specific stable isotope analysis (CSIA) and mixing models. We discuss (dis)similarities, as well as (dis)advantages of the different approaches used to quantify the aquatic resource dependency of ground-dwelling (active hunters) and web-building spiders collected along a riparian-terrestrial gradient (0 – 100 m distance from a stream). While mixing models using MixSIAR based on CSIA-AA data of essential AAs (Ile, Leu, Phe and Val) revealed clear results (i.e., stronger aquatic resource dependency of ground-dwelling spiders), the results from mixing models based on fatty acids were less robust, and their interpretation requires more caution. We here propose the use of both CSIA-AA and FA simultaneously to achieve the most robust results and to describe the organic matter fluxes in food webs most accurately, and additionally allow conclusions on dietary preferences of consumers and the dietary quality of their prey.

Primary Presenter: Maja Ilić, Federal Institute for Forest, Snow and Landscape Research (WSL) (maja.ilic.bio@gmail.com)

Authors:

Grégoire Saboret, Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Department of Surface Waters – Research and Management  ()

Bastiaan Drost, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Forest Health and Biotic Interactions & Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Department of Surface Waters – Research and Management  ()

Carmen Kowarik, Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Department of Aquatic Ecology  ()

Carsten Schubert, Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Department of Surface Waters – Research and Management & Swiss Federal Institute of Technology, Department of Biogeochemistry and Pollution Dynamics  ()

Martin Gossner, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Forest Health and Biotic Interactions  ()