Abstract ID: 3.13896 | Accepted as Talk | Talk | TBA | TBA

Deglaciation in mountain catchments affects water sources and changes habitat conditions and resource availability in cold alpine rivers. While the consequences of glacier retreat for aquatic invertebrate biodiversity have been documented, its quantitative effects on food web structures, particularly on the production of periphyton, the biomass of invertebrates, and their nutritional quality, remain insufficiently understood. In this study, we assessed abiotic habitat conditions, periphyton biomass and composition, and invertebrate assemblages together with their individual body-mass across multiple glacierized and non-glacierized catchments in the Central Eastern Austrian Alps. The findings show that declining glacier cover reduces sediment load and runoff, increasing the stability of benthic habitats. These habitat ameliorations promote periphyton growth, particularly favoring diatoms and cyanobacteria, despite concurrent changes in nutrient availability. Increased periphyton biomass suggests a shift in basal resource quantity, with potential implications for its nutritional quality. This periphyton is key resource in alpine stream food webs, providing essential long-chain polyunsaturated fatty acids (LC-PUFA), crucial for somatic growth and reproduction of invertebrates. Our analysis of fatty acid (FA) composition in periphyton and invertebrates revealed that FA content varies across different stream typologies and degrees of glacial influence. However, invertebrates in glacier-fed streams appear to regulate their lipid composition endogenously rather than relying directly on dietary FA availability. This suggests physiological adaptations to low-PUFA environments, which could have consequences for energy transfer efficiency in alpine food webs during changing hydrological conditions. At higher trophic levels, decreasing glaciation affects invertebrate biodiversity but also the body-mass of typical species, with glacier-bound species exhibiting reduced body sizes. Given that FA composition influences consumer fitness and productivity, understanding these shifts is crucial for predicting future ecological changes in high-elevation river systems under the ongoing rapid habitat change throughout mountain regions. Our findings highlight the need for further research on the functional role of periphyton as a nutritional resource and its cascading effects on aquatic and terrestrial consumers, including fish and insectivorous birds.