Evolution of aquatic food web structures under cascade hydropower development in the upper yellow river

Cascade hydropower development has profoundly altered river hydrology and habitat configurations, driving fish community assembly and reshaping food web structure and function, with critical implications for ecosystem stability. We investigate temporal changes in fish food webs in the upper Yellow River, focusing on the Longyangxia-Liujiaxia cascade system, by integrating historical records with contemporary field surveys. Phase-specific food web models to quantify network complexity (species richness S, number of links L, link density LD, and connectance C) and stability (mean trophic level TL, omnivory O, modularity M, and quasi-stationary state QSS) across three hydropower development phases: pre-development, cascade development, and optimized operation. Cascade development expanded lentic and expanded increased habitat heterogeneity, shifting fish assemblages from migratory and rheophilic species toward resident and generalist species, while concurrently elevating the risk of non-native species invasions. Through predation, resource competition, and ecological niche displacement, non-native species restructured trophic interactions, lengthened food chains, and redirected energy flows, resulting in greater species richness and enhanced interspecific connectivity, and thereby increasing topological complexity. However, despite increases in link numbers, link density, trophic levels, omnivory, and modularity, the overall quasi-stationary state declined, indicating reduced local stability. These results reveal stage-specific complexity-stability trade-offs under intensive hydropower regulation and biological invasions, highlighting the need for integrated management strategies to balance engineering impacts, invasive species control, and ecological resilience in regulated river ecosystems.