Hydrodynamic and trophic variations reshape macroinvertebrate food webs in urban ecosystems.

Urbanization is modifying aquatic ecosystems, with hydrodynamic and trophic variations altering biotic assemblages in rapidly expanding cities worldwide. Despite the fundamental bioenergetic role of food webs within these assemblages, their responding mechanism to the hydrodynamic and trophic variations remains largely unknown. Here we show that hydrodynamic and trophic loss, coupled with the weakening of cascade controls by key trophic guilds, leads to a significant decline in the structure, function and stability of macroinvertebrate food webs. Utilizing the allometric diet breadth model and biomass balance model, we established representative food webs for macroinvertebrate groups under varying hydrodynamic and trophic stresses. We found that such losses have reduced ∼75% trophic guild richness, ∼85% biomass flux, and ∼80% biomass storage. These reductions promote trophic guild specialization, further destabilizing food web, eroding interactive strength asymmetry, and diminishing the control of trophic guilds. Furthermore, macroinvertebrate food webs show divergent stability responses under similar stress levels, mainly driven by differences in the cascade controls exerted by key trophic guilds. Our results underscore the critical role of hydrodynamic and trophic variations in shaping urban aquatic ecosystems and highlight the significance of both external environmental revitalization and internal food web dynamics enhancement in restoring the ecological stability in urban settings.