Fragmented coexistence and spatial decoupling in estuarine macrobenthos driven by an artificial flood event

Currently, how estuarine biomes respond to river regulation has become a globally concerned issue, yet the assembly mechanisms shaping diversity patterns and species coexistence in estuarine macrobenthos following such events are poorly understood. To address this gap, we applied a suite of multi-scale approaches, integrating spatial variation partitioning, β diversity decomposition, as well as niche and network theories, to dissect community shifts across a typical artificial flood event in the Yellow River Estuary. Results revealed this event fundamentally reconfigured the assembly rules, biogeographic structure, and coexistence architecture of estuarine macrobenthic communities through a tripartite mechanistic response: (i) environmental filtering strengthened as a selective sieve (pure environmental fraction increasing from 21.15% to 30.49%), while stochastic processes, particularly ecological drift, simultaneously gained prominence (unexplained variation rising from 15.00% to 24.37%); (ii) a consequent spatial decoupling that fractures the estuarine continuum into a high-turnover near-estuary and a buffered, high-similarity far-estuary; and (iii) the emergence of divergent coexistence architectures within these regions from structured niche partitioning in the far-estuary to modular networks of opportunistic annelids in the near-estuary. Our work elucidates how artificial floods reconfigure estuarine macrobenthos communities by shifting assembly rules, leading to a more fragmented community structure. These findings provide a critical mechanistic basis for informing adaptive management strategies to address ecological challenges posed by river management and climate change. • Artificial flood intensifies environmental filtering (21% to 30%) while amplifying ecological drift (15% to 24%), resetting estuarine assembly rules. • This drives spatial decoupling, with the near-estuary characterized by high turnover and the far-estuary maintaining high similarity ( β T , 0.54 to 1.13). • Coexistence becomes fragmented, with connected molluscan networks in the far-estuary and modular annelid-dominated networks in the near-estuary. • Flood disturbance reconfigures macrobenthic assembly and biogeographic patterns, requiring spatially explicit management to sustain estuarine ecological integrity.