Multitrophic responses to tidal marsh restoration: early effects of channel configuration on water quality, aquatic food web structure, and fish communities

Introduction Tidal wetland restoration is critical for reversing habitat loss and enhancing resilience under sea‐level rise and climate variability. Dutch Slough in the San Francisco Estuary served as a living laboratory for adaptive management. Objectives We assessed early ecological outcomes of restoration design, focusing on how channel length, complexity, and connectivity influence recovery and habitat quality. Methods Two constructed tidal channels and one open‐water feature were monitored from 2021 to 2023 using a Before‐After‐Reference‐Impact (BA:RI) framework within a living laboratory approach. Mixed‐effects BA:RI models isolated restoration effects. Data collection integrated water‐quality sensors, zooplankton and fish imaging, and fish environmental DNA (eDNA). We evaluate aquatic food‐web responses using indicators spanning primary producers, zooplankton, and fish assemblages. Results Pre‐breach (2021): Three functionally isolated food webs formed, and water quality differed significantly from reference sites. Post‐breach (2022–2023): Conditions shifted toward reference states, with improved dissolved oxygen, dynamic turbidity, and reduced chlorophyll‐ a linked to shorter residence times and enhanced tidal mixing. Despite lower chlorophyll‐ a concentrations, patterns supported altered production pathways characterized by rapid turnover rather than reduced production, suggesting a shift toward export and trophic transfer rather than diminished productivity. Longer, complex channels supported greater habitat heterogeneity, higher zooplankton and juvenile fish densities near vegetated margins, and increased species richness. eDNA and video detected rapid post‐breach fish taxa increases, including seasonal native expansion amid persistent non‐native dominance. Conclusions Channel length, complexity, and connectivity strongly influence ecological rehabilitation. Adaptive management accelerates functional restoration and improves nursery‐habitat quality.