Investigating the efficacy of tidal wetland restoration in enhancing aquatic food web resources for native fishes

Abstract Introduction Endangered fish species, such as Delta smelt ( Hypomesus transpacificus ), in the San Francisco Estuary are threatened by a multitude of anthropogenic stressors. Tidal wetland restoration can partially mitigate these stressors by increasing food availability of aquatic invertebrate prey, but the efficacy of restoration remains unknown. Objective This study assesses changes in food web resource density and composition related to restoration efforts of multiple tidal wetlands within the upper San Francisco Estuary. Methods We monitored various aquatic invertebrate communities inside six restored tidal wetlands—along with reference sites—spanning up to 8 years. Invertebrate densities were analyzed using a Bayesian hierarchical model and compared both within a before‐after control‐impact and a control‐impact only framework. Changes in community compositions were analyzed using Permutational Multivariate Analysis of Variances. Results Invertebrate densities varied interannually at both restoration and reference wetlands. Although invertebrate densities in restored wetlands did not increase relative to densities in reference wetlands, restored wetlands still have comparable absolute densities of food resources for native fish. Specific analysis on Delta smelt prey items shows a similar pattern except in certain wetlands where prey species respond more favorably to restoration effects. Conclusions We detected mixed evidence for restoration effect on invertebrate densities within tidal wetlands, suggesting that restoration efforts can be one of multiple mitigation strategies in the recovery of endangered fish species.