Tidal restoration of a managed wetland in California favors non‐native fishes

Abstract

Tidal wetland restoration is commonly used to recover ecosystem functions and services that were lost when wetlands were diked for reclamation or management. Less research has been conducted on the response of invertebrate and fish assemblages to tidal restoration than on plants and physical attributes. Blacklock Marsh, a wetland in Suisun Marsh, USA, was once managed for waterfowl hunting and cattle grazing until its dike was breached, restoring full tidal action. We sampled water quality, zooplankton, macroinvertebrates, and fishes in Blacklock Marsh, and compared these metrics to adjacent naturalistic waterways and to a managed wetland focused on waterfowl. Our goal was to compare food production and community assemblage on a restoring marsh to other types of nearby waterways. Blacklock Marsh had less chlorophyll‐ a and dissolved organic carbon than nearby dead‐end sloughs and the managed wetland, less zooplankton biomass than the managed wetland, and lower fish diversity—with a fish assemblage dominated by non‐native species—compared to all other waterways. The most abundant fish species in the restoring site, Mississippi silverside ( Menidia audens ), is a non‐native fish and known predator of Delta smelt larvae ( Hypomesus transpacificus ), for which the restoration was targeted. Our research suggests that restoring tidal action to managed wetlands alone may worsen rather than improve conditions for at‐risk and native fishes.