Silverside gold mine? Restored tidal habitats host abundant invasive fishes in a novel California marsh (U.S.A.)

Abstract Introduction Novel ecosystems, where environmental conditions have been fundamentally altered from a historic norm, require nontraditional approaches to restoration. Suisun Marsh, located within California's San Francisco Estuary (SFE), is a novel, brackish water wetland complex, where managers have begun restoring tidal connectivity to wetlands in attempts to expand productive shallow‐water habitat and reverse declines of threatened native fishes. Objectives We compared the nearshore habitats of tidally restored wetlands to that of other, extant habitats in the marsh, to assess how each benefits target fish species. Methods For 18 months, we sampled water quality, plankton densities, and fish assemblages at nine sites across the three nearshore habitat types in Suisun: restored tidal wetlands, gated seasonally managed wetlands, and open‐water slough channels. Results Overall, fish assemblages in both restored tidal wetlands and slough channels were dominated by invasive Mississippi silverside ( Menidia audens ). In managed wetlands, silverside was rarely captured, and native resident three‐spined stickleback ( Gasterosteus aculeatus ) dominated catch. Managed wetlands demonstrated higher plankton densities compared to restored or slough habitats, potentially because of longer water residence times and/or production stimulus from seasonal flood‐drain cycles. Conclusion Our results suggest that the conversion of managed wetlands to open tidal restorations may reduce habitat with unique functionality and species assemblages within Suisun Marsh.