Restored tidal wetlands may provide important food web support for at-risk fish species in the Sacramento-San Joaquin Delta (Delta) of California, including Delta Smelt (Hypomesus transpacificus) and Chinook Salmon (Oncorhynchus tshawytscha). Since many tidal wetland restoration projects are planned or have recently been constructed in the Delta, understanding the diversity and variability of wetland invertebrates that are fish prey items is of increasing importance. During this study, two different invertebrate sampling techniques were tested (leaf packs and sweep nets) in four habitat types within three different wetland areas to evaluate which sampling technique provided the most reliable metric of invertebrate abundance and community composition. Sweep nets provided a better measure of fish food availability than leaf packs and were better able to differentiate between habitat types. Generalized linear models showed submerged and floating vegetation had higher abundance and taxa richness than channel habitats or emergent vegetation. Permutational multivariate analysis of variance showed significantly different communities of invertebrates in different habitat types and in different wetlands, and point-biserial correlation coefficients found a greater number of mobile taxa associated with sweep nets. There were more taxa associated with vegetated habitats than channel habitats, and one area had more taxa associated with it than the other two areas. These results suggest that restoration sites that contain multiple habitat types may enhance fish invertebrate prey diversity and resilience. However, the effect of habitat diversity must be monitored as restoration sites develop to assess actual benefits to at-risk fish species.

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28Restored tidal wetlands may provide important food web support for at-risk fish species in the 29 Sacramento-San Joaquin Delta (Delta) of California, including Delta Smelt (Hypomesus 30 transpacificus) and Chinook Salmon (Oncorhynchus tshawytscha). Since many tidal wetland 31 restoration projects are planned or have recently been constructed in the Delta, understanding the 32 diversity and variability of wetland invertebrates that are fish prey items is of increasing 33 importance. During this study, two different invertebrate sampling techniques were tested (leaf 34 packs and sweep nets) in four habitat types within three different wetland sites to evaluate which 35 sampling technique provided the most reliable metric of invertebrate abundance and community 36 composition. Sweep nets provided a better measure of fish food availability than leaf packs and 37 were better able to differentiate between habitat types. Generalized linear models showed 38 submerged and floating vegetation had higher abundance and species richness than channel 39 habitats or emergent vegetation. Permutational multivariate analysis of variance showed 40 significantly different communities of invertebrates in different habitat types and in different 41 wetlands, and point-biserial correlation coefficients found a greater number of mobile taxa 42 associated with sweep nets. There were more taxa associated with vegetated habitats than 43 channel habitats, and one region had more taxa associated with it than the other two regions. 44These results suggest that restoration sites that contain multiple habitat types may enhance fish 45 invertebrate prey diversity and resilience. However, the effect of habitat diversity must be 46 monitored as restoration sites develop to assess actual benefits to at-risk fish species. 47 48 3 49Tidal wetlands provide an important source of productivity to many estuaries worldwide, 50 subsidizing the surrounding open-water areas with vascular plant detritus, phytoplankton, 51 zooplankton, and nekton biomass [1][2][3][4][5]. Productive freshwater tidal wetlands dominated the 52 landscape of California's Sacramento-San Joaquin Delta (Delta) prior to the Gold Rush, but, by 53 1930, the vast majority of wetlands were reclaimed, primarily for agriculture [6] (see Fig 1A). 54While there is currently no quantitative estimate of the impact of wetland loss on aquatic primary 55 productivity, production most likely declined drastically post-reclamation [7]. 56 57 Figure 1. A) Map of California (USA) with the San Francisco Bay-Delta watershed. The inset is 58 a finer-scale map of the Legal Delta, with the focal area in the Cache Slough Complex outlined 59 with a dashed box. B) The Cache Slough complex, with sampling regions circled. Each region 60 contained four sampling sites with different habitat types: SAV, FAV, EAV, and channel. 61 62 Restoration of tidal wetland habitat in the Delta may increase overall primary and secondary 63 production, and thus multiple regulatory mandates now include tidal wetland restoratio...

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Wetland restoration is a key management tool for increasing food availability for at-risk fishes in the San Francisco Estuary. To characterize the benefits of restoration sites, it is critical to quantify the abundance and composition of fish food resources in and near the wetlands. Characterization of zooplankton communities is considered particularly important, but accurate analysis of zooplankton samples is time-consuming and expensive. The recently established Fish Restoration Program (FRP) Monitoring Team assessed whether data from existing long-term monitoring surveys could be used to characterize shallow-water zooplankton communities before restoration. During the springs of 2017 to 2019, the FRP collected zooplankton samples near the mouth of tidal wetland sites, or immediately outside future restoration sites, and compared them to concurrent samples collected in deep water by existing long-term monitoring surveys. We found very few differences in community composition between shallow and deep samples, though a few taxa were more abundant in shallow water. Seasonal and interannual differences in composition and abundance showed that restoration sites provide varying food resources over time. There was significantly higher total abundance of zooplankton in deep versus shallow water, which may be a result of differences in zooplankton production, migration, or fish predation. Inconsistencies in towing speed and gear type may also be driving this result, rather than true habitat differences. This study indicates that monitoring of wetland restoration sites must rely on multiple years of data collected on the site—rather than relying on adjacent open-water sampling—and should include monitoring of epiphytic and epibenthic invertebrates as well as zooplankton.

Just like people, fish need a safe place to find food and grow up. For fish that travel between fresh water and the ocean, tidal wetlands are a perfect neighborhood, with lots of habitat and food. Tidal wetlands are areas of shallow water where tides from the ocean cover the land with water every day. Besides providing a home for fish and water-loving plants, tidal wetlands also help protect people and their property from natural disasters like storms, and from sea-level rise. People have not always understood the value of wetlands, so billions of acres of them have been filled to farm or build on. In the San Francisco Estuary, more than 90% of wetlands were converted to other uses in <150 years! People now understand why wetlands are important, so protecting and restoring wetlands is a top priority.