Abstract
Many tidal wetland restoration projects have focused on changes in vegetation or avian communities to determine whether restoration efforts have been successful. However, a functioning restored ecosystem relies on complex interactions among organisms on every level of the food web. In 2008, more than 223 hectares (ha) of former dairy ranch were restored to tidal wetland in Tomales Bay, California. To evaluate changes, we monitored zooplankton, benthic invertebrate, and fish communities before and after restoration in the Project Area and several natural marshes. Zooplankton and benthic invertebrate communities differed from natural marshes prior to restoration, but began to converge with natural marshes after restoration in terms of species composition, richness, and diversity. Fish communities in the Project Area remained distinct from those of natural marshes after restoration, although abundance of non-native species decreased. In past studies, fish communities have changed more quickly than invertebrate ones. The divergent evolutionary path taken by this system may stem from differences in restoration approach. This project did not involve extensive excavation or fill with dredge spoil material, and this minimalistic approach may promote more rapid colonization by invertebrates, especially if source populations exist nearby. While convergence with natural marshes was an objective, rapid colonization may not be beneficial in this instance as natural marshes have turned out to be dominated by non-native, opportunistic invertebrate species. Ultimately, success of restoration projects may be determined by factors extrinsic to the project itself such as climatic variability and prevalence of invasive species within watersheds.
Highlights
The most widely studied indicators of change following wetland restoration are often parameters in which changes are readily visible—changes in vegetation communities or bird populations
Baseline Conditions Prior to restoration, zooplankton communities in the Project Area, Reference Areas, and Upstream Areas differed in abundance and species richness, diversity, and composition
While the restored Project Area did support three of the four most common benthic invertebrate species in natural marshes, differences in hydrologic regimes between Study Areas could lead to persistent differences in invertebrate species assemblages, even hydrology of these areas could begin to converge in the future due to salinity intrusion associated with sea level rise and changes in precipitation totals and patterns
Summary
The most widely studied indicators of change following wetland restoration are often parameters in which changes are readily visible—changes in vegetation communities or bird populations. Changes in higher trophic orders of fish and birds are often dependent on changes in their prey base following restoration. Species composition, and species diversity can change dramatically in the first few years after restoration with densities and species richness quickly resembling conditions observed in reference or natural marshes [1]-[6]. Some restored marshes have even supported higher fish densities and species richness than natural marshes [2] [3] and developed a species assemblage typical of reference marshes within 5 to 13 years [2] [4] [6]. There have been projects where fish use either did not compare favorably with reference marshes [7] or declined with restoration [8]. Rather than being driven by restoration, age of restoration, or native marsh status, several projects found that differences between fish assemblages depended on the marsh channels’ physical structure (e.g., width, depth, slope of bank, marsh elevation), as well as hydrologic and environmental conditions, including hydroperiod, temperature, dissolved oxygen, salinity, and flow discharge [1]-[3] [9]
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