Does tidal marsh restoration lead to the recovery of trophic pathways that support estuarine fishes?

Breeding bird response to habitat rehabilitation after anthropogenic disturbance has received little attention in the Arctic. The North Slope of Alaska is an important breeding ground for many populations of migratory birds and has also supported major oilfields since the late 1960s. The most obvious impacts of industrial development to nesting birds are direct habitat loss and fragmentation resulting from the construction of infrastructure, along with increased mechanical noise, vehicle traffic, and other forms of anthropogenic disturbance. In response to state and federal requirements, efforts have been made to rehabilitate abandoned portions of the oilfields. We compared bird use at rehabilitation sites and at nearby paired reference sites. Densities of shorebirds and passerines varied between rehabilitation sites and reference sites, but waterfowl densities did not. Specifically, passerine and shorebird densities were higher at reference sites in the early or mid-season and lower at reference sites in the late season. Additionally, birds on rehabilitation sites were primarily observed foraging and resting, while behavior observed on paired reference sites was more diverse and included courtship displays, nesting, and aggression. Further, rehabilitation sites supported significantly fewer nests and fewer species than recorded at reference sites. Our findings suggest that sites 3 to 10 years post rehabilitation do not provide bird habitat comparable to nearby reference sites and, by extension, do not provide shorebird and passerine habitat comparable to that found prior to development. However, rehabilitation sites appear to provide adequate habitat for waterfowl and are important to shorebirds and passerines as foraging areas. Continued monitoring will be needed to establish the long-term suitability of rehabilitation sites, compared to reference sites, as breeding habitat for birds.

The Okaloosa Darter Etheostoma okaloosae is a small percid endemic to six stream drainages in northwestern Florida. The U.S. Fish and Wildlife Service listed Okaloosa Darters as endangered in 1973 and downlisted them to threatened in 2011 because of habitat improvements and increasing abundance across much of their geographic range. Delisting is possible if remaining recovery criteria are met, including restoration of degraded stream reaches. Impounded reaches of Anderson Branch, Mill Creek, and Toms Creek were restored by removing impediments to water flow, draining impoundments, and reconstructing stream reaches. Restorations of Anderson Branch and Mill Creek were designed to rehabilitate populations of Okaloosa Darters without significantly affecting popular recreational activities at these locations. Restorations were evaluated from 2007 to 2013 by comparing counts of Okaloosa Darters and the composition of microhabitats in restored and nearby undisturbed reference sites. Okaloosa Darters were absent from degraded stream reaches at the beginning of the study, but they rapidly colonized once restorations were completed. Counts of Okaloosa Darters in reference and restoration sites in Anderson Branch were similar by the end of the study, whereas counts in restoration sites were significantly lower than nearby reference sites in Mill and Toms creeks. Restoration sites tended to have lower coverage of sand and root and higher coverage of macrophytes. As riparian vegetation surrounding restoration sites matures to a closed canopy that reduces excessive growth of macrophytes, stream microhabitats and numbers of darters will probably become similar to reference sites. Restoration of degraded stream sites increased abundance and distribution of Okaloosa Darters and reconnected formerly isolated upstream and downstream populations. These projects demonstrated that restoration is a useful conservation tool for imperiled fishes such as Okaloosa Darters and can be undertaken without interfering with popular recreational activities. Received March 9, 2016; accepted August 15, 2016 Published online November 7, 2016

Tidal marshes are among the most threatened habitats on Earth because of their limited natural extent, a long history of human drainage and modification, and anticipated future sea‐level rise. Tidal marshes also provide services to humans and support species of high conservation interest. Consequently, millions of dollars have been spent on tidal marsh restoration throughout North America. Southern New England has a long history of tidal marsh restorations, often focused on removal of the invasive plantPhragmites australis. Working in 18 Connecticut marshes, we examined the bird community in 21 plots in restoration sites and 19 plots in reference sites. Restoration plots were divided into those in marshes where management involved restoring tidal flow and those where directPhragmitescontrol (e.g. cutting, herbicide) was used. Saltmarsh sparrowsAmmodramus caudacutus, which are considered globally vulnerable to extinction, were less common where tidal flow had been restored than at reference sites and nested in only one of 14 tidal‐flow restoration plots. No abundance differences were found for large wading birds, willetsTringa semipalmata, or seaside sparrowsAmmodramus maritimus. Vegetation at sites where tidal flow had been restored showed characteristics typical of lower‐elevation marsh, which is unsuitable for nesting saltmarsh sparrows. We conclude that, although tidal‐flow restorations in Connecticut controlPhragmitesand restore native saltmarsh vegetation, they produce conditions that are largely unsuitable for one of the highest conservation priority species found in easternU.S.salt marshes.

Predicting the number, orientation and spacing of dike breaches for tidal marsh restoration.

Tidal marshes are an important habitat and nursery area for fish. In the past few decades, rapid economic development in the coastal areas of China has led to the interruption and destruction of an increasing number of tidal marshes. The growing interest in tidal marsh restoration has increased the need to understand the relationship between geomorphological features and fish assemblages in the design of marsh restoration projects. We studied temporal variations in, and the effects of creek geomorphological features on, the estuarine tidal creek fish community. Using modified channel nets, we sampled fish monthly from March 2007 to February 2008 from seven tidal creeks along an intertidal channel system in Chongming Dongtan National Nature Reserve. Fourteen creek geomorphological variables were measured or derived to characterize intertidal creek geomorphological features. The Gobiidae, with 10 species, was the most speciesrich family. The most abundant fish species were Liza affinis, Chelon haematocheilus, and Lateolabrax maculatus. The fish community was dominated by juvenile marine transients, which comprised about 80% of the total catch. The highest abundance of fish occurred in June and July, and the highest biomass occurred in December. Canonical redundancy analyses demonstrated that depth, steepness, cross-sectional area, and volume significantly affected the fish species assemblage. L. affinis favored small creeks with high elevations. Synechogobius ommaturus, Acanthogobius luridus, and Carassius auratus preferred deep, steep creeks with a large cross-sectional area and volume. These findings indicate that the geomorphological features of tidal creeks should be considered in the conservation and sustainable management of fish species and in the restoration of salt marshes.

Tidal marsh restoration is an important management issue in the San Francisco Estuary (estuary). Restoration of large areas of tidal marsh is ongoing or planned in the lower estuary (up to 6,000 ha, Callaway et al. 2011). Large areas are proposed for restoration in the upper estuary under the Endangered Species Act biological opinions (3,237 ha) and the Bay Delta Conservation Plan (26,305 ha). In the lower estuary, tidal marsh has proven its value to a wide array of species that live within it (Palaima 2012). In the Sacramento–San Joaquin Delta (Delta), one important function ascribed to restoration of freshwater tidal marshes is that they make large contributions to the food web of fish in open waters (BDCP 2013). The Ecosystem Restoration Program ascribed a suite of ecological functions to tidal marsh restoration, including habitat and food web benefits to native fish (CDFW 2010). This background was the basis for a symposium, Tidal Marshes and Native Fishes in the Delta: Will Restoration Make a Difference? held at the University of California, Davis, on June 10, 2013. This paper summarizes conclusions the authors drew from the symposium.

Evaluations of tidal wetland restoration efforts suffer from a lack of appropriate reference sites and standardized methods among projects. To help address these issues, the National Estuarine Research Reserve System (NERRS) and the NOAA Restoration Center engaged in a partnership to monitor ecological responses and evaluate 17 tidal wetland restoration projects associated with five reserves. The goals of this study were to (1) determine the level of restoration achieved at each project using the restoration performance index (RPI), which compares change in parameters over time between reference and restoration sites, (2) compare hydrologic and excavation restoration projects using the RPI, (3) identify key indicator parameters for assessing restoration effectiveness, and (4) evaluate the value of the NERRS as reference sites for local restoration projects. We found that the RPI, modified for this study, was an effective tool for evaluating relative differences in restoration performance; most projects achieved an intermediate level of restoration from 2008 to 2010, and two sites became very similar to their paired reference sites, indicating that the restoration efforts were highly effective. There were no differences in RPI scores between hydrologic and excavation restoration project types. Two abiotic parameters (marsh platform elevation and groundwater level) were significantly correlated with vegetation community structure and thus can potentially influence restoration performance. Our results highlight the value of the NERRS as reference sites for assessing tidal wetland restoration projects and provide improved guidance for scientists and restoration practitioners by highlighting the RPI as a trajectory analysis tool and identifying key monitoring parameters.

A goal of wetland restoration is the establishment of resilient plant communities that persist under a variety of environmental conditions. We investigated the role of intraspecific and interspecific variation on plant community establishment in a brackish marsh that had been restored by sediment addition. Plant growth, sediment accretion, and surface elevation change in planted, not-planted, and nearby reference sites (treatments) were compared. Four perennial macrophytes were planted: Bolboschoenus robustus, Distichlis spicata, Phragmites australis, and Schoenoplectus californicus. There was 100% survival of the planted species, and all exhibited rapid vegetative spread. Intraspecific variation in stem height and cover was identified, and interspecific comparisons also indicated differences in species cover. Treatment comparisons revealed that final total cover at not-planted sites was equivalent to that at reference sites, and was highest at planted sites where P. australis became dominant. Species richness was initially highest at the reference sites, but final richness was equivalent among treatments. Soil surface elevation was greater at planted compared to not-planted and reference sites. Because of the rapid cover and increased surface elevation generated by planted species, the resiliency of restored coastal marshes may be enhanced by plantings in areas where natural colonization is slow and subsidence is high.

There are three hypothesized controls on food-chain length (FCL): energy supply (or "resource availability"), ecosystem size and disturbance (or "environmental variation"). In this article, the evidence for controls on FCL in freshwater ecosystems is evaluated. First, the various ways FCL can be measured are defined. Food-chain length typically is estimated as (1) connectance-based FCL--an average connectance between basal resources and top consumers, (2) functional FCL--by experimental determination of functionally significant effects of a top predator on lower trophic-level biomass patterns, and (3) realized FCL--an average connectance measure weighted by energy flow between basal consumers and the consumer occupying the maximum trophic position in the food web. Second, all evidence for relationships between the three hypothetical controls and FCL in freshwater ecosystems are evaluated. The review includes studies from streams, lakes, ponds, wetlands, phytotelmata, and experimental containers. Surprisingly, few studies of FCL in freshwaters that test the same suite of controls using the same methods are found. Equally compelling results arise from case studies based on functional, realized, and connectance-based measures of FCL. Third, 10 rules of thumb that could increase similarity of future studies, thereby facilitating synthesis across systems, are suggested. Fourth, it is discussed how FCL influences the concentration of contaminants in large-bodied animals (many of which are consumed by humans) as well as the efficacy of biocontrol applications in agriculture. Finally, there is a discussion of the potential relationships between global climate change, hydrology, and FCL in freshwaters.

The number of trophic transfers occurring between basal resources and top predators, food chain length (FCL), varies widely in the world's ecosystems for reasons that are poorly understood, particularly for stream ecosystems. Available evidence indicates that FCL is set by energetic constraints, environmental stochasticity, or ecosystem size effects, although no single explanation has yet accounted for FCL patterns in a broad sense. Further, whether environmental disturbance can influence FCL has been debated on both theoretical and empirical grounds for quite some time. Using data from sixteen South Island, New Zealand streams, we determined whether the so-called ecosystem size, disturbance, or resource availability hypotheses could account for FCL variation in high country fluvial environments. Stable isotope-based estimates of maximum trophic position ranged from 2.6 to 4.2 and averaged 3.5, a value on par with the global FCL average for streams. Model-selection results indicated that stream size and disturbance regime best explained across-site patterns in FCL, although resource availability was negatively correlated with our measure of disturbance; FCL approached its maximum in large, stable springs and was <3.5 trophic levels in small, fishless and/or disturbed streams. Community data indicate that size influenced FCL, primarily through its influence on local fish species richness (i.e., via trophic level additions and/or insertions), whereas disturbance did so via an effect on the relative availability of intermediate predators (i.e., predatory invertebrates) as prey for fishes. Overall, our results demonstrate that disturbance can have an important food web-structuring role in stream ecosystems, and further imply that pluralistic explanations are needed to fully understand the range of structural variation observed for real food webs.

There is an increasing demand for creation and restoration of tidal marshes around the world, as they provide highly valued ecosystem services. Yet, tidal marshes are strongly vulnerable to factors such as sea level rise and declining sediment supply. How fast the restored ecosystem develops, how resilient it is to sea level rise, and how this can be steered by restoration design, are key questions that are typically challenging to assess. In this paper, we apply a biogeomorphic model to a planned tidal marsh restoration by dike breaching. Our modeling approach integrates tidal hydrodynamics, sediment transport and vegetation dynamics, accounting for relevant fine-scale flow-vegetation interactions (less than 1 m2) and their impact on vegetation and landform development at the landscape scale (several km2) and on the long term (several decades). Our model performance is positively evaluated against observations of vegetation and geomorphic development in adjacent tidal marshes. Model scenarios demonstrate that the restored tidal marsh can keep pace with realistic rates of sea level rise and that its resilience is more sensitive to the availability of suspended sediments than to the rate of sea level rise. We further demonstrate that restoration design options can steer marsh resilience, as it affects the rates and spatial patterns of biogeomorphic development. By varying the width of two dike breaches, which serve as tidal inlets to the restored marsh, we show that a larger difference in the width of the two inlets leads to more diversity in restored habitats. This study showcases that biogeomorphic modeling can support management choices in restoration design to optimize tidal marsh development towards sustainable restoration goals.

There is an increasing demand for creation and restoration of tidal marshes around the world, as they provide highly valued ecosystem services. Yet, tidal marshes are strongly vulnerable to factors such as sea level rise and declining sediment supply. How fast the restored ecosystem develops, how resilient it is to sea level rise, and how this can be steered by restoration design, are key questions that are typically challenging to assess. In this paper, we apply a biogeomorphic model to a planned tidal marsh restoration by dike breaching. Our modeling approach integrates tidal hydrodynamics, sediment transport and vegetation dynamics, accounting for relevant fine-scale flow-vegetation interactions (less than 1 m2) and their impact on vegetation and landform development at the landscape scale (several km2) and on the long term (several decades). Our model performance is positively evaluated against observations of vegetation and geomorphic development in adjacent tidal marshes. Model scenarios demonstrate that the restored tidal marsh can keep pace with realistic rates of sea level rise and that its resilience is more sensitive to the availability of suspended sediments than to the rate of sea level rise. We further demonstrate that restoration design options can steer marsh resilience, as it affects the rates and spatial patterns of biogeomorphic development. By varying the width of two dike breaches, which serve as tidal inlets to the restored marsh, we show that a larger difference in the width of the two inlets leads to more diversity in restored habitats. This study showcases that biogeomorphic modeling can support management choices in restoration design to optimize tidal marsh development towards sustainable restoration goals.

Abstract. There is an increasing demand for the creation and restoration of tidal marshes around the world, as they provide highly valued ecosystem services. Yet restored tidal marshes are strongly vulnerable to factors such as sea level rise and declining sediment supply. How fast the restored ecosystem develops, how resilient it is to sea level rise, and how this can be steered by restoration design are key questions that are typically challenging to assess due to the complex biogeomorphic feedback processes involved. In this paper, we apply a biogeomorphic model to a specific tidal-marsh restoration project planned by dike breaching. Our modeling approach integrates tidal hydrodynamics, sediment transport, and vegetation dynamics, accounting for relevant fine-scale flow–vegetation interactions (less than 1 m2) and their impact on vegetation and landform development at the landscape scale (several km2) and in the long term (several decades). Our model performance is positively evaluated against observations of vegetation and geomorphic development in adjacent tidal marshes. Model scenarios demonstrate that the restored tidal marsh can keep pace with realistic rates of sea level rise and that its resilience is more sensitive to the availability of suspended sediments than to the rate of sea level rise. We further demonstrate that restoration design options can steer marsh resilience, as they affect the rates and spatial patterns of biogeomorphic development. By varying the width of two dike breaches, which serve as tidal inlets to the restored marsh, we show that a larger difference in the width of the two inlets leads to higher biogeomorphic diversity in restored habitats. This study showcases that biogeomorphic modeling can support management choices in restoration design to optimize tidal-marsh development towards sustainable restoration goals.

There is an increasing demand for creation and restoration of tidal marshes around the world, as they provide highly valued ecosystem services. Yet, tidal marshes are strongly vulnerable to factors such as sea level rise and declining sediment supply. How fast the restored ecosystem develops, how resilient it is to sea level rise, and how this can be steered by restoration design, are key questions that are typically challenging to assess. In this paper, we apply a biogeomorphic model to a planned tidal marsh restoration by dike breaching. Our modeling approach integrates tidal hydrodynamics, sediment transport and vegetation dynamics, accounting for relevant fine-scale flow-vegetation interactions (less than 1 m2) and their impact on vegetation and landform development at the landscape scale (several km2) and on the long term (several decades). Our model performance is positively evaluated against observations of vegetation and geomorphic development in adjacent tidal marshes. Model scenarios demonstrate that the restored tidal marsh can keep pace with realistic rates of sea level rise and that its resilience is more sensitive to the availability of suspended sediments than to the rate of sea level rise. We further demonstrate that restoration design options can steer marsh resilience, as it affects the rates and spatial patterns of biogeomorphic development. By varying the width of two dike breaches, which serve as tidal inlets to the restored marsh, we show that a larger difference in the width of the two inlets leads to more diversity in restored habitats. This study showcases that biogeomorphic modeling can support management choices in restoration design to optimize tidal marsh development towards sustainable restoration goals.

Tidal marsh restoration is becoming an increasingly common tool to plan for future sea level rise. Subsided marshes' elevation can be restored through sediment additions, which may necessitate the reestablishment of vegetation. Understanding key actions to increase vegetation cover at areas that remain persistently bare following elevation restoration is a critical component of a project's long‐term success. Dominant species can shape ecosystem function, as well as ameliorate stressful environments. We transplanted the dominant species, Salicornia pacifica, into bare areas of a restored tidal marsh in central California, United States, 3 years following a sediment addition. We tested salt hardening of plants before transplanting, targeted irrigation, transplant size, and planting configuration to identify management actions that could help vegetation persist in the most stressful areas of the high marsh. Weekly targeted irrigation until the first rains began was critical for small plant survivorship. We found that larger plants had increased survivorship and contributed higher amounts of growth and cover but did not facilitate the performance of nearby smaller plants. After 2 years, we determined that using lone, larger plants was more cost‐effective than multiple smaller plants at our tidal marsh. However, performance was highly site‐specific with dramatically less growth at a drier site with sandier soil. Our results highlight the importance of identifying site‐specific restoration strategies that either ameliorate or help plants tolerate stressful conditions, contributing to the continued success of tidal marsh restoration for climate resilience.