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IntroductionCoastal infrastructure and property, as well as intertidal wetlands, are increasingly being threatened by shoreline erosion; a consequence of human activities and climate change. Nature-based solutions, such as intertidal engineered oyster reefs, can reduce erosion and promote sediment accretion, thereby promoting the restoration and persistence of salt marshes and preventing the loss of coastal lands. Engineered oyster reef substrate and design options have rapidly expanded in the last decade, yet our understanding of how these approaches influence ecosystems and intertidal morphology is limited. Drones (or small uncrewed aerial systems [sUAS]) coupled with structure-from-motion (SfM) photogrammetry have recently been suggested as a low-cost method that offers optimal spatial coverage, fine-scale resolution, and high vertical accuracy for monitoring changes around living shorelines. MethodsWe evaluated how using different vertical and horizontal uncertainty thresholds for detection of drone-based shoreline change can influence interpretation of performance of engineered oyster reefs on coastal morphology and vegetation. We monitored three sites with engineered oyster reefs installed in 2020 and one reference site located on Carrot Island along Taylor Creek in Beaufort, NC, USA. ResultsComparisons of the Digital Elevation Models (DEMs) and orthomosaics derived from the drone imagery revealed all sites saw marsh edge retreat from 2022 to 2023 (2-3 years post-restoration), and all sites except one low-relief oyster reef site saw elevation loss. Elevation loss was highest at the control site, but marsh edge retreat was highest at one of the engineered oyster reefs. DiscussionWhile horizontal thresholds did not yield statistically different results, vertical thresholds did. Our results support using a 95% confidence interval for conservative volumetric estimates and recommend that future studies consider aligning uncertainty thresholds with monitoring goals and timelines. 

A systematic review of 20 years of studies was conducted to understand wave dissipation trends of hybrid and natural (soft) coastal features, collectively referred to as nature-based solutions (NbS). Of 13,451 studies identified and 470 studies reviewed; only 50 studies consistently reported the basic parameters required to compare wave height dissipation. These studies were used to create a basic understanding of wave dissipation across soft and hybrid features along different cross-shore widths. More specific implementation guidance for NbS is limited due to the lack of consistent monitoring practices and protocol within and between soft and hybrid features. This disparity is greatest between soft and hybrid NbS. To fully understand best practices for the wide variety of soft and hybrid NbS, more uniform monitoring data is needed to assess and more fully define wave dissipation performance. Based on the findings of this review, eight parameters to measure the wave dissipation effectiveness of NbS features are proposed. These findings will inform the development and application of evaluation protocols for future NbS projects. 

Abstract BackgroundCombined impacts from anthropogenic pressures and climate change threaten coastal ecosystems and their capacity to protect communities from hazards. One approach towards improving coastal protection is to implement “nature-based solutions” (NBS), which are actions working with nature to benefit nature and humans. Despite recent increases in global implementation of NBS projects for coastal protection, substantial gaps exist in our understanding of NBS performance. To help fill this gap, we systematically mapped the global evidence base on the ecological, physical, economic, and social performance of NBS interventions related to coastal protection. We focused on active NBS interventions, such as restoring or creating habitat, adding structure, or modifying sediment in six shallow biogenic ecosystems: salt marsh, seagrass, kelp forest, mangrove, coral reef, and shellfish reef. MethodsWe identified potentially relevant articles on the performance of NBS for coastal protection using predefined and tested search strategies across two indexing platforms, one bibliographic database, two open discovery citation indexes, one web-based search engine, and a novel literature discovery tool. We also searched 45 organizational websites for literature and solicited literature from 66 subject matter experts. Potentially relevant articles were deduplicated and then screened by title and abstract with assistance from a machine learning algorithm. Following title and abstract screening, we conducted full text screening, extracted relevant metadata into a predefined codebook, and analyzed the evidence base to determine the distribution and abundance of evidence and answer our research questions on NBS performance. ResultsOur search captured > 37,000 articles, of which 252 met our eligibility criteria for relevance to NBS performance for coastal protection and were included in the systematic map. Evidence stemmed from 31 countries and increased from the 1980s through the 2020s. Active NBS interventions for coastal protection were most often implemented in salt marshes (45%), mangrove forests (26%), and shellfish reefs (20%), whereas there were fewer NBS studies in seagrass meadows (4%), coral reefs (4%), or kelp beds (< 1%). Performance evaluations of NBS were typically conducted using observational or experimental methods at local spatial scales and over short temporal scales (< 1 year to 5 years). Evidence clusters existed for several types of NBS interventions, including restoration and addition of structures (e.g., those consisting of artificial, hybrid, or natural materials), yet evidence gaps existed for NBS interventions like alteration of invasive species. Evaluations of NBS performance commonly focused on ecological (e.g., species and population, habitat, community) and physical (e.g., waves, sediment and morphology) outcomes, whereas pronounced evidence gaps existed for economic (e.g., living standards, capital) and social (e.g., basic infrastructure, health) outcomes. ConclusionsThis systematic map highlights evidence clusters and evidence gaps related to the performance of active NBS interventions for coastal protection in shallow, biogenic ecosystems. The synthesized evidence base will help guide future research and management of NBS for coastal protection so that active interventions can be designed, sited, constructed, monitored, and adaptively managed to maximize co-benefits. Promising avenues for future research and management initiatives include implementing broad-scale spatial and temporal monitoring of NBS in multidisciplinary teams to examine not only ecological and physical outcomes but also economic and social outcomes, as well as conducting further synthesis on evidence clusters that may reveal measures of effect for specific NBS interventions. Since NBS can deliver multiple benefits, measuring a diverse suite of response variables, especially those related to ecosystem function, as well as social and economic responses, may help justify and improve societal benefits of NBS. Such an approach can help ensure that NBS can be strategically harnessed and managed to meet coastal protection goals and provide co-benefits for nature and people. 

Abstract People often modify the shoreline to mitigate erosion and protect property from storm impacts. The 2 main approaches to modification are gray infrastructure (e.g., bulkheads and seawalls) and natural or green infrastructure (NI) (e.g., living shorelines). Gray infrastructure is still more often used for coastal protection than NI, despite having more detrimental effects on ecosystem parameters, such as biodiversity. We assessed the impact of gray infrastructure on biodiversity and whether the adoption of NI can mitigate its loss. We examined the literature to quantify the relationship of gray infrastructure and NI to biodiversity and developed a model with temporal geospatial data on ecosystem distribution and shoreline modification to project future shoreline modification for our study location, coastal Georgia (United States). We applied the literature‐derived empirical relationships of infrastructure effects on biodiversity to the shoreline modification projections to predict change in biodiversity under different NI versus gray infrastructure scenarios. For our study area, which is dominated by marshes and use of gray infrastructure, when just under half of all new coastal infrastructure was to be NI, previous losses of biodiversity from gray infrastructure could be mitigated by 2100 (net change of biodiversity of +0.14%, 95% confidence interval −0.10% to +0.39%). As biodiversity continues to decline from human impacts, it is increasingly imperative to minimize negative impacts when possible. We therefore suggest policy and the permitting process be changed to promote the adoption of NI. 

Abstract BackgroundAnthropogenic pressures and climate change threaten the capacity of ecosystems to deliver a variety of services, including protecting coastal communities from hazards like flooding and erosion. Human interventions aim to buffer against or overcome these threats by providing physical protection for existing coastal infrastructure and communities, along with added ecological, social, or economic co-benefits. These interventions are a type of nature-based solution (NBS), broadly defined as actions working with nature to address societal challenges while also providing benefits for human well-being, biodiversity, and resilience. Despite the increasing popularity of NBS for coastal protection, sometimes in lieu of traditional hardened shorelines (e.g., oyster reefs instead of bulkheads), gaps remain in our understanding of whether common NBS interventions for coastal protection perform as intended. To help fill these knowledge gaps, we aim to identify, collate, and map the evidence base surrounding the performance of active NBS interventions related to coastal protection across a suite of ecological, physical, social, and economic outcomes in salt marsh, seagrass, kelp, mangrove, shellfish reef, and coral reef systems. The resulting evidence base will highlight the current knowledge on NBS performance and inform future uses of NBS meant for coastal protection. MethodsSearches for primary literature on performance of NBS for coastal protection in shallow, biogenic ecosystems will be conducted using a predefined list of indexing platforms, bibliographic databases, open discovery citation indexes, and organizational databases and websites, as well as an online search engine and novel literature discovery tool. All searches will be conducted in English and will be restricted to literature published from 1980 to present. Resulting literature will be screened against set inclusion criteria (i.e., population, intervention, outcome, study type) at the level of title and abstract followed by full text. Screening will be facilitated by a web-based active learning tool that incorporates user feedback via machine learning to prioritize articles for review. Metadata will be extracted from articles that meet inclusion criteria and summarized in a narrative report detailing the distribution and abundance of evidence surrounding NBS performance, including evidence clusters, evidence gaps, and the precision and sensitivity of the search strategy. 

Major storms can alter coastal ecosystems in several direct and indirect ways including habitat destruction, stormwater-related water quality degradation, and organism mortality. From 2010–2020, ten tropical cyclones impacted coastal North Carolina, providing an opportunity to explore ecosystem responses across multiple storms. Using monthly trawl and contemporaneous seagrass surveys conducted in Back Sound, NC, we evaluated how cyclones may affect the nursery role of shallow-water biogenic habitats by examining seagrass-associated fish responses within a temperate-subtropical estuary. We employed a general before-after-control-impact approach using trawls conducted prior (before) and subsequent (after) to storm arrival and years either without (control) or with (impact) storms. We examined whether effects were apparent over short (within ~three weeks of impact) and seasonal (May-October) timescales, as well as if the magnitude of storm-related shifts varied as a function of storm intensity. Our findings suggest that the ability of these shallow-water habitats to support juvenile fishes was not dramatically altered by hurricanes. The resilience exhibited by fishes was likely underpinned by the relative persistence of the seagrass habitat, which appeared principally undamaged by storms based upon review of available–albeit limited seagrass surveys. Increasing cyclone intensity, however, was correlated with greater declines in catch and may potentially underlie the emigration and return rate of fish after cyclones. Whether estuarine fishes will continue to be resilient to acute storm impacts despite chronic environmental degradation and predicted increases major tropical cyclone frequency and intensity remains a pressing question.