Carter. S. Smith

There is growing interest in nature‐based hybrid flood risk mitigation, in which wetland ecosystems, such as tidal marshes, are an integral part. Tidal marshes can attenuate wave loading on defense structures, reduce breach depth in case of defense structure failure, attenuate storm surges, reduce shoreline erosion, and grow vertically with sea‐level rise. Marshes are currently being restored and created for flood risk mitigation and/or for other ecosystem services, making it crucial that they can persist in the long term and therefore develop erosion‐resistant sediment beds. In this paper, we first discuss the key physical and biological processes and properties that drive the development of erosion‐resistant sediment beds in tidal marshes, showing that vegetated, consolidated sediment beds, effectively functioning food webs, and a wide intertidal zone with a variety of ecosystems are highly important for the realization of marsh restoration/creation projects for flood risk mitigation. Second, we discuss how the location (i.e., either seaward or landward of a defense structure) and the physical conditions (i.e., elevation relative to the tidal range and the strength of local wave forcing) under which tidal marsh restoration/creation takes place can determine which interventions will be most suitable. Possible interventions include: sediment nourishment, stabilization structures, managed realignment, transitional polder, regulated tidal exchange, vegetation planting/transplanting, and/or creek excavation. The location and the chosen restoration or creation intervention will strongly affect how fast marsh establishment and erosion resistance development will occur. Overall, our study reveals that successful marsh restoration/creation for nature‐based flood risk mitigation requires (1) selecting the most appropriate marsh restoration or creation intervention for a specific location, and (2) giving the marsh enough time to develop before it is needed for flood risk mitigation. The incorporation of marshes within nature‐based flood risk mitigation strategies should not only be considered at an individual site scale but also upscaled to large landscape scale consequences for flood risk mitigation, to ensure a fully functioning wider ecosystem with good connectivity between ecosystems.

Habitat edges are often considered environmentally stressful areas, and as such, research has largely focused on the impacts of physical factors in shaping these edges. However, less is known about the relative importance of biotic disturbance agents and bottom‐up drivers in shaping habitat edges. Here, we used intertidal seagrass beds as a model system to test how the independent and combined effects of stingrays—a disturbance‐generating forager in seagrass beds—and nutrient addition affect the upper elevation edge of seagrasses. A two‐season long manipulative experiment with stingray exclusion × nutrient addition revealed that shoreward seagrass edges experienced heightened loss in percent cover when exposed to stingrays ( p = 0.037) but were not impacted by nutrient additions to marine sediments ( p = 0.13). Additionally, transplant experiments designed to test whether stingrays could limit intertidal seagrass establishment in higher elevation found that transplanted seagrass had a higher chance of survival when stingrays were excluded ( p < 0.01), suggesting that seagrass could live higher in the intertidal and that stingrays may limit shoreward expansion. Finally, a multi‐site observational survey demonstrated that stingray pit abundance was a strong predictor of the distance between seagrass edge and shoreward habitats. Combined, these results challenge current understanding in plant ecology that seagrass edges are controlled mainly by physical factors and instead suggest that the structure of the seagrass shoreward edge is controlled by both physical and biotic drivers. Our results also indicate that the relative effects of consumer disturbance and physical factors in controlling edge limits are likely predicated on consumer density: in areas with higher densities of large consumers, biotic forcing is likely to be more important. Furthermore, these results could have implications for restoration in areas with high densities of disturbance‐generating foragers and align with calls for greater inclusion of animal impacts into restoration schemes. Biotic drivers along environmentally stressful edges are likely not limited to seagrasses and the generality of biotic control of habitat edges deserves further exploration across diverse ecosystems.

Living shorelines, a prevalent nature‐based coastal infrastructure technique, typically merge the restoration of coastal habitats (e.g., salt marsh, oyster reef) with gray infrastructure (e.g., rock or concrete breakwaters) to provide coastal erosion protection. With increasingly frequent and severe storms, living shorelines have been shown to effectively limit coastal erosion and loss; however, there is still uncertainty regarding the effects of living shorelines on nekton communities as compared to natural marshes and gray coastal protection strategies like bulkheads. Here, we present a dataset of living shoreline‐associated nekton species recorded over a 20‐year period in North Carolina, USA. We harmonized nekton abundance and biomass data from five different studies (each ranging in duration from 2 to 4 years) across 12 living shorelines with paired natural marshes and, in some cases, bulkheads. These studies used different gear types and sampling methodologies, and therefore future users of this dataset must carefully consider the limitations of different subsets of the data and ensure that they do not make direct catch comparisons across sites that used different methodologies. Altogether, we identified a total of 62 species groups at living shorelines, natural reference marshes, and bulkheads across three categories (i.e., crustacean, mollusk, and fish) between 2001 and 2024. We identified 49 species groups on living shorelines, 49 species groups in natural marshes, and 5 species groups on bulkheads. For each living shoreline and paired natural marsh and/or bulkhead shoreline, we report individual species counts, biomass (when available), and the sampling method. In addition, we report on the living shoreline type, age, and location. In total, these data provide vital insight into how living shorelines function as habitat for nekton, and they can be used to evaluate living shoreline effectiveness as a predominant nature‐based solution for coastal protection and biodiversity enhancement. The data are released under the Creative Commons Attribution 4.0 International License.

Many natural marine habitats are decreasing in extent despite global conservation and restoration efforts. In contrast, built marine structures, such as hardened shorelines, offshore energy and aquaculture infrastructure, and artificial reefs, are increasing in extent—and, in some locations, represent over 80% of nearshore, structured habitat. When introduced into the seascape, built marine structures inevitably interact with natural habitats, but these structures are not typically designed to support natural systems. This approach often results in overall harm to natural systems, further impeding marine conservation goals. However, there is growing recognition within the ocean management and engineering community that built marine structures can be strategically designed to minimize their negative impacts and potentially support ecosystems and associated biota. We synthesize the best available science and provide bright spot examples of how leveraging built marine structures to mimic or facilitate natural habitats can help recover biodiversity, augment ecosystem services, and rehabilitate degraded habitats, providing positive outcomes for people and nature in a changing climate. Despite these bright spots, we caution that built structures typically have overall negative environmental consequences for natural habitats and should not be used in lieu of conventional habitat restoration or conservation or to justify the destruction of natural habitats.

Ecosystems globally have reached critical tipping points because of climate change, urbanization, unsustainable resource consumption, and pollution. In response, international agreements have set targets for conserving 30% of global ecosystems and restoring 30% of degraded lands and waters by 2030 (30×30). In 2021, the United States set a target to jointly conserve and restore 30% of US lands and waters by 2030, with a specific goal to restore coastal ecosystems, namely wetlands, seagrasses, coral and oyster reefs, and mangrove and kelp forests, to increase resilience to climate change. Although US efforts to conserve and restore coastal ecosystems have increased in recent decades, critical knowledge gaps about the effectiveness of past and current efforts remain. To address key knowledge gaps, we first collated information on current and historic extent and drivers of change for wetlands, seagrasses, coral and oyster reefs, and mangrove and kelp forests in the United States. We then synthesized guiding principles from the literature for restoration practitioners to evaluate ecosystem trade‐offs, sustain and enhance ecosystem connectivity, bolster climate resilience, and promote social equity. Significant investment in standardized ecosystem mapping and monitoring and multispecies, landscape‐scale restoration efforts can improve resilience of coastal ecosystems to climate change and help the United States achieve its 30×30 target.

Background: Combined 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. Methods: We 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. Results: Our 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. Conclusions: This 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.

Predators regulate communities through top‐down control in many ecosystems. Because most studies of top‐down control last less than a year and focus on only a subset of the community, they may miss predator effects that manifest at longer timescales or across whole food webs. In southeastern US salt marshes, short‐term and small‐scale experiments indicate that nektonic predators (e.g., blue crab, fish, terrapins) facilitate the foundational grass, Spartina alterniflora, by consuming herbivorous snails and crabs. To test both how nekton affect marsh processes when the entire animal community is present, and how prior results scale over time, we conducted a 3‐year nekton exclusion experiment in a Georgia salt marsh using replicated 19.6 m² plots. Our nekton exclusions increased densities of plant‐grazing snails and juvenile deposit‐feeding fiddler crab and, in Year 2, reduced predation on tethered juvenile snails, indicating that nektonic predators control these key macroinvertebrates. However, in Year 3, densities of mesopredatory benthic mud crabs increased threefold in nekton exclusions, erasing the tethered snails' predation refuge. Nekton exclusion had no effect on Spartina biomass, likely because the observed mesopredator release suppressed grazing snail densities and elevated densities of fiddler crabs, whose burrowing alleviates soil stresses. Structural equation modeling supported the hypotheses that nektonic predators and mesopredators control invertebrate communities, with nektonic predators having stronger total effects on Spartina than mud crabs by controlling densities of species that both suppress (grazers) and facilitate (fiddler crabs) plant growth. These findings highlight that salt marshes can be resilient to multiyear reductions in nektonic predators if mesopredators are present and that multiple pathways of trophic control manifest in different ways over time to mediate community dynamics. These results highlight that larger scale and longer‐term experiments can illuminate community dynamics not previously understood, even in well‐studied ecosystems such as salt marshes.

Understanding how climate and local stressors interact is paramount for predicting future ecosystem structure. The effects of multiple stressors are often examined in small‐scale and short‐term field experiments, limiting understanding of the spatial and temporal generality of the findings. Using a 22‐year observational dataset of plant and grazer abundance in a southeastern US salt marsh, we analyzed how changes in drought and grazer density combined to affect plant biomass. We found: (1) increased drought severity and higher snail density both correlated with lower plant biomass; (2) drought and snail effects interacted additively; and, (3) snail effects had a threshold, with additive top‐down effects only occurring when snails were present at high densities. These results suggest that the emergence of multiple stressor effects can be density dependent, and they validate short‐term experimental evidence that consumers can augment environmental stress. These findings have important implications for predicting future ecosystem structure and managing natural ecosystems.

Restoring vegetation in degraded ecosystems is an increasingly common practice for promoting biodiversity and ecological function, but successful implementation is hampered by an incomplete understanding of the processes that limit restoration success. By synthesizing terrestrial and aquatic studies globally (2594 experimental tests from 610 articles), we reveal substantial herbivore control of vegetation under restoration. Herbivores at restoration sites reduced vegetation abundance more strongly (by 89%, on average) than those at relatively undegraded sites and suppressed, rather than fostered, plant diversity. These effects were particularly pronounced in regions with higher temperatures and lower precipitation. Excluding targeted herbivores temporarily or introducing their predators improved restoration by magnitudes similar to or greater than those achieved by managing plant competition or facilitation. Thus, managing herbivory is a promising strategy for enhancing vegetation restoration efforts.

Background: Anthropogenic 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.Methods: Searches 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.