Seawalls are widely constructed to protect coastal communities and infrastructure against storm surges and tidal flooding; however, they often exert significant ecological pressure on adjacent wetland ecosystems. Understanding these impacts is critical for sustainable coastal management, particularly in the context of intensifying coastal squeeze. In this study, we investigated the effects of seawall construction on benthic mollusk communities within subtropical mangrove wetlands by comparing assemblages in mangroves fronting seawalls with those in adjacent, undisturbed natural mangroves. The results showed that species richness at the plot scale did not differ significantly between the two habitats (p > 0.05), highlighting the potential limitations of relying solely on species counts for ecological assessment. Conversely, Shannon and Simpson diversity indices were significantly higher in natural mangroves. Notably, two common species of Ellobiidae were entirely absent from seawall-fronted sites despite their consistent presence in the natural reference habitats. These findings suggest that ellobiid snails may serve as effective indicator species for evaluating the ecological footprint of seawall construction. Broadly, our results underscore the necessity of incorporating multi-dimensional diversity metrics, particularly those capturing abundance distributions, alongside indicator taxa to ensure robust biodiversity assessments.

Mangrove ecosystems are vulnerable to extreme events and sea-level rise. The present study examined how biological and geomorphological processes interact at mangrove seaward margins (MSM) using remote sensing, field surveys, and elevation monitoring from 2009 to 2021 in northeastern Hainan, China. The results showed that the mangrove edge had retreated by 11.04 ± 0.36 m. Retreat was more rapid in heavily disturbed areas, especially during 2013-2017 when intense tropical cyclones occurred. In these areas, edge seedling recruitment of Rhizophora stylosa declined, with establishment probability being strongly influenced by surface elevation. Mature trees exhibited increased root damage and reduced leaf chlorophyll content, with trait variation primarily driven by surface elevation and sediment physical properties. Following vegetation dieback, surface elevation declined rapidly, forming a positive biogeomorphic feedback that further inhibited regeneration and accelerated margin degradation. We identified a feedback loop between vegetation loss and geomorphic change triggered by extreme disturbances at the MSM that limits natural recovery and threatens ecosystem stability. Our findings underscore the need to prioritize monitoring edge zones and suggest a management framework that integrates remote sensing with in situ monitoring to identify vulnerable zones and guide post-disturbance conservation and restoration under increasing environmental stress.

Major biodiversity changes in the Anthropocene demand enhanced monitoring of ecological communities. Notably, community-level attributes of coastal wetland ecosystem engineers, especially crabs (Brachyura), emerge as crucial ecological indicators. However, traditional expert-based surveys for such data remain labor-intensive, time-consuming, and often invasive. This creates an urgent need for an automated and efficient paradigm shift. We developed an RGB sensor-based automated framework and collected extensive image data from 17 coastal mangrove wetlands across China. This framework integrates expert knowledge with artificial intelligence via a pyramid-style annotation approach, utilizing optimized CNN models (YOLOv5/v8 and EfficientNet) for automated image processing and indicator extraction. Test results show that by integrating attention modules and improved anchors, our model achieved superior performance in crab detection, classification, carapace width measurement, biomass estimation, and burrow detection, matching or exceeding manual methods. It further captured plot-level spatial point patterns, addressing limitations of conventional manual surveys. Our local case study validated that image-extracted community metrics provide independent and essential insights for community analysis, offering a more efficient and comprehensive indicator system than traditional methods. Ecologically, this deep learning-integrated novel method provides an economical solution to expand the dimensionality and breadth of biological data. It enhances management effectiveness by (1) serving as foundational hardware-software for in-situ monitoring and automated data collection (scalable to other benthic fauna), and (2) capturing higher-dimensional community indicators and fine-scale spatial patterns to support biodiversity conservation, blue carbon sequestration, and vegetation protection.

In Luoyuan Bay, China, Sporobolus alterniflorus invasion has hindered mangrove restoration and disrupted faunal communities within mangrove habitats. This study investigated its impact on mollusk, crab, and fish assemblages across mangrove, mudflat, and invaded habitats from 2019 to 2020. Results showed that species diversity of three assemblages did not differ significantly between invaded and non-invaded mangrove habitats; however, assemblage structure was altered and functional traits declined markedly in invaded areas. Compared with non-invaded mangroves, invaded habitats showed decreases of 81.6% in mollusk density, 50.7% in mollusk biomass, 66.6% in crab density and 84.2% in crab biomass. Dominant fish species (Acanthogobius ommaturus, Liza carinata, Stolephorus chinensis) also exhibited lower body size, total size and biomass in invaded habitats. Given the close dependence of coastal residents on these faunal resources, a socioeconomic analysis of livelihood strategies was conducted, revealing Sinonovacula constricta aquaculture achieved the highest net income-to-investment ratio, 122.7% higher than nearshore fishery and 308.3% higher than shallow-sea oyster cultivation, while professional shellfish farming yielded the highest net income per hectare, 23.6% higher than oyster cultivation. Thus, both forms of shellfish aquaculture provide greater economic returns than other livelihood options. Based on these findings and niche theory, we propose a management framework: after removing S. alterniflorus, plant native mangroves (Kandelia obovata) in mid-to-high intertidal zones and lease lower flats for shellfish farming. This framework has the potential to integrate ecological restoration with local livelihoods and may inform similar efforts in other regions facing biological invasions and restoration challenges.

Vivipary is common in several mangrove species and is generally considered an adaptation to the intertidal saline environment. However, the coexistence of many nonviviparous mangroves makes this view controversial. This study investigated the propagule development of two nonviviparous mangrove species, Sonneratia alba and S. caseolaris, with marked differences in salt tolerance and distribution. Changes in the density, water content, and concentrations of the five main osmoregulatory elements (Cl, Na, K, Ca, and Mg) were determined. As the propagules of S. alba and S. caseolaris mature, the element concentrations (mg/g) in the propagules gradually decrease, indicating a desalination process. Moreover, the Cl, Na, Ca, and Mg content in the propagules were lower than in the mature leaves and calyx. Similar to viviparous mangroves, the development of the propagules of nonviviparous mangroves is also a desalination process. Although both viviparous and nonviviparous mangrove species undergo a desalination process during propagule development, our findings suggest that viviparity may not be solely defined by desalination, but rather by the extended period of low-salinity protection during early development on the maternal tree, which represents a key adaptation for survival in high-salinity environments. In contrast, nonviviparous mangroves, which rely on seed germination and early development in saline seawater, face additional challenges in high-salinity habitats, highlighting their distinct adaptive strategies.

Understanding biodiversity patterns across multiple taxonomic groups is crucial for effective conservation planning to address the rapid global decline in biodiversity. While mangrove plant diversity has been extensively studied, the associated fauna, particularly benthic animals, have received insufficient attention. In this study, we compiled a dataset of mangrove benthic mollusks based on field surveys, including 27,610 individuals representing 160 species across 10 natural reserves. We also included the corresponding mangrove plant species lists from field surveys and species inventories for each reserve on tropical Hainan Island, China. We analyzed the relationship between mollusk diversity and mangrove plant species richness. Results show no consistent alignment between plant and mollusk diversity, with non-significant Spearman correlation coefficients (P > 0.1). Furthermore, five out of ten sites exhibit either below-average mollusk diversity with above-average plant diversity or below-average plant diversity with above-average mollusk diversity. This suggests that plant diversity is not a reliable surrogate for mollusk diversity, and vice versa. These mismatches complicate conservation planning, as protecting a single site cannot ensure multi-taxon biodiversity. We recommend that the design of protected areas and conservation assessments include multiple taxonomic groups. In mangrove ecosystems, monitoring plant diversity alone is insufficient, and other groups, such as the mollusks examined in this study, should also be considered.

Tidal inundation is a key environmental factor in coastal wetland ecosystems, such as mangroves. Understanding the response of mangroves to increased flooding stress under rising sea levels is crucial in the context of rapid global climate change. While previous studies have focused on the mangrove seedlings in controlled experiments, field studies on the response of mature mangrove trees to rising sea levels remain limited. This study examines the impact of flooding stress caused by tidal inlet narrowing on mangroves in a tropical microtidal estuarine lagoon on Hainan Island, China. We assessed the mortality of four common mangrove species: Avicennia marina, Ceriops tagal, Rhizophora apiculata, and Scyphiphora hydrophyllacea, and conducted an elevation gradient survey of C. tagal in two transects to evaluate how different mangrove species respond to flooding stress. The average tree heights of these species were 1.79 m, 1.16 m, 3.14 m, and 2.38 m, respectively, with survival probability after the flooding event of 42%, 12%, 89%, and 95%, respectively. We found that survival probability was positively related to tree height across the four species (P < 0.001), and the site elevation of C. tagal is significantly positively associated with survival probability (P < 0.001). Additionally, higher elevations correspond to better health in surviving C. tagal, indicated by more live leaves per twig and a higher leaf Fv/Fm ratio (P < 0.001). These results suggest two mortality patterns in mangrove responses to the extreme flooding event: tree height-based and elevation-based mortality. The ordered mortality implies that mangrove vulnerability to sea- level rise is heterogeneous. These findings imply that future assessments of mangrove vulnerability should consider the fine-scale spatial distribution of species and the spatial heterogeneity of tree height.

Mangrove wetlands are naturally divided into habitat patches by tidal creeks, with patch edges highly vulnerable to human activities and biological invasions, making them critical areas for mangrove degradation. Understanding the geometrical characteristics of these patches is essential for mangrove management in the Anthropocene, yet their exploration remains limited. Using a high-resolution (2 m) mangrove distribution dataset from 2018, we analyzed the patch structure of mangroves in southern China. This study revealed predominantly small and elongated patches, with an average area of 0.044 km2 and a median of 0.011 km2 across 5857 patches. About 65% of patches had a major-axis length over twice their minor-axis length. The patch number and area peaked between 19° N and 22° N. The patch number and area peaked between 19° N and 22° N. In the 0.1° × 0.1° latitudinal-longitudinal grid, the maximum mangrove area was 9.03 km2, consisting of 192 patches. Additionally, the patch composition and geometric characteristics differed significantly among the existing reserves. These findings highlight the need to prioritize the patch geometry in management strategies, especially in regions with numerous small patches prone to degradation and invasion. Additionally, this study underscores a critical research gap: the ecological impacts of mangrove fragmentation on biodiversity and ecosystem services remain poorly understood. Future research should focus on how the patch structure and landscape configuration influence ecological processes in mangrove wetlands.

Mangrove restoration is critical for the resilience of coastal ecosystems, yet there remains insufficient research on the ecological effects of artificial versus natural restoration, especially regarding their impacts on faunal communities and ecosystem functions. This study used a space-for-time substitution approach to investigate the taxonomic and functional diversity of crab communities along a 27-year pond-to-mangrove restoration chronosequence in Dongzhaigang Bay, southern China. We analyzed temporal changes in community composition and functional traits under artificial and natural restoration approaches, compared alpha diversity and the components of beta diversity across sites, and explored the influence of environmental variables on variations in crab community structure. A total of 3,700 crabs representing 24 species were recorded. Artificial restoration sites exhibited rapid early colonization, with species richness reaching 1.5 times that of natural restoration sites by year 4. However, by year 27, both artificial and natural restoration sites showed no significant differences in crab taxonomic and functional diversity compared to natural mangroves. The results indicate that species composition in both restoration types underwent a typical successional process, beginning with dominance by filter-feeding Ocypodidae crabs in the early stages and gradually shifting to dominance by herbivorous and omnivorous crabs of the Grapsoidea family in later stages. Nevertheless, the proportion of functional groups in naturally restored sites was closer to that of natural mangroves. Soil pH and salinity were identified as the primary environmental drivers shaping both taxonomic and functional community patterns. Based on these findings, we emphasize the importance of incorporating functional traits and successional dynamics alongside taxonomic metrics to more accurately assess the ecological recovery of mangrove restoration efforts.

Afforestation of mangroves in abandoned ponds is considered an effective approach for global mangrove restoration. Although several studies have assessed recovery outcomes of reforested mangroves, the studies about the synergistic recovery of mangrove vegetation and ecosystem carbon stocks in abandoned ponds are still limited. The present study compared the vegetation structure and carbon stocks of pond-to-mangrove sites with different restored methods in Dongzhaigang Bay, Hainan Province, China. We found that the vegetation structure (tree density and Shannon diversity) had no significant differences between afforestation sites and natural mangroves. The total ecosystem carbon stocks of all the sample sites ranged from 64.07 to 224.91 (mean +/- SD: 114.82 +/- 49.30) Mg C ha(-1), while there were no significant variations between restoration sites in 2014 (p > 0.05). In addition, 85.44 % of the total carbon stocks were stored in the soil among the study sites. The soil physicochemical properties such as soil pH, total organic carbon, total nitrogen had effects on tree height, diameter at breast height and carbon stocks composition. Meanwhile, in-situ soil redox potentials, Shannon diversity, tree height, density and diameter at breast height affected carbon stock. Moreover, the soil physicochemical properties, absolute elevation and vegetation structural variables could explain 76.83 % of the carbon stock variance. This study demonstrated that artificial planting had no superiority in vegetation restoration and carbon sequestration over natural regeneration. Under appropriate environmental conditions, natural regeneration is an economically effective way to restore mangroves from abandoned ponds to realize the co-benefits of biodiversity and carbon storage restoration.

The rapid decline of mangrove ecosystems worldwide underscores the urgency of restoring these environments. In China and Southeast Asia, a recently popular method involves converting abandoned aquaculture ponds into secondary mangrove forests (i.e., pond-to-mangrove restoration), which reshapes the landscape to create suitable habitats for mangrove plants. However, an often overlooked issue is how these new habitats may facilitate the spread of exotic species. Our study examined plant communities in a pond-to-mangrove restoration area, comparing the plant community four and eight years after restoration began. We found that the exotic species Laguncularia racemosa expanded rapidly, significantly suppressing native mangrove species and altering the community structure. The relative abundance of L. racemosa increased from 8% in the fourth year to 57% by the eighth year, during which time three native species disappeared from the plot. By the eighth year, L. racemosa also dominated in terms of plant height. Given the rapid spread of invasive species and the high connectivity of wetlands, we recommend closely monitoring non-native plants during restoration projects like pond-to-mangrove restoration. Our study highlights the threat biological invasions pose to restoration efforts and the importance of managing ecological niches created by restoration processes.

Abandoned pond-to-mangrove restoration, as a more cost-effective method than mudflat afforestation, would be the primary method of mangrove restoration globally in the future. Comparing the long-term recovery and evolution characteristics of aquatic animal community assembly and key drivers across nutrient levels is essential to systematically assess the ecological benefits and effectiveness of pond-to-mangrove restoration. Here, we carried out long-term monitoring on the aquatic animal species and functional diversity recovery after abandoned ponds were converted to mangroves in China’s first pond-to-mangrove restoration area of Southern China. Co-occurrence network model and multivariate statistical analysis were used to compare the aquatic animal community assembly and key drivers across nutrient levels at different succession stages (5 years, 9 years, 28 years). We found that an increase in species and functional diversity of aquatic animals as mangrove succession in pond-to-mangrove restoration sites, but functional diversity recovery lags behind species diversity, which was dominated by changes in soil organic matter, seawater salinity, and plant traits. Greater niche width in crustacean communities caused more rapid recovery than the mollusk and fish communities. Although structural stability of aquatic animals increased, functional vulnerability increased as well owing to abiotic-driven functional redundancy decrease. Deterministic processes and stochastic processes have a disproportionate influence on the community assembly of aquatic animals, and biological stochastic processes are dominant. As mangrove succession, the stochastic process always has a higher explanation for fish, and the influence on mollusks gradually decreases, while the influence on crabs gradually increases. Our findings highlight the long-term evolution of species and functional diversity in aquatic animals and different recovery strategies across nutrient levels following the pond-to-mangrove restoration, which provide scientific evidence for the long-term biodiversity conservation and restoration of mangrove forests.

There is much controversy surrounding factors that affect the distribution of mangrove plants across the intertidal gradient. It was previously hypothesized that mangrove zonation was attributed to tidal sorting (TSH) of its propagules according to size (weight) or differential ability of propagules to establish in deep water. However, observational and experimental evidence have provided little support for the actual mechanism(s) of mangrove zonation. In general, species distribution pattern is the consequence of propagule dispersal. The specific gravity of water-borne mangrove propagules may affect their buoyancy, with inherent links to dispersal, thereby potentially influencing tree zonation. Propagule specific gravity can influence the distribution of mangroves in the context of global change, particularly in response to changes in seawater salinity. In this study, we measured the specific gravity and weight of 35 mangrove species propagules. There was no correlation between the weight of the propagule and its specific gravity. The specific gravity of propagules of true mangrove species was significantly greater than that of semi-mangrove. The results of the correlation between propagule specific gravity and the relative surface elevation of field distribution support the hypothesis that propagules are subject to tidal sorting and are not related to weight but to specific gravity. This newfound understanding of mangrove dispersal and distribution is critical in the context of mangrove protection and restoration, especially in projecting the effects of anthropogenic activities and global change on mangrove communities.

Accurately quantifying functional traits across large scales is considered fundamental for the management and conservation of existing mangrove ecosystems. In recent years, hybrid models, which combine radiative transfer model simulations with machine learning regression algorithms (MLRA), have been effectively employed in satellite-based estimations of plant functional traits across diverse ecosystems. Nevertheless, the inevitable data redundancy stemming from heavy-parameterization radiative transfer models restricts the application of the hybrid model. Previous studies have indicated that active learning (AL) strategies can mitigate this redundancy through smart sampling selection criteria. While many studies have attempted to investigate mangrove functional traits using various models, there is limited understanding of the performance of hybrid models coupled with active learning strategies in retrieving the traits. In recent years, Sentinel-2 has become mainstream for retrieving detailed and reliable information across diverse ecosystems. The aim of this study is to utilize a retrieval scheme to extract four mangrove functional traits from Sentinel-2 imagery: leaf area index (LAI), leaf chlorophyll content (Cab), leaf dry matter content (Cm), and leaf equivalent water thickness (Cw). In order to achieve this goal, we systematically evaluated 36 different MLRA-AL models, which were combinations of six MLRAs and six AL strategies. Retrieval results showed that GPR (Gaussian processes regression)-ABD (angle-based diversity) and GPR-PAL (variance-based pool of regressors) yielded the highest accuracies for LAI (R2 = 0.68, NRMSE = 10.488 %) and Cw (R2 = 0.47, NRMSE = 13.868 %), respectively. GPR-EBD (Euclidean distance-based diversity) had the highest accuracies of Cm (R2 = 0.54, NRMSE = 11.695 %) and Cab (R2 = 0.71, NRMSE = 13.764 %). The retrieval models were subsequently applied to produce distribution pattern maps of four mangrove functional traits within a Ramsar site. This study represents the first attempt to utilize AL strategies to enhance the efficiency of traditional hybrid models and map multiple functional traits of mangrove forests. The retrieval scheme and mapping results could significantly contribute to the management of mangrove ecosystems and provide a fundamental data source for future research on the ecological services of mangroves.

In recent decades, mangrove wetlands globally have suffered from human activities and climate change, leading to issues like area reduction, degraded ecological functions and declining biodiversity. Restoration efforts, primarily through mangrove afforestation (i.e. mangrove plantation in mudflats), have been widespread, yet they often overlook the significance of unvegetated mudflats. In addition, under the condition that the total area of suitable mudflats is limited, the problem of what is the threshold of mangrove forests and unvegetated mudflats to better protect mangrove biodiversity has not been solved. Therefore, this study conducted a field survey of molluscs in mangrove wetlands in Hainan Island in China and explored the relative importance of mangroves and unvegetated mudflats through taxonomic alpha diversity and functional diversity. The results showed that (1) mollusc abundance of unvegetated mudflats was notably higher than this of mangrove forests, and the species richness, functional richness and functional vulnerability were significantly lower than those of mangrove forests; (2) the abundance and functional vulnerability of molluscs were mainly affected by sediment properties (pH, interstitial water salinity, median diameter, total nitrogen, C/N ratio), while the species richness and functional richness of molluscs were primarily influenced by vegetation structure (plant density); and (3) retaining at least 20% of the unvegetated mudflat area could well protect the biodiversity of mangrove wetlands. To our knowledge, our study is the first to propose the proportion of mangrove forests and unvegetated mudflats on the basis of benthic biodiversity, providing theoretical support and decision-making reference for mangrove protection and restoration.

Coastal mangroves are strongly nutrient-limited, but a comprehensive understanding of nutrient concentration and resorption strategies in mangrove ecosystems is lacking. In this study, we measured leaf chemical stoichiometry of the mangrove species Kandelia obovata in winter (January) and summer (July) at six sites covering the latitudinal range of the species (19°N to 28°N) in China. Leaf nitrogen (N) and phosphorus (P) concentration and N:P ratio had distinct unimodal patterns along the latitudinal gradient in both seasons. Leaf N and P concentration varied seasonally, with significantly (P < 0.01) lower levels of N and P in winter than in summer at all sites. Seasonal differences were most pronounced at higher latitude sites. Nutrient resorption efficiencies (NuRE) were high in mangroves, with N resorption efficiency (NRE) consistently higher than P resorption efficiency (PRE) across all sites and seasons. The average NRE was 70.86%, whereas the average PRE was 52.73%. In contrast to variations in N and P concentration and N:P ratios, variability in NuREs and the NRE:PRE ratio was lower, with less pronounced interseason variations. Notably, NRE was significantly different in the Fugong and Leizhou sites, whereas both PRE and NRE:PRE ratios were significantly different only in the Fuding site. Among potential factors controlling nutrient resorption strategies in mangroves, the NRE:PRE ratio was significantly negatively related to green leaf N:P ratio during the summer (R2 = 0.148, P = 0.036) but was significantly positively related to sediment N:P ratio during the winter (R2 = 0.165, P = 0.026) and the merged data of two seasons (R2 = 0.071, P = 0.039). Overall, the results suggest that mangroves are strongly limited by N, and N limitation, along with nutrient stoichiometry, collectively influences nutrient resorption strategies.

Invasibility, or an ecosystem's susceptibility to invasion, plays a critical role in managing biological invasions but is challenging to quantify due to its dependence on specific ecosystem variables. This limitation restricts the practical application of this concept in the control of alien species. This study aims to simplify invasibility into measurable components and develop an applicable framework to predict early colonization of alien plants within the coastal mangrove ecosystem. We used the unchanneled path length (UPL), a widely applied hydrological connectivity-related indicator, to assess the accessibility of the mangrove. The enhanced vegetation index (EVI), positively correlated with above-ground biomass, was used to evaluate the potential competitive intensity. Firstly, building on existing studies, we developed a four-quadrant concept model integrating the effects of EVI and UPL on the early colonization of the alien species Sonneratia apetala. Our results revealed significant differences in EVI and UPL values between colonized and uncolonized areas, with colonized regions displaying markedly lower values (P < 0.001). Additionally, logistic regression showed a significant negative association between the probability of successful colonization by S. apetala and both indicators (P < 0.001). These results validate the effectiveness of our conceptual model. Furtherly, we identified four key niche opportunities for exotic species in mangrove: mudflats outside the mangrove forest, tidal creeks, canopy gaps, and unmanaged abandoned aquaculture ponds. Overall, this study provides important insight into the ecological processes of alien S. apetala colonization and practical information for management of coastal areas susceptible to invasion. Additionally, it presents a case study on the practical application of the concept of invasibility in the management of alien species.

The abandoned pond-to-mangrove restoration project provides greater advantages than tidal flats afforestation in restoring mangrove ecosystem services and will be the primary method for mangrove restoration in the future. The existing methods for abandoned pond-to-mangrove restoration include artificial restoration through 'dike-breaking, filling with imported soil and tree planting' and natural restoration through 'dike-breaking and natural succession'. However, little is known about which restoration strategy (natural or artificial restoration) provides more benefits to the biodiversity of mangrove macrobethos. Given a prevailing view suggested that artificial restoration should be the preferred approach for accelerating recovery of biodiversity and vegetation structure in tropical regions, we hypothesised higher macrobenthic biodiversity and more complex community structure in artificial restoration than in natural restoration. To test this hypothesis, macrobenthic biodiversity and ecological processes were monitored in a typical abandoned pond-to-mangrove area of Dongzhaigang Bay, China, where artificial and natural restoration methods were used concurrently. Differences in macrobenthic biodiversity, community structure and ecological processes were compared using diversity indices, complex network analysis and null models. Similar species composition and ecological niche overlap and width among macrobenthos were observed at artificial and natural restoration sites. The biotic heterogeneity and interaction among macrobenthos were higher at the natural restoration sites than at the artificial restoration sites. Macrobenthos community assembly at natural and artificial restoration sites was both determined by deterministic processes, with environmental filtering dominating, which explained 52% and 54% of the variations in macrobenthic community structures respectively. Although our findings did not validate the research hypothesis, higher biotic heterogeneity and species interaction among macrobenthos could support natural restoration as the primary method for abandoned pond-to-mangrove projects, because it is a nature-based solution for mangrove restoration.

BackgroundIn natural mangrove communities, mangrove species are often distributed zonally. Leaf-eating crabs are one of the most abundant and iconic arboreal brachyurans in mangrove forests, but variation in the composition of crab diets in different mangrove tidal zones is unknown.MethodsTo determine the contributions of mangrove leaves and other organic carbon (C) sources to leaf-eating crab diets, dual stable C and nitrogen (N) isotope signatures (δ13C and 1δ5N) were used in a Bayesian stable isotope mixing model. We conducted experiments at various tidal levels in the Dongzhaigang Bay National Natural Reserve in China. We analyzed δ13C and δ15N of leaf-eating crabs, mangrove leaves, sediment organic matter (SOM), and animal tissues (prey).ResultsThe food composition of the dominant crab species, Parasesarma continentale, exhibited significant differences among the four tidal zones. From the margin to the high tide zone, the main food source shifted from predominantly mangrove leaves and SOM to primarily SOM and animal tissues. We observed a significant negative relationship between the C/N ratios of mangrove leaves and the proportion of leaves consumed by leaf-eating crabs. Additionally, as the tidal level increased, the C/N ratio of mangrove leaves also increased, whereas the proportion of leaves consumed by crabs decreased.ConclusionLeaf-eating crab diets vary significantly across tidal zones, highlighting the importance of considering tidal zone differentiation when studying consumer diets in mangrove ecosystems.

ABSTRACT Coastal wetlands are key features of the Earth's surface and are characterized by a diverse array of coupled geomorphological and biological processes. However, the links between the distribution of biodiversity (for example, species and structural diversity) and the formation of coastal geomorphology are not well‐understood on a landscape scale most useful to coastal zone managers. This study describes the relationship between select geomorphological and biological mangrove community features (i.e. species composition and functional root type) in a landscape‐distributed coastal zone of Dongzhaigang Bay, north‐eastern Hainan Island, China. A total of 11 mangrove species and five functional aerial root types were encountered, with the location of species by root types being controlled by the elevation of the soil surface. Plank roots, prop roots and pneumatophores occupied the lowest intertidal elevations, while knee roots and fibrous roots of the mangrove fern, Acrostichum aureum , preferred the highest intertidal elevations. Surface sediment deposition in areas with mangroves was greater than deposition in non‐mangrove forest zones, establishing an important biological mechanism for this large‐area response because surface erosion/compaction was also more prominent within mangrove roots. Indeed, functional root type influenced the magnitude of deposition, erosion and compaction, with knee roots and pneumatophores being more effective in promoting deposition and preventing surface erosion/compaction than prop roots. These results indicate a potential role for vegetation type (especially functional root type) to influence coastal geomorphological processes at large landscape scales. While soil surface elevation is correlated to the distribution of mangrove species and functional root types, a significant feedback exists between elevation change and the capacity of those root types to influence coastal geomorphological differentiation within sustainable intertidal elevations. An enhanced understanding of geomorphological development, mangrove species distribution and functional root type may improve management to support nature‐based solutions that adjust more effectively to sea‐level rise through feedbacks.