An invasive species erodes the performance of coastal wetland protected areas

Macrofaunal biodiversity and trophic structure varied in response to changing environmental properties along the Spartina alterniflora invasion stages

Spartina alterniflora has significantly altered coastal ecosystems. Understanding macrofaunal responses to its invasion is crucial for managing coastal wetlands. Five invasion stages over 16 years were analyzed: no invasion, initial, young, mature, and senescing. Macrofaunal biodiversity initially increased but later declined. Environmental properties varied by stages, creating distinct habitats. The impact on macrofauna depended on species traits and invasion stage. Key species accounting for 49.54 % of dissimilarity were Stenothyra glabra, Bullacta caurina, Pseudomphala latericea, and Potamocorbula laevis. Trophic structure initially remained stable but shifted later. Organic carbon (OC), total nitrogen (TN), and C/N ratio correlated with S. alterniflora development. Height of S. alterniflora was a key environmental indicator, while OC content and C/N ratio were crucial for shaping the macrofaunal community, indicating food source changes. This study provides valuable insights for managing coastal environments.

Photic versus aphotic production of organohalogens from native versus invasive wetland plants-derived dissolved organic matter

The aphotic formation of natural organohalogens (NOHs) remains inadequately understood, in contrast to the well-documented photo-halogenation process of dissolved organic matter (DOM), despite the significant biogeochemical implications associated with NOHs. This study investigates the differences in the formation of chlorinated and brominated compounds from the photochemical and aphotic reactions of native Phragmites australis (PA-DOM) and invasive Spartina alterniflora (SA-DOM). The findings indicate that SA-DOM exhibits a greater potential for photochemical halogenation, attributed to its higher aromatic content and enhanced photostability. Utilizing advanced mass spectrometry, the study identifies nitrogen-containing and free saturated compounds as primary precursors for both types of DOM during photochemical halogenation. Notably, significant disparities in the halogenation processes of lignin/CRAM, nitrogen-containing/free saturated compounds, and amino sugars between SA-DOM and PA-DOM are observed, leading to a higher production of NOHs in PA-DOM during aphotic reactions compared to photic reactions, even in artificial seawater. Furthermore, the study emphasizes the critical role of dissolved oxygen in the formation of NOHs from PA-DOM under aphotic conditions. Given the rapid fluctuations in oxygen levels, salinity, and solar intensity, alongside tidal and diurnal cycles, the significance of both photic and aphotic pathways for NOHs formation should not be overlooked.

Climate warming increases the invasiveness of the exotic Spartina alterniflora in a coastal salt marsh: Implications for invasion management

Spartina alterniflora is a major invasive C4 grass in coastal wetlands worldwide. It spreads rapidly through both clonal growth and sexual reproduction, causing significant negative impacts on the ecological functions of coastal wetland ecosystems. A key question is whether climate warming will affect its invasiveness and how adaptive management strategies can be developed to address the anticipated climate warming. In this study, open-top chambers (OTCs) were used to elevate temperature (+1.5 °C) throughout the entire growing season for two years (2019-2020), we measured the leaf gas exchange, leaf and plant growth functional traits, as well as clonal and sexual reproduction traits of S. alterniflora under the warming and ambient (control) conditions. The results showed that (1) Compared to the control, warming significantly increased shoot biomass of S. alterniflora through both physiological and phenotypic changes in the middle and later periods of the growing season (p<0.05); (2) Warming did not affect clonal shoots (p>0.05), but it increased the shoot biomass allocation to spikes, resulting in higher spike biomass and seed production (both number and weight) compared to the control (p<0.05); (3) Warming induced alterations in seed morphology and mass distribution, leading to an increase in seed floating time (p<0.05), while the weight of the endosperm and embryo remained unaffected, and no differences in seed germination were observed (p>0.05). We concluded that climate warming affected shoot biomass through both physiological and phenotypic modifications and influenced reproductive traits by altering resource allocation to organs and seed composition. The invasiveness of S. alterniflora should increase due to increased shoot biomass, higher seed production, and longer seed floating times. Implementing cutting measures at the early flowering stage is recommended to mitigate the effects of anticipated climate warming.

The First Record of the Slaty-Breasted Rail Lewinia striata Inhabiting the Invasive Spartina alterniflora in Dafeng, Yancheng, China

In the context of the prolonged invasion of smooth cordgrass Spartina alterniflora, numerous native birds have progressively adapted to this invasive plant. Not only do certain non-specialist birds demonstrate an ability to inhabit and utilize smooth cordgrass, but a subset of specialist birds is also detected in the habitat as well. In this study, we provide evidence of the Slaty-breasted Rail Lewinia striata (Rallidae) occurring in smooth cordgrass, which had not been previously documented. These rails exhibit a significant reliance on the invaded vegetative community during their breeding season, engaging in foraging, vocalization, and even successful reproduction within the smooth cordgrass. The observations of Slaty-breasted Rail utilizing invasive smooth cordgrass highlight the possibility that, as natural wetlands continue to decline, birds that are highly dependent on marsh ecosystems may increasingly resort to the invasive Spartina community as a critical refuge. Such a transition is poised to impact their distribution, foraging, and reproduction. With the backdrop of large-scale removal of smooth cordgrass on the China coast, the disappearance of smooth cordgrass may harm the population of these birds. Further dedicated investigations and tracking of more individuals are needed to understand the specific ecological impact on Slaty-breasted Rail.

Coastal Marsh Vulnerability to Sea-Level Rise Is Exacerbated by Plant Species Invasion

Coastal salt marshes and their valuable ecosystem services are vulnerable to degradation due to rising sea levels, to which they can adapt through biogeomorphic feedbacks. However, the invasion of plant species, particularly eco-engineering species that alter these interactions, may degrade the structural integrity and functionality of salt marshes, potentially reducing their resilience to sea-level rise. Such impacts presently remain poorly understood. Focusing on coastal marshes of China, we utilized a coupled biogeomorphic model to explore the effects of Spartina alterniflora invasion versus native Suaeda salsa on coastal geomorphology, considering different sea-level rise and tidal scenarios. Our results revealed that Spartina alterniflora invasion contributed to the formation of a "levee-basin" geomorphological structure at both the landscape scale (from seaward to landward zones) and the local scale (from channel fringes to marsh interiors). This pattern led to a prominent marsh depression, particularly in "basin" areas under microtidal conditions, indicating increased vulnerability to rising sea levels in invaded systems. Additionally, the proliferation of Spartina alterniflora could completely displace Suaeda salsa. Our findings emphasize the importance of controlling plant invasion to safeguard ecosystem resilience to environmental change.

The Eurasian Magpie Preys on the Nests of Vinous-throated Parrotbills in Invasive Smooth Cordgrass

Native animals worldwide are experiencing long-term coexistence with invasive plants, leading to diverse behavioral changes. Invasive plants may create new habitat structures that affect the distribution or behavior of prey, which in turn might attract predators to these novel habitats, thereby altering predator-prey dynamics within the ecosystem. However, this phenomenon is rarely reported. Our previous research found that in the Yellow Sea wetlands of China, the native bird species, the vinous-throated parrotbill (Sinosuthora webbiana), has adapted to breeding in the invasive smooth cordgrass (Spartina alterniflora) by increasing its nesting height. Here, our observations indicate that in cordgrass habitats, the main nest predator of parrotbills was the Eurasian magpie (Pica pica), accounting for 75% of predation events. In contrast, in native habitats, the primary predators were mammals and snakes, accounting for 83% of predation events, with no nests being predated by magpies. We believe that changes in the breeding and nesting behavior of parrotbills may have attracted magpie predation in cordgrass habitats. Our findings may provide an empirical case of how behavioral changes induced by invasive plants can lead to dynamic shifts in predation relationships. We advocate for further research into this intriguing phenomenon, as it could enhance our understanding of changes in interspecific relationships and their ecological consequences within the context of biological invasions.

Ecological Effects of the Huge Invasive Species Removal Project in Coastal China

Saltmarsh wetlands are recognized as some of the most ecologically valuable yet vulnerable ecosystems globally. However, since the 1970s, saltmarsh wetlands in coastal China have been seriously threatened by the invasive Spartina alterniflora. Although the Chinese government has initiated a nationwide S. alterniflora removal project, the potential benefits and risks of this project remain unknown. Here, we focus on the Yangtze River Estuary Saltmarsh Wetland (YRESW) and simulate its future ecosystem structure, function, and quality under three scenarios based on remote sensing and field investigation data. The simulation scenarios include the absence of a removal project, natural regeneration postproject (NRP), and planted restoration postproject. The results show that the removal project will reverse the escalating invasion trend of S. alterniflora in the YRESW. Compared to the baseline year of 2022, there is a remarkable increase in ecosystem structure (composition: +107%, configuration: +27%) and ecosystem quality (+10.5%) under the NRP scenario. Although blue carbon storage sharply decreases under both scenarios involving project implementation, planted restoration can restore YRESW's carbon sequestration capacity to 0.19 Tg C per year, achieving 87% of the carbon storage present before the project. This study underscores the necessity of comprehensive and detailed risk assessments in ecological projects, particularly when dominant species are involved. Our findings hold significant implications for stabilizing coastal wetland ecosystems and promoting sustainable development in coastal areas.

Superoxide Photoproduction from Wetland Plant-Derived Dissolved Organic Matter: Implications for Biogeochemical Impacts of Plant Invasion

Although the impacts of exotic wetland plant invasions on native biodiversity, landscape features, and carbon-nitrogen cycles are well appreciated, biogeochemical consequences posed by ecological competition, such as the heterogeneity of dissolved organic matter (DOM) from plant detritus and its impact on the formation of reactive oxygen species, are poorly understood. Thus, this study delves into O2•- photogeneration potential of DOM derived from three different parts (stem, leaf, and panicle) of invasive Spartina alterniflora (SA) and native Phragmites australis (PA). It is found that DOM from the leaves of SA and the panicles of PA has a superior ability to produce O2•-. With more stable aromatic structures and a higher proportion of sulfur-containing organic compounds, SA-derived DOM generally yields more O2•- than that derived from PA. UVA exposure enhances the leaching of diverse DOM molecules from plant detritus. Based on the reported monitoring data and our findings, the invasion of SA is estimated to approximately double the concentration of O2•- in the surrounding water bodies. This study can help to predict the underlying biogeochemical impacts from the perspective of aquatic photochemistry in future scenarios of plant invasion, seawater intrusion, wetland degradation, and elevated solar UV radiation.

UAV telephotography elucidates floristic variability and beta diversity of island cliffs under grazing interventions

Cliffs contain one of the least known plant communities, which has been overlooked in biodiversity assessments due to the inherent inaccessibility. Our study adopted the unmanned aerial vehicle (UAV) with the telephoto camera to remotely clarify floristic variability across unreachable cliffs. Studied cliffs comprised 17 coastal and 13 inland cliffs in Gageodo of South Korea, among which 9 and 5 cliffs were grazed by the introduced cliff-dwelling goats. The UAV telephotography showed 154 and 166 plant species from coastal and inland cliffs, respectively. Inland cliffs contained more vascular plant species (P < 0.001), increased proportions of fern and woody species (P < 0.05), and decreased proportion of herbaceous species (P < 0.001) than coastal cliffs. It was also found that coastal and inland cliffs differed in the species composition (P < 0.001) rather than taxonomic beta diversity (P = 0.29). Furthermore, grazed coastal cliffs featured the elevated proportions of alien and annual herb species than ungrazed coastal cliffs (P < 0.05). This suggests that coastal cliffs might not be totally immune to grazing if the introduced herbivores are able to access cliff microhabitats; therefore, such anthropogenic introduction of cliff-dwelling herbivores should be excluded to conserve the native cliff plant communities.

Spartina alterniflora invasion benefits blue carbon sequestration in China

Spartina alterniflora has rapidly and extensively encroached on China's coastline over the past decades. Among the coastal areas invaded by S. alterniflora, at most 93% are mudflats. However, the effect of S. alterniflora invasion on soil organic carbon (SOC) stocks of coastal mudflats has not been systematically studied on a national scale. Here, we quantified the nationwide changes in SOC stocks in coastal mudflats associated with S. alterniflora invasion between 1990 and 2020. We found that S. alterniflora invasion significantly enhanced SOC stocks in coastal China. Nonetheless, the benefit of S. alterniflora invasion of coastal SOC stock may be weakened by continuing human intervention. We found that S. alterniflora invading mudflats added 2.3 Tg SOC stocks to China's coastal blue carbon, while 1.78 Tg SOC stocks were lost mainly due to human activities, resulted in a net SOC stock gain of 0.52 Tg C. These findings overturned the traditionally thought that S. alterniflora invasion would reduce ecosystem services by highlighting that the historical invasion of S. alterniflora has broadly and consistently enhanced blue carbon stock in coastal China.

Marine ecological security shelter in China: Concept, policy framework, mechanism and implementation obstacles

Building a marine ecological security shelter (MESS) has become the main strategy to adapt marine ecological threats in China. As China's marine policy lacks a robust framework document, it is necessary to consider whether the policy system can effectively support the construction of MESS. However, the linkage between the construction measures of MESS and related policies is not clear. Therefore, the purpose of this paper is to clarify the concept of MESS and its connection with policy, by adopting the policy content analysis method to analyze the evolution process of MESS-related policy system. The legislative shortcomings and implementation obstacles of the MESS-related policy system are then summarized and discussed. The results show that from 1981 to 2021 the MESS-related policy system has been continuously improved. However, the policy system's support and guarantee capacity for building MESS still needs to be improved. (1) Due to the lack of basic laws and special laws, the coordination among governance subjects and among policies lacks legislative guarantee. (2) The construction of MESS continues the inter-regional and inter-department administrative barriers in collaborative governance of marine environment. To establish an effective collaborative governance model, it is essential to improve the governance structure and mechanism. (3) The government-led governance pattern faces the problem of mechanism failure. The command and control instrument accounts for more than 82%, and the public and enterprises lack strong policy guarantees to participate in marine governance. (4) The policy system's adaptability to emerging threats must be improved. Marine policies rarely involve emerging threats such as climate change and new pollutants. Meanwhile, the real-time supervision and monitoring mechanism is weak. The real-time supervision is only accounting for about 10%. Generally speaking, as a complex and long-term system engineering, the construction of MESS will inevitably encounter contradictions in politics, culture, and economy. China should deepen the construction of marine ecological civilization and form a governance concept based on ecosystems. Overall, this paper helps to understand the internal connection between MESS and policy comprehensively and provides a new perspective for improving China's marine governance capacity.

Natural and regenerated saltmarshes exhibit different bulk soil and aggregate-associated organic and inorganic carbon contents but similar total carbon contents

Saltmarshes are considered to be one of the planet's most efficient carbon sinks. The continued loss of saltmarshes and induced ecological consequences promoted their restoration worldwide. Previous efforts aimed to evaluate the success of restoration in terms of organic carbon accumulation, but inorganic carbon and carbon contents within soil aggregates, which are essential for making a comprehensive assessment of the carbon sink function, were rarely studied. To fill this gap, a range of metrics including bulk and aggregate-associated soil organic and inorganic carbon contents together with the soil's physical, chemical and microbiological parameters were measured to compare natural and a 15-year restoration effort in saltmarsh habitats within the Yellow River Delta region in eastern China. The results showed that regenerated saltmarsh exhibited significantly higher soil organic carbon (SOC) contents but significantly lower soil inorganic carbon contents, resulting in no notable change in total carbon contents between the regenerated and natural saltmarshes. SOC contents within the silt and clay fractions and their contribution to the bulk SOC contents were significantly lower in the regenerated saltmarsh than those in the natural ones (P < 0.05). In regenerated saltmarsh, significantly lower soil microbial biomass and distinct microbial community composition with reduced Gram-negative to Gram-positive bacteria ratios were observed compared to natural saltmarsh. These findings indicate the stability of SOC fraction and soil microbe-mediated carbon biogeochemical processes differed between naturally occurring and artificially regenerated saltmarshes. As interest in blue carbon programs gains global attention, further research on the generation and transformation processes of different carbon fractions during restoration are needed, which can be conducive to elucidating more details in coastal carbon cycling processes.

Shorebirds-driven trophic cascade helps restore coastal wetland multifunctionality

Ecosystem restoration has traditionally focused on re-establishing vegetation and other foundation species at basal trophic levels, with mixed outcomes. Here, we show that threatened shorebirds could be important to restoring coastal wetland multifunctionality. We carried out surveys and manipulative field experiments in a region along the Yellow Sea affected by the invasive cordgrass Spartina alterniflora. We found that planting native plants alone failed to restore wetland multifunctionality in a field restoration experiment. Shorebird exclusion weakened wetland multifunctionality, whereas mimicking higher predation before shorebird population declines by excluding their key prey - crab grazers - enhanced wetland multifunctionality. The mechanism underlying these effects is a simple trophic cascade, whereby shorebirds control crab grazers that otherwise suppress native vegetation recovery and destabilize sediments (via bioturbation). Our findings suggest that harnessing the top-down effects of shorebirds - through habitat conservation, rewilding, or temporary simulation of consumptive or non-consumptive effects - should be explored as a nature-based solution to restoring the multifunctionality of degraded coastal wetlands.

TEMPERATURE AND SALINITY AFFECT DEVELOPMENT OF THE PARASITIC SEA ANEMONE EDWARDSIELLA LINEATA POTENTIALLY LIMITING ITS IMPACT AS A BIOLOGICAL CONTROL ON THE CTENOPHORE MNEMIOPSIS LEIDYI

The lined sea anemone, Edwardsiella lineata, parasitizes the ctenophore Mnemiopsis leidyi, which is one of the most destructive marine invasive species in the world. Mnemiopsis leidyi is known to tolerate a wide range of environmental conditions. However, the environmental tolerances of its most prominent parasite have never been characterized. Here we determined the effects of temperature (18, 22, 26, and 30 C) and salinity (6, 15, 24, and 33 ppt) on the survival and development of E. lineata from a vermiform parasite to a free-living polyp. At higher temperatures and lower salinities, E. lineata experienced significantly higher mortality, and it failed to develop into an adult polyp at the highest temperature (30 C) and lowest salinities we tested (6 ppt or 15 ppt). While such temperature and salinity restrictions would not currently prevent E. lineata from infecting M. leidyi in many of the European waters where it has become a destructive invasive species, these environmental limitations may be reducing overlap between host and parasite within the host's native range, a situation that could be exacerbated by climate change.

Organisms as sensors in biohybrid entities as a novel tool for in-field aquatic monitoring

Rapidly intensifying global warming and water pollution calls for more efficient and continuous environmental monitoring methods. Biohybrid systems connect mechatronic components to living organisms and this approach can be used to extract data from the organisms. Compared to conventional monitoring methods, they allow for a broader data collection over long periods, minimizing the need for sampling processes and human labour. We aim to develop a methodology for creating various bioinspired entities, here referred to as 'biohybrids', designed for long-term aquatic monitoring. Here, we test several aspects of the development of the biohybrid entity: autonomous power source, lifeform integration and partial biodegradability. An autonomous power source was supplied by microbial fuel cells which exploit electron flows from microbial metabolic processes in the sediments. Here, we show that by stacking multiple cells, sufficient power can be supplied. We integrated lifeforms into the developed bioinspired entity which includes organisms such as the zebra musselDreissena polymorphaand water fleaDaphniaspp. The setups developed allowed for observing their stress behaviours. Through this, we can monitor changes in the environment in a continuous manner. The further development of this approach will allow for extensive, long-term aquatic data collection and create an early-warning monitoring system.

Anthropogenic activities explained the difference in exotic plants invasion between protected and non-protected areas at a northern subtropics biodiversity hotspot

Biological invasion poses a major threat to biodiversity and conservation efforts in protected areas. The Greater Shennongjia Area (GSA) is one of China's 16 key areas for biodiversity, as stated in the China National Biodiversity Conservation Strategy and Action Plan. However, the local authorities lack appropriate data on the extent and impact of exotic species in protected areas, as well as lack the capacity and motivation to properly plan for exotic species strategy and action plan to support both prevention, control as well as management of exotic plants in their jurisdiction. In addition, while most previous studies have focused on exotic species in protected areas, little effort has been devoted to specifying which environmental factors contribute to the difference between protected and non-protected areas. Here, we explored the current distribution pattern of the richness and abundance of exotic species in relation to environmental variables within the GSA. In total, we found 84 exotic plant species, of which 41 exotic species within the protected areas, in 64 genera and 27 families, predominately from Asteraceae, Fabaceae, and Poaceae. The generalized linear mixed models (GLMMs) revealed that the protection status and the distance to human settlements were the most important predictors of exotic plant richness and abundance in the GSA. Our results showed that the average exotic plant richness and coverage in the protected areas were 22% and 31% lower than outside the protected areas, respectively. Such differences were probably the result of anthropogenic activities (e.g., proximity to human settlements and the proportion of cropland). Although protected areas provide an important barrier against plant invasions, invasion may be a tricky issue for protected area management in the future. The Alliance of Protected areas in Western Hubei and Eastern Chongqing will need to further consider stringent control and management strategies for the entry of exotic species into protected areas to effectively maintain the continuity and integrity of the GSA's biodiversity and ecosystems. Our results provided guidance and support to enhance the capacity of scientific and effective management and sustainable development of the Shennongjia World Natural Heritage Site and other protected areas.

Soil Water Deficit Reduced Root Hydraulic Conductivity of Common Reed (Phragmites australis)

Alterations in root hydraulics in response to varying moisture conditions remain a subject of debate. In our investigation, we subjected common reeds (Phragmites australis) to a 45-day treatment with four distinct soil moisture levels. The findings unveiled that, in response to drought stress, the total root length, surface area, volume, and average diameter exhibited varying degrees of reduction. Anatomically, drought caused a reduction in root diameter (RD), cortex thickness (CT), vessel diameter (VD), and root cross-sectional area (RCA). A decrease in soil moisture significantly reduced both whole- and single-root hydraulic conductivity (Lpwr, Lpsr). The total length, surface area, volume, and average diameter of the reed root system were significantly correlated with Lpwr, while RD, CT, and RCA were significantly correlated with Lpsr. A decrease in soil moisture content significantly influenced root morphological and anatomical characteristics, which, in turn, altered Lpr, and the transcriptome results suggest that this may be associated with the variation in the expression of abscisic acid (ABA) and aquaporins (AQPs) genes. Our initial findings address a gap in our understanding of reed hydraulics, offering fresh theoretical insights into how herbaceous plants respond to external stressors.

Invasion patterns of Spartina alterniflora: Response of clones and seedlings to flooding and salinity-A case study in the Yellow River Delta, China

The invasion of Spartina alterniflora has caused severe damage to the coastal wetland ecosystem of the Yellow River Delta, China. Flooding and salinity are key factors influencing the growth and reproduction of S. alterniflora. However, the differences in response of S. alterniflora seedlings and clonal ramets to these factors remain unclear, and it is not known how these differences affect invasion patterns. In this paper, clonal ramets and seedlings were studied separately. Through literature data integration analysis, field investigation, greenhouse experiments, and situational simulation, we demonstrated significant differences in the responses of clonal ramets and seedlings to flooding and salinity changes. Clonal ramets have no theoretical inundation duration threshold with a salinity threshold of 57 ppt (part per thousand); Seedlings have an inundation duration threshold of about 11 h/day and a salinity threshold of 43 ppt. The sensitivity of belowground indicators of two propagules-types to flooding and salinity changes was stronger than that of aboveground indicators, and it is significant for clones (P < 0.05). Clonal ramets have a larger potentially invadable area than seedlings in the Yellow River Delta. However, the actual invasion area of S. alterniflora is often limited by the responses of seedlings to flooding and salinity. In a future sea-level rise scenario, the difference in responses to flooding and salinity will cause S. alterniflora to further compress native species habitats. Our research findings can improve the efficiency and accuracy of S. alterniflora control. Management of hydrological connectivity and strict restrictions on nitrogen input to wetlands, for example, are potential new initiatives to control S. alterniflora invasion.

The importance of structural and functional characteristics of tidal channels to smooth cordgrass invasion in the Yellow River Delta, China: Implications for coastal wetland management

Understanding the spatiotemporal landscape dynamics and spread pathways of invasive plants, as well as their interactions with geomorphic landscape features, are of great importance for predicting and managing their future range-expansion in non-native habitats. Although previous studies have linked geomorphic landscape features such as tidal channels to plant invasions, the potential mechanisms and critical characteristics of tidal channels that affect the landward invasion by Spartina alterniflora, an aggressive plant in global coastal wetlands, remain unclear. Here, using high-resolution remote-sensing images of the Yellow River Delta from 2013 to 2020, we first quantified the evolution of tidal channel networks by analyzing the spatiotemporal dynamics of their structural and functional characteristics. The invasion patterns and pathways of S. alterniflora were then identified. Based on the above-mentioned quantification and identification, we finally quantified the influences of tidal channel characteristics on S. alterniflora invasion. The results showed that tidal channel networks presented increasing growth and development over time, and their spatial structure evolved from simple to complex. The external isolated expansion of S. alterniflora played a dominant role during the initial invasion stage, and then they connected the discrete patches into the meadow through marginal expansion. Afterwards, tidal channel-driven expansion gradually increased and became the primary way during the late invasion stage, accounting for about 47.3%. Notably, tidal channel networks with higher drainage efficiency (shorter OPL, higher D and E) attained larger invasion areas. The longer the tidal channels and the more sinuous the channel structure, the greater the invasion potential by S. alterniflora. These findings highlight the importance of structural and functional properties of tidal channel networks in driving plant invasion landward, which should be incorporated into future control and management of invasive plants in coastal wetlands.

Self-organized mud cracking amplifies the resilience of an iconic "Red Beach" salt marsh

Self-organized patterning, resulting from the interplay of biological and physical processes, is widespread in nature. Studies have suggested that biologically triggered self-organization can amplify ecosystem resilience. However, if purely physical forms of self-organization play a similar role remains unknown. Desiccation soil cracking is a typical physical form of self-organization in coastal salt marshes and other ecosystems. Here, we show that physically self-organized mud cracking was an important facilitating process for the establishment of seepweeds in a "Red Beach" salt marsh in China. Transient mud cracks can promote plant survivorship by trapping seeds, and enhance germination and growth by increasing water infiltration in the soil, thus facilitating the formation of a persistent salt marsh landscape. Cracks can help the salt marsh withstand more intense droughts, leading to postponed collapse and faster recovery. These are indications of enhanced resilience. Our work highlights that self-organized landscapes sculpted by physical agents can play a critical role in ecosystem dynamics and resilience to climate change.

Rapid and large changes in coastal wetland structure in China's four major river deltas

Coastal wetlands provide essential ecosystem goods and services but are extremely vulnerable to sea-level rise, extreme climate, and human activities, especially the coastal wetlands in large river deltas, which are regarded as "natural recorders" of changes in estuarine environments. In addition to the area (loss or gain) and quality (degradation or improvement) of coastal wetlands, the information on coastal wetland structure (e.g., patch size and number) are also major metrics for coastal restoration and biodiversity protection, but remain very limited in China's four major river deltas. In this study, we quantified the spatial-temporal dynamics of total area (TA) and patch number (PN) of coastal wetlands with different sizes in the four deltas and the protected areas (PAs) and assessed the effects of major driving factors during 1984-2020. We also investigated the effectiveness of PAs through the comparison of TA and PN of coastal wetlands before and after the years in which PAs were listed as Ramsar Sites. We found both TA and PN experienced substantial losses in the Liaohe River Delta and Yellow River Delta but recent recoveries in the Yangtze River Delta. The coastal wetlands had a relatively stable and variable trend in TA but had a continually increasing trend in PN in the Pearl River Delta. Furthermore, reduced coastal reclamation, ecological restoration projects, and rapid expansion of invasive plants had great impacts on the coastal wetland structure in various ways. We also found that PAs were effective in halting the decreasing trends in coastal wetland areas and slowing the expansion of reclamation, but the success of PAs is being counteracted by soaring exotic plant invasions. Our findings provide vital information for the government and the public to address increasing challenges of coastal restoration, management, and sustainability in large river deltas.

Mammalian predators and vegetated nesting habitat drive reduced protected area nesting success of Kentish plovers, Yellow Sea region, China

Protected areas provide essential habitats for wildlife by conserving natural and semi-natural habitats and reducing human disturbance. However, whether breeding birds vulnerable to nest predation can benefit from strict land management in the protected area is unclear. Here, we compare the nesting performance of two groups of a ground-nesting shorebird, the Kentish plover (Charadrius alexandrinus), in the protected area (Liaohekou Natural Reserve, hereinafter PA), and the control non-protected area (non-PA) around the Liaohekou Natural Reserve, in the north of the Yellow Sea, China, and identify which environmental factors, such as nesting habitat and nest materials, influence the daily nest survival rate (DSR). We found similar nesting habitats in both study areas, dominated by bare land or Suaeda salsa grassland. However, DSR was lower in PA (0.91 ± 0.01) than in non-PA (0.97 ± 0.01). Kentish plovers nesting in areas with vegetation cover experienced lower DSR than in bare lands in both areas, and nests built with materials of S. salsa sticks had the lowest DSR in the bare land. Data from infrared cameras confirmed relatively higher predator abundances and nest predation rates by nocturnal mammals, such as Eurasian badgers (Meles meles), in PA than in non-PA, and this pattern was especially evident for plover nests located in S. salsa grassland. Our results suggest that Liaohekou Natural Reserve protected area may not necessarily provide safe nesting sites for Kentish plovers due to the abundance of generalist mammal nest predators. However, the PA includes about 80% of the nests from both locations. This means the contribution of the total number of successful nests continues to be much higher within PA, with the benefit for the species that this brings in terms of conservation. The variation and mechanisms underlying differences in the nest predator communities of PA and non-PA deserve further study.

Effect of freshwater on plant species diversity and interspecific associations in coastal wetlands invaded by Spartina alterniflora

Plant invasions in coastal wetlands lead to the degradation of native vegetation; the introduction of freshwater in coastal wetlands would prevent the spread of invasive plants and facilitate the restoration of native vegetation. In this study, we evaluated the effects of freshwater on plant communities in the coastal wetlands of Yancheng, China, invaded by Spartina alterniflora Loisel. Two field investigations were conducted in 2008 and 2018 before and after the introduction of freshwater (started in 2011). The characteristics of plant communities were subjected to hierarchical cluster analysis and compared using several diversity indices. In addition, differences in habitat community composition and interspecific relationships of dominant species were analyzed. The results showed that S. alterniflora reduced the overall species diversity in the region. Plant species diversity increased after freshwater was introduced into the study site when compared to the areas without freshwater introduction. The introduction of freshwater caused a shift often changes in the interspecific relationships between Suaeda salsa (L.) Pall. and other species. The intensified invasion of S. alterniflora changed the interspecific relationship of native halophytes from negative to positive. Although freshwater effectively inhibited further invasion of S. alterniflora, it also increased the risk of expansion of the glycophytes in the community. The results of this study highlight the need for early intervention for restoration of coastal wetlands, preservation of biodiversity, and management of plant resources.

Long-distance facilitation of coastal ecosystem structure and resilience

“Red Beach” ecosystems along the Yellow Sea coastline are biodiversity hotspots critical for migratory shorebirds of the East Asian–Australasian Flyway. Satellite images show that these ecosystems have been shrinking markedly in recent decades. The reasons for this loss are unknown. Here, we reveal a landscape-scale biotic interaction driven by the destructive effect of invasive cordgrass on native coastal saltmarsh ecosystems that has progressively emerged over the past four decades. In contrast to previous studies showing positive effects of long-distance interactions, our study demonstrates that this negative interaction operating over 10 km is leading to the extinction of the “Red Beach” ecosystem and will dramatically impact ecosystem resilience to sea-level rise in the coming decades.

Biotic interactions that hierarchically organize ecosystems by driving ecological and evolutionary processes across spatial scales are ubiquitous in our biosphere. Biotic interactions have been extensively studied at local and global scales, but how long-distance, cross-ecosystem interactions at intermediate landscape scales influence the structure, function, and resilience of ecological systems remains poorly understood. We used remote sensing, modeling, and field data to test the hypothesis that the long-distance impact of an invasive species dramatically affects one of the largest tidal flat ecosystems in East Asia. We found that the invasion of exotic cordgrass Spartina alterniflora can produce long-distance effects on native species up to 10 km away, driving decadal coastal ecosystem transitions. The invasive cordgrass at low elevations facilitated the expansion of the native reed Phragmites australis at high elevations, leading to the massive loss and reduced resilience of the iconic Suaeda salsa “Red Beach” marshes at intermediate elevations, largely as a consequence of reduced soil salinity across the landscape. Our results illustrate the complex role that long-distance interactions can play in shaping landscape structure and ecosystem resilience and in bridging the gap between local and global biotic interactions.

An evaluating system for wetland ecological risk: Case study in coastal mainland China

Coastal wetland degradation and fragmentation contribute to habitat and biodiversity loss. We construct wetland ecological risk assessment framework to evaluate the risk posed to 35 coastal wetland national nature reserves (NNRs) in China for the years 2000 and 2020. Our wetland ecological risk index (WRI) is based on an external hazard sub-index (EHI) and an internal vulnerability sub-index. Most NNRs have low EHI values in both 2000 and 2020. Ratios of change in EHI range from -22.76% to 52.15% (a negative value indicates a decrease, a positive value an increase), and the EHI for 20 of 35 NNRs (57.1%) decreases over time. Variation in the internal vulnerability index ranges -44.78% to 88.97%, and increases at 18 NNRs (51.4%) over time. WRI variation ranges between -48.13% and 82.91%, and increases at 19 NNRs (54.3%). Most NNRs are ranked as being at low, medium risk in both 2000 and 2020. Notably, the number of high-risk NNRs increases from 3 to 10 (for which WRI values also increase). Expansion of built-up land, cropland occupation (in 2020), road disturbance, and water quality are all significantly associated WRI. Intensified management of the 10 NNRs ranked at high risk is necessary to prevent further deterioration.