Salt Marsh Species Research Articles

Species-specific and seasonal differences in the resistance of salt-marsh vegetation to wave impact

The coastal protection function provided by the vegetation of tidal wetlands (e.g. salt marshes) will play an important role in defending coastlines against storm surges in the future and depend on how these systems respond to such forcing. Extreme wave events may induce vegetation failure and thereby risking loss of functionality in coastal protection. However, crucial knowledge on how hydrodynamic forces affect salt-marsh vegetation and whether plant properties might influence plant resistance is missing. In a true-to-scale flume experiment, we exposed two salt-marsh species to extreme hydrodynamic conditions and quantified wave-induced changes in plant frontal area, which was used to estimate plant damage. Moreover, half of the plants were artificially weakened to induce senescence, thus allowing us to examine potential seasonal effects on plant resistance. Morphological, biomechanical as well as biochemical plant properties were assessed to better explain potential differences in wave-induced plant damage. Our results indicate that the plants were more robust than expected, with pioneer species Spartina anglica showing a higher resistance than the high-marsh species Elymus athericus. Furthermore, wave-induced plant damage mostly occurred in the upper part of the vegetation canopy and thus higher canopies (i.e. Elymus athericus) were more vulnerable to damage. Besides a taller canopy, Elymus athericus had weaker stems than Spartina anglica, suggesting that biomechanical properties (flexural stiffness) also played a role in defining plant resistance. Under the highest wave conditions, we also found seasonal differences in the vulnerability to plant damage but only for Elymus athericus. Although we found higher concentrations of a strengthening compound (biogenic silica) in the plant material of the weakened plants, the flexibility of the plant material was not affected indicating that the treatment might not has been applied long enough. Nevertheless, this study yields important implications since we demonstrate a high robustness of the salt-marsh vegetation as well as species-specific and seasonal differences in the vulnerability to plant damage.

Biomechanical traits of salt marsh vegetation are insensitive to future climate scenarios.

Salt marshes provide wave and flow attenuation, making them attractive for coastal protection. It is necessary to predict their coastal protection capacity in the future, when climate change will increase hydrodynamic forcing and environmental parameters such as water temperature and CO2 content. We exposed the European salt marsh species Spartina anglica and Elymus athericus to enhanced water temperature (+ 3°) and CO2 (800ppm) levels in a mesocosm experiment for 13weeks in a full factorial design. Afterwards, the effect on biomechanic vegetation traits was assessed. These traits affect the interaction of vegetation with hydrodynamic forcing, forming the basis for wave and flow attenuation. Elymus athericus did not respond to any of the treatments suggesting that it is insensitive to such future climate changes. Spartina anglica showed an increase in diameter and flexural rigidity, while Young's bending modulus and breaking force did not differ between treatments. Despite some differences between the future climate scenario and present conditions, all values lie within the natural trait ranges for the two species. Consequently, this mesocosm study suggests that the capacity of salt marshes to provide coastal protection is likely to remain constantly high and will only be affected by future changes in hydrodynamic forcing.

Studies on salt and drought tolerance of endemic and rare species in Valencian salt marshes as a tool for reintroduction programmes

Studies on salt and drought tolerance of endemic and rare species in Valencian salt marshes as a tool for reintroduction programmes

Strong Decline in Breeding-Bird Community Abundance Throughout Habitats in the Azov Region (Southeastern Ukraine) Linked to Land-Use Intensification and Climate

In recent decades, bird communities associated with agricultural systems have declined in Western and Central Europe and in North America, but how widely these dynamics extend to other regions is poorly known. In this study, we assessed the dynamics and the main drivers of the changes in the abundance, richness, and composition of breeding bird communities over a 30-year period in the various types of habitats of southeastern Ukraine (Azov region), a region that has undergone agricultural intensification for several decades. This study was conducted in the valley of the Molochna River during the 1988 to 2018 nesting seasons. The area studied hosted 81 bird species. Species richness varied from three species in salt marshes to thirty-three in reed beds but did not show a general trend over time. However, we identified a decline in bird communities’ total abundance over time in all habitats except shelterbelts and meadows. Similarly, species composition changed over time, reflecting the way in which species varied in their abundance changes. Climatic variables contributed to bird community turnover, but with decreasing importance over time. Overall, our results indicate that the recent declines in bird populations in farmland regions also extend to eastern Europe, with land-use effects interacting with climate to shape temporal dynamics of bird communities.

Tracking annual changes in the distribution and composition of saltmarsh vegetation on the Jiangsu coast of China using Landsat time series–based phenological parameters

Saltmarshes provide among the most valuable ecosystem services but have undergone continuous modification under the combined pressures of climate change and anthropogenic disturbance. Dynamic monitoring of the distribution and composition of saltmarsh vegetation is an urgent need for understanding the balance of saltmarshes. Previous studies have examined the possibility of identifying the plant species of saltmarshes using Land Surface Phenology (LSP). However, balancing species identification with the timespan of the monitoring remains challenging, given that the available observations are limited by the frequent occurrence of cloudy weather and periodic tidal fluctuations in coastal areas. To overcome the difficulty, we first filtered out observations contaminated by cloud cover and tidal flooding, then proposed an intra-annual time-series model by incorporating inter-annual observations using the inter-calibrated Landsat observations, finally classified the plant species of saltmarshes using phenological parameters derived from the intra-annual time-series model. The annual changes of the three dominant plant species—Spartina alterniflora (S. alterniflora), Suaeda salsa (S. salsa), and Phragmites australis (P. australis) during 2000–2020 in Jiangsu Province, the most abundant salt marsh area of China, were tracked. The results demonstrate the following: (i) The intrinsic phenological differences among the plant species (∼32 days between S. alterniflora and P. australis) are greater than the latitudinal and temporal phenological variations (9–24 days). Large-scale and long-term classification mapping using LSP was thus feasible. (ii) The annual classification maps achieved a favorable performance with an average overall accuracy of 84.8% with minor fluctuations of 5.5%. Sufficient available observations for the spring and autumn seasons (R2 = 0.78, p < 0.05) and for locations far from the sea (>240 m) were the reasons for this good performance. (iii) The saltmarsh vegetation was resilient to tidal flat reclamation on the Jiangsu coast, as indicated by a slight increase in the area from 300.30 to 336.38 km2. However, this was concentrated within the Nature Reserve (38.3%), with the increasing dominance of two species: S. alterniflora (49.6%) and P. australis (42.7%). Special conservation measures are needed for S. salsa to prevent its continuing decrease and possible future disappearance.

Pinpointing stage‐specific causes of recruitment bottlenecks to optimize seed‐based wetland restoration

Abstract Attaining the goals of ‘The UN‐Decade on Ecosystem Restoration’ requires efficient methods for large‐scale restoration of degraded ecosystems. Seed‐based approaches may offer opportunities for massive recovery of native vegetation but are prone to failure when applied to highly valued coastal wetlands such as salt marshes. Pinpointing the impact of early life stage transitions on recruitment variation across species and contexts is a critical first step toward amplifying seed‐based restoration efficiency. Large‐scale field experiments were conducted in 100 microhabitats across eight salt marshes to investigate root causes of variation in seed retention and seedling emergence, using four globally occurring salt marsh species as models. The resulting insights and dataset were then translated into predictors using machine learning, for targeted application in disentangling recruitment bottlenecks. Seed retention, regardless of species, was identified as the principal bottleneck in recruitment with hydrodynamic intensity, bed‐level dynamics, and burial depth as critical governing factors. Seedling emergence was discerned as the critical bottleneck driving cross‐species recruitment variability and was pivotally influenced by soil salinity and burial depth. Predictions using machine learning under different restoration scenarios indicated that simple management, such as seed burial or species selection, can create opportunities to bypass potential recruitment bottlenecks. Synthesis and applications. Our results suggest that the failure of seed‐based coastal wetland restoration should be attributed to multiple recruitment bottlenecks that arise from different life stage transitions and are context/species dependent. In planning future seed‐based restoration practices, managers should assess the variability of life stage‐specific dominant factors at target sites to identify site‐specific recruitment bottleneck(s). Our work underscores the need for strategic management that buffers against recruitment bottlenecks to improve restoration efficiency and advances the application of data‐driven techniques to make seed‐based restoration predictive.

Modelling the morphological response of the Oka estuary (SE Bay of Biscay) to climate change

Adaptation in and around estuaries, to ensure the future resilience of both the natural environment and the communities that are located alongside is an increasingly pressing need. As part of an adaptation planning program for the Basque estuaries (northern Spain, south-eastern Bay of Biscay), a modelling system to simulate the morphological response of the Oka estuary to climate change has been developed. Existing knowledge was used as the basis to frame this pilot modelling examining both the short-term change (storm, seasonal, annual) and the longer-term changes (decades to eons). In this paper, we focus on the long-term response and consideration of the output from the process model is limited to the data that was extracted to help parameterize the long-term model. The latter was then used to examine the response of the estuary to the past changes over a historical time scale, where observations from foraminiferal analysis and saltmarsh response were used to establish the predictive validity of the model.Forcing the model with a linear rate of sea level rise representative of the 20th century, the estuary keeps pace with sea level rise in agreement with the observations. An 18.6-year periodic variability was identified over the saltmarshes, by including the effect of the nodal tide, with the last deposition maximum occurring in 2020.The effect of the opening of a saltmarsh that was drained at the beginning of the 18th century was investigated using a simplified schematization and showed sedimentation rates of up to one order of magnitude larger than in natural marsh, in general agreement with the rates obtained in previous studies.To predict the future response of the estuary, simulations with an exponential sea level rise were performed using scenarios obtained from the latest IPCC projections. The estuary fails to keep pace with sea level rise in any of the scenarios considered. The attendant increase in the hydroperiod over the saltmarshes is also likely impact to saltmarsh species productivity and distribution.Despite the simplifications inherent to the model, and the simplifications made in the representation of the estuary and forcing conditions, the methods presented here provide additional insights into long-term behaviour that complement information obtained from more detailed, but short-term, process models. The combined modelling approach allows adaptation measures to climate change to be considered over longer timescales.

Microbial Composition of Freshwater Marsh Sediment Responds more Strongly to Microcosm Seawater Addition than Simulated Nitrate or Phosphate Eutrophication.

As sea level rise impacts coastal wetlands, saltmarsh will overtake coastal freshwater marsh in many areas, but changes in the sediment microbiome in response to saltwater intrusion are difficult to predict. Coastal freshwater marsh sediment was exposed to ambient, brackish, and saline conditions as well as to elevated nitrate and phosphate to model the combined stresses of saltwater intrusion and coastal eutrophication. Initially, sediment prokaryotic composition was similar to prior studies of freshwater marsh but diverged over time, reflecting the magnitude of increase in saltwater. There was no observed effect of nutrient amendment, potentially ranking seawater intrusion as a higher-importance compositional driver. Although the previously described loss of methanogenic populations and promotion of sulfate reducers in response to saltwater exposure was observed, taxonomic distribution was not similar to typical meso-polyhaline wetlands. Without colonization by marine taxa, such a community may be short-lived naturally, ultimately equilibrating with more common saltmarsh species. However, the recapitulation of salinity concentration by freshwater sediment microbial composition demonstrates the overwhelming nature of saltwater intrusion relative to other drivers like eutrophication.

Role of saltmarsh systems in estuarine trapping of microplastics

Saltmarshes are important natural ecosystems along many temperate (and other) coastlines. They stabilize sediments and act as biofilters for a range of industrial pollutants and, potentially, microplastics. Accumulation of microplastics along estuarine coastlines may be enhanced by the presence of saltmarsh species, as they offer better particle trapping efficiency than adjacent intertidal mudflats under prevailing flood and ebb tidal currents. However, the trapping efficiency of entire saltmarsh systems under varying flow conditions has not been widely assessed. While the effects of saltmarsh systems on water flow, and on sediment transport and trapping, have been relatively well studied, little is known about the contributions of saltmarsh halophytes, resident organisms and the associated saltmarsh sediments to the trapping of microplastics. To address this, a series of flume experiments were undertaken to examine transport and accumulation of Bakelite particles (~ 500 µm) and PVC nurdles (~ 5 mm) as model plastics in sub-sampled saltmarsh and intertidal mudflat monoliths. The results showed that saltmarsh systems influenced the hydrodynamics within and above the canopy, enhancing turbulence and shear stresses. With increasing flow velocities (≤ 0.51 m s−1), negligible quantities (2 times 10−4 mg L−1) of sediments and Bakelite particles were eroded and resuspended. The algal biogenic roughness from the mudflat, and the vegetative roughness from the Spartina plants on the saltmarsh, inhibited the transportation of the microplastics within the tested systems. Resident burrowing crabs (Carcinus maenas) promoted the burial, release and transport of microplastics. The results of this study provide evidence of the contributory roles of saltmarsh systems in the sequestration of microplastics and sediment stabilization. Estuarine saltmarsh systems can act as sinks for microplastics with enhanced burial from burrowing crabs under favourable flow conditions.

Innovative tidal control successfully promotes saltmarsh restoration

The reduction of saltmarsh habitat at a global scale has seen a concomitant loss of associated ecosystem services. As such, there is a need and a push for habitat rehabilitation. This study examined an innovative saltmarsh restoration project in Australia which sought to address the threats of mangrove encroachment and sea level rise. The project was implemented in 2017, using automated hydraulic control gates, termed “SmartGates,” to lower the tidal regime over one site, effectively reversing sea level rise at a local level. Measured indicators of saltmarsh cover, number of species, seedling counts, and saltmarsh assemblages all showed significant positive development over time, with trends varying based on saltmarsh zone. The saltmarsh, predominantly Sarcocornia quinqueflora, developed from remnant supralittoral (previously high) marsh which remained at 45% cover to achieve over 15% coverage across the cleared habitat after 3 years. Slower development in the low marsh (&lt;5%) compared to other zones contrasts with other saltmarsh restoration studies which may be due to the unique nature of the restoration method or the nature of Australian saltmarsh species which favor higher elevations and drier conditions. The development of saltmarsh at the treatment site was found to track toward that at comparison sites over time, becoming similar to some comparison sites by the studies end. This study highlights the usefulness of the novel restoration method used and of the measured indicators for assessing saltmarsh development. This innovative tidal control method could play an important role in the future of saltmarsh restoration worldwide.

Hindcast-validated species distribution models reveal future vulnerabilities of mangroves and salt marsh species.

Rapid climate change is threatening biodiversity via habitat loss, range shifts, increases in invasive species, novel species interactions, and other unforeseen changes. Coastal and estuarine species are especially vulnerable to the impacts of climate change due to sea level rise and may be severely impacted in the next several decades. Species distribution modeling can project the potential future distributions of species under scenarios of climate change using bioclimatic data and georeferenced occurrence data. However, models projecting suitable habitat into the future are impossible to ground truth. One solution is to develop species distribution models for the present and project them to periods in the recent past where distributions are known to test model performance before making projections into the future. Here, we develop models using abiotic environmental variables to quantify the current suitable habitat available to eight Neotropical coastal species: four mangrove species and four salt marsh species. Using a novel model validation approach that leverages newly available monthly climatic data from 1960 to 2018, we project these niche models into two time periods in the recent past (i.e., within the past half century) when either mangrove or salt marsh dominance was documented via other data sources. Models were hindcast‐validated and then used to project the suitable habitat of all species at four time periods in the future under a model of climate change. For all future time periods, the projected suitable habitat of mangrove species decreased, and suitable habitat declined more severely in salt marsh species.

A paradigm shift in the quantification of wave energy attenuation due to saltmarshes based on their standing biomass

Most existing analytical and numerical models to quantify wave energy attenuation attributed to saltmarshes are based on the definition of a drag coefficient that varies with vegetation and wave characteristics and requires calibration, i.e., a case-specific variable. With the aim of determining a new variable to estimate wave energy attenuation without the use of calibration coefficients, wave attenuation caused by different saltmarsh species and the relationship with the ecosystem standing biomass are experimentally studied. Samples of four real saltmarshes with contrasting morphological and biomechanical properties, namely, Spartina sp., Salicornia sp., Halimione sp. and Juncus sp., are collected in the field and placed in a wave flume for testing under different regular and random wave conditions. Two meadow densities are considered, in addition to zero-density cases. Thus, wave damping coefficients are obtained in vegetated cases, β, and bare soil cases, βB, and wave damping produced solely by the meadow standing biomass, βSB, is determined. The obtained wave damping coefficients are related to a new variable, the hydraulic standing biomass (HSB), which is defined as a function of the meadow mean height and standing biomass and incident flow characteristics. Linear fitting relationships between the wave damping coefficient and HSB are obtained, allowing β and βSB estimation without the need for calibration. Therefore, the use of these new relationships facilitates direct quantification of wave energy attenuation due to saltmarshes based on incident wave conditions, mean plant height and meadow standing biomass, variables that can be obtained from aerial images or remote sensing data, extending the applicability of the approach. Another key aspect is that this approach does not depend on any calibration coefficient and can be directly applied with knowledge of the abovementioned characteristics. This may represent a paradigm shift in the estimation of wave energy attenuation attributed to saltmarshes.

Habitat selection in Many-colored Rush Tyrant (Tachuris rubrigastra) and Wren-like Rushbird (Phleocryptes melanops) in the subtropical salt marshes of Brazil

ABSTRACT The Many-colored Rush Tyrant (Tachuris rubrigastra) and Wren-like Rushbird (Phleocryptes melanops) are birds that inhabit the subtropical salt marshes of Brazil, a newly recognized ecosystem of tidal marshes. We studied the habitat selection of these species in the subtropical salt marshes, characterizing the vegetation types where the species did and did not occur in the same habitats. The species occurred in a total of four very simplified vegetation types, characterized by the dominance of one or two plant species, including Schoenoplectus californicus, Crinum americanum, Cladium jamaicense, and Typha domingensis. We found that the habitats selected by the birds have very specific phytophysiognomic characteristics related to vegetation height and density. Moreover, the lower altitudes of certain areas of occurrence implies longer and higher flooding during periods of high tides; thus, the greater height of the vegetation maintains an above-water-level foraging and protective area for the birds. The fact that subtropical salt marshes are a transitional ecosystem suggests the possibility of rapid changes in plant succession or an intensification of the tropicalization process with mangrove expansion, which could eliminate habitat characteristics that are crucial to the survival of these two bird species in the subtropical salt marshes of Brazil.

Plant traits affect vertical accretion of salt marshes

The current climate crisis is associated with rising sea levels, which raises the concerning prospect of losing coastal ecosystems, such as salt marshes. Where inland migration is impossible, salt marshes will only persist if their vertical accretion exceeds the rate of sea-level rise. Positive vertical accretion is mainly driven by sedimentation, whereas negative vertical accretion is driven by erosion and soil compaction, among others. These processes can be influenced by abiotic and biotic factors. The biotic factors, best described by plant functional traits of the salt-marsh vegetation, are, however, not well understood. We assembled a large dataset of 336 plots with vertical accretion time series and plant abundances and coupled it with trait data from salt marsh species of the German Wadden Sea, covering natural unmanaged, anthropogenic unmanaged, and grazed marshes. By using multiple logistic regression analyses, we studied the effects of plant functional traits and distance to the marsh edge on vertical accretion. Mean vertical accretion was in the range of recent sea level rise, except for plots on elevated grazed marshes. There were, however, pronounced local differences in vertical accretion. Positive accretion increased with distance to marsh edge and increasing leaf and stem roughness, described by specific stem length, canopy height, stem mass, leaf mass and leaf area. Except on grazed marshes, leaf traits contributed more strongly to the explanation of positive accretion than stem traits. Negative accretion by e.g., erosion was facilitated by low specific root length and low root and rhizome mass, i.e., lower anchoring capacity. To better assess coastal resilience to sea level rise, our findings suggest (i) to include these effect traits in models and experimental analyses of salt marsh vertical accretion and (ii) to consider effects of vegetation roughness on accretion in salt marsh management schemes.

Unraveling the wheel of recruitment for salt-marsh seedlings: Resistance to and recovery after dislodgement

Elucidating bottlenecks at critical life stages and quantifying associated resilience (including resistance and recovery) to physical processes are central in inform restoration and attain sustainable development of coastal biogeomorphic ecosystems. Seedling establishment is a key life stage determines saltmarsh restoration potentials. However, the resilience of these recruits, especially through recovery, remains poorly understood. Here, two contrasting globally occurring saltmarsh species, namely Salicornia europaea and Spartina anglica, were employed to generate insights in i) seedling resistance against dislodgement, and ii) seedling recovery potential after dislodgement. Regarding resistance, we found that 1) root-shoot antagonism characterizes the growth rate of seedling resistance to dislodgement through hydraulic disturbance, 2) the root length determines seedling resistance to dislodgement through sheet erosion; 3) a 5 mm sedimentary setting amplifies seedling resistance without inhibiting their morphological evolution. Regarding recovery, we found that 4) dislodged seedlings have a high probability for achieving long-distance dispersal; 5) seedling age and the inundation-free period regulate the re-establishment potential of dislodged seedlings. Overall, S. anglica showed stronger resilience than S. europaea, characterized by stronger seedling resistance against dislodgement and higher re-establishment potential. Our results on seedling resilience suggest that seedling dislodgement is not an end-of-life cycle but a new spin on the “Wheel of Recruitment”, a proposed short-term cyclic behavior with alternating phases of seedling dislodgement, dispersal, and (re-)establishment. The Wheel of Recruitment concept is important for forecasting resilience and persistence of biogeomorphic systems such as salt marshes under global change and for guiding life cycle informed restoration.

Coastal Wetland Soil Carbon Storage at Mangrove Range Limits in Apalachicola Bay, FL: Observations and Expectations

Globally, mangrove range limits are expanding, often at the cost of adjacent coastal ecosystems including saltmarshes, potentially leading to a change in ecosystem services such as organic carbon (OC) sequestration. Studies in the southeastern US have focused almost exclusively onAvicennia germinansrange expansion, the most cold-tolerant mangroves in North America. The Apalachicola Bay region of north Florida represents the northern range limit of mangroves in the Gulf of Mexico, and uniquely also includesRhizophora mangle. The objective of this research was to quantify soil OC density beneath both mangrove species and compare results to the soils beneath two contiguous native tidal saltmarsh species:Juncus roemerianusandSpartina alterniflorain a barrier island setting. Dominant plant taxa were not a significant predictor of soil OC density, highlighting the relative importance of site-specific environmental attributes as controls on soil properties. Soil profile δ13C compositions included a range of values reflective of C3and C4plant inputs, suggesting that shifts in plant taxa, both from marsh to mangroves and between marsh species, have been occurring at all sites in this study. These findings support much of the literature on mangrove encroachment, which indicates mangrove soil OC concentrations, densities, or stocks are less than or equal to that of co-located tidal marsh habitats. Through a systematic review, the potential of several proposed explanatory variables (climate, environmental setting, plant physiology and productivity, and duration of encroachment) were identified to evaluate how soil OC density in mangrove habitats might increase over time, which is critical to forecasting how continued mangrove expansion might affect blue C storage as these habitats evolve.

Assessment of Biodiversity and Blue Carbon in Mangroves, Sea grasses, Salt Marshes and Algae in Mannar, Northern Sri Lanka

Blue carbon is the carbon stored in coastal and marine ecosystems. Coastal ecosystems such as mangroves, tidal marshes, seagrass meadows and algae sequester and store more carbon per unit area than terrestrial forests and are now being recognised for their role in mitigating climate change. The objective of this study was to assess the biodiversity and carbon storage capacities in these ecosystems. The study was conducted in Vidathalathivu in Mannar, Kiranchi in Kilinochchi and Pooneryn. In mangroves, belt transects were taken from the shore towards the land. Nested circular plots having 7 m radius were established, large trees were sampled for diameter. Small trees (&lt;3 cm dbh) were sampled in 2 m radius. Litter, pneumatophores and seedlings were sampled in plots of 30×30 cm area. Soil samples were taken at depths; 0-30 cm, 30-60 cm, 60-100 cm for the measurement of bulk density and carbon content. The biomass of the mangrove plants was measured using species specific allometric equations. In the salt marshes, 1×1 m plots were sampled. In the seagrass beds and algae, several 30×30 cm grids were sampled. In each plot, the species composition and the number of plants in each species were assessed. Samples of seagrasses and salt marsh vegetation were uprooted and taken to the laboratory for oven dry analysis. Three soil cores were taken using the soil auger which was inserted to a depth of 1 m in each ecosystem. The soil samples were taken from the core to represent the following depths; 0-30 and 30-60, 60-90. The data was analysed using MINITAB statistical software. The results showed natural mangroves in the study sites comprised of Avicennia marina, Ceriops tagal, Excoecaria agallocha, Luminetzera racemosa, Rhizophora murconata and Pemphis acidula. In sea grasses, Thalassima hemprichii, Cymodocea serrulate, Ruppia maritima and Syringodium isoiifolium were observed. Kappaphycus alvarezii and Eucheuma spinosum were the cultivated algae and Padina antillarum, Caulerpa racemosa, Ulva lactuca, Sargassum illifolium and Gelidium sp. were natural ones observed. Suaeda sp. and Salicornia sp. were the salt marsh species observed. The carbon content of these ecosystems were assessed. Keywords: Blue carbon, Mangroves, Seagrasses, Salt marshes, Algae, Carbon sequestration

Drainage-Improved Sediment Strength Enhances Saltmarsh Seedling Establishment Chance

Identify critical factors driving seedling establishment is essential for saltmarsh restoration. Recent studies highlight drainage can facilitate seedling establishment for different saltmarsh species, yet the underling mechanism remains largely unknown. By a manipulative mesocosm experiment with contrasting sediment drainage treatments, we investigated the impacts of drainage onSpartina anglicaseedlings survival, growth and stability. Surprisingly, neitherS. anglicaseedling survival nor seedling growth were observed to be directly promoted by well drained treatment. However, the critical erosion depth (maximum erosion tolerance) ofS. anglicaseedlings was found to positively correlate with seedling root length. Measurements on the sediment properties revealed that drainage increased the critical shear strength of sediments with lower water content and higher dry bulk density. These findings indicate that, by dewatering, drainage aids to sediment consolidation and critical shear strength, and thereby facilitate seedling establishment in tempering sediment dynamics. The latter is supported by a field study, in which we found that the magnitude of the sediment dynamics on two tidal flats were positively related to water content of sediment. Overall, present study suggests that drainage could be a key factor that determines seedling stability during the critical windows of opportunity for seedling establishment, and that it could be integrated into future designs for saltmarsh restoration to enhance establishment success.

Building spectral catalogue for salt marsh vegetation, hyperspectral and multispectral remote sensing

Salt marshes are coastal wetlands dominated by the grasslands and they are one among the most productive coastal ecosystems which provide several benefits and multiple ecosystem services. Their spatial distribution is at risk due to wide range of human activities and sea level rise. Remote sensing technique can be applied to assess their spatial coverage in quick time. Field spectrometry, an accessory tool of remote sensing, measures the reflectance using spectroradiometer to acquire continuous spectrum from a target. Developing spectral catalogue for salt marsh vegetation is essential to discriminate the vegetation into species level. In the present study, species canopy spectral signatures for seven salt marsh species were measured using spectroradiometer. Several post-processing steps were conducted for noise removal and the spectral catalogue was developed. In addition, Landuse/Landcover (LULC) spectral signatures for salt marsh vegetation were acquired from Multispectral data ofSentinel-2B satellite in near real-time using field ground truth coordinates. The species canopy and LULC spectral signatures were applied in the MSI data to perform species level classification of salt marsh vegetation. The results were significant, and indicated an overall accuracy of 65.8%, and 73.55% for species canopy and LULC spectral signatures respectively. The spectral outcome of this study can be utilized directly for rapid classification and to assess the change in the dynamics of salt marsh ecosystems for the areas with low accessibility. Further the mapping results can be used as baseline information for change detection analysis which would support coastal resources management, and help in strengthening the regulatory framework for protection and conservation purposes.

Temporal and spatial patterns of airborne pollen dispersal in six salt marsh halophytes

Pollination is a key process in the life cycle of most plant species, but very little is known about airborne pollen dispersal in salt marsh anemophilous halophytes. We analyzed the temporal and spatial dynamics of airborne pollen dispersal, using portable volumetric pollen traps, for six anemophilous Chenopodiaceae halophytic species in tidal salt marshes. In addition, we studied the effects of air temperature and wind speed on airborne pollen dispersal. Our study shows high levels of temporal and spatial constraint on airborne pollen dispersal. We recorded the lowest airborne pollen concentrations at air temperatures lower than 22 °C and wind speeds higher than 6 m s−1. These environmental conditions set up a narrow temporal pollination window during morning hours. We also recorded severe spatial limitation for pollen dispersal in three of the six halophytes studied, which presented airborne pollen concentrations that were 9 to 53 times smaller only 5 m away from source populations than within those populations. These results show that even related species colonizing the same ecosystem may show contrasted airborne pollen spatial dispersal dynamics that depend on several environmental factors. This should be taken into account for estimates of vegetation composition based on pollen production in aerobiological and paleopalinological studies. The restricted airborne pollen dispersal recorded would promote geitonogamy and limit interpopulation genetic exchange to the dispersal of their hydrochorous fruits.