Salt Marsh Habitats Research Articles

Impacts of Climate Change on Mycorrhizal Fungi in Salt Marsh Habitats

Salt marshes are coastal wetlands that cover 2-3% of land surface area.1 These habitats carry out several essential functions such as providing habitats for many species, acting as a buffer between terrestrial land and ocean waters, and most importantly, acting as a major carbon (C) storage pool. Arbuscular mycorrhizal fungal (AMF) symbionts are key organisms in salt marsh habitats and are known to influence the following: plant zonation, plant resource competition, plant productivity, plant genetic diversity, soil C sequestration, soil C:N:P ratios, saprotrophic bacterial population and diversity, soil stability, and litter decomposition. Under rapidly changing conditions caused by climate change it is difficult to predict how AMF communities will respond to these factors, which would ultimately alter those processes. In this review, we will outline the functions and roles that AMF communities play in salt marsh soils. Additionally, we will present current knowledge and predictions of how AMF will respond to rising sea levels, elevated CO₂ levels, and eutrophication. Lastly, we will outline our research design and methods which aims to identify soil fungal diversity and abundance in different grass patches. We will also look at several factors that potentially alter soil fungi such as edge-effects, elevation gradients, patch size, soil conductivity, pH, and soil stoichiometry. Studying soil fungi is essential for understanding how these communities are predicted to react to a changing climate, and consequently alter salt marsh processes.

Spatio-temporal patterns in stable isotope composition of a benthic intertidal food web reveal limited influence from salt marsh vegetation and green tide

Assessing fluxes of matter and energy in food webs within and across benthic habitats is important to understand the ecological functioning in bays and estuaries, where the productivity is favoured by a wide diversity of primary producers. The temporal variability (March vs September 2019) in the carbon and nitrogen stable isotope composition of primary food sources and benthic invertebrates consumers was investigated in a large intertidal area (Western English-Channel, France). The study area is influenced by megatidal conditions and characterised by salt marshes in the sheltered part, and seasonal Ulva spp. blooms. The spatio-temporal variability in the structure of the benthic food web was analysed at the scales of both the whole bay and the different assemblages, which constitute the mosaic of habitats. Inferences on potential sources fuelling the food web were supported by spatio-temporal patterns based on covariations and stable isotope trajectory analysis. Results highlighted that phytoplankton, microphytobenthos and SOM were, most likely, the main food sources. The trophic connectivity between salt marsh and benthic habitats within the bay was limited to some macrofauna species inhabiting muddy creeks within the salt marsh. Unexpectedly, the influence of Ulva spp. blooms appeared also limited. Spatial patterns illustrates the constancy of the spatial variability in the benthic pelagic coupling, with a higher influence of microphytobenthos in the upper shore compared to low shore assemblages. This first attempt to characterize intertidal benthic food web constitutes a relevant baseline for the conservation of the bay of Saint-Brieuc where a national Nature Reserve has been created in 1998 for the conservation of overwintering birds. The spatial and temporal patterns of the benthic food web observed in this study (1) confirm the importance to consider food web variability at spatial and temporal scales from sampling designs to data analysis, and (2) demonstrate the ability of the stable isotope trajectory analysis framework to highlight food web dynamics.

Variability of Plant and Surface Soil Carbon Concentration Among Saltmarsh Habitats in Ireland

Variability of Plant and Surface Soil Carbon Concentration Among Saltmarsh Habitats in Ireland

Quantification of blue carbon in tropical salt marshes and their role in climate change mitigation

Vegetated coastal ecosystems (VCE) display a promising potential to act as natural carbon sinks in climate change mitigation. Although growing interest in wetland carbon has intensified the global level carbon stock estimation studies, large knowledge gaps and uncertainties remain, particularly in tropical salt marshes in the South and Southeast Asian regions. Therefore, the current study aims to quantify the organic carbon stocks in the salt marsh habitats on the Northwest coast of Sri Lanka and to showcase the relevance of salt marsh carbon in local and regional contexts. Vegetation and soil up to a depth of 50 cm were sampled from four sites representing the Wedithalathive Nature Reserve (WNR). Species-specific allometric relationships developed for the major succulent halophytic species indicated a significant positive correlation between dry biomass and plant height. The loss-on-ignition (LOI) technique was applied in combination with a carbon conversion factor to calculate the soil organic carbon (SOC) content across 4 depth intervals. The study provided an average total organic carbon (TOC) storage of 73 ± 14.47 Mg C ha−1 up to a depth of 50 cm, in which the aboveground vegetation accounted for ~2% share. Sri Lankan salt marshes hold 2.01 Tg of organic carbon and directly reflect their potential for inclusion in Nationally Determined Contributions (NDCs) under the Paris Agreement. This has been the first comprehensive study on salt marsh blue carbon stocks in Sri Lanka and the findings of this study will strengthen the knowledge base on regional and global saltmarsh carbon stocks and their potential role in climate change mitigation.

Salt marsh restoration: an overview of techniques and success indicators.

Coastal wetlands including salt marshes are among the most productive ecosystems on Earth. They are known for improving the quality of coastal water and provisioning coastal fisheries. However, this ecosystem is under potential threat due to urban coastal land reclamation, limited sediment supply, increased nutrient/eutrophication, and sea level rise. Therefore, restoration efforts to protect the degraded salt marsh habitat are considerably increasing worldwide. In this paper, we present an overview of salt marsh restoration techniques and success indicators. Published scientific literature in English language was collected by searching the most relevant keywords from popular search engines, namely, Google Scholar, Scopus, and Mendeley to get the information about salt marsh restoration techniques and success indicators. This study comprehensively reviewed data from 78 peer-reviewed papers. Results indicated that much of the salt marsh was restored through assisted abiotic strategies (e.g., recovery of tidal exchange, managed realignment, and sediment level amendment). A total of 214 indicators were found, spanning over six major ecological attributes such as structural diversity, ecosystem functions, physical conditions, species composition, external exchange, and absence of threat. Author keywords analysis revealed several hotspots for recent research (e.g., 16s rRNA, fungi, microbial communities, carbon accumulation, and blue carbon). This paper proposes a model for restoring degraded salt marsh, as well as tracking their success.The information presented here will assist the marine ecosystem restoration practitioners in getting a comprehensive understanding of salt marsh restoration success evaluation.

Proximate Composition, Bioactive Compounds, and Antioxidant Potential of Wild Halophytes Grown in Coastal Salt Marsh Habitats.

Halophytes have been characterized as a potential resource for fiber, food, fodder, and bioactive compounds. Proximate composition, bioactive compounds, and antioxidant activity of five wild dominant halophytes (Arthrocnemum macrostachyum, Halocnemum strobilaceum, Limoniastrum monopetalum, Limoniastrum pruinosum, and Tamarix nilotica) naturally growing along the Nile Delta coast were assessed. The soil supporting these halophytes was sandy to sand-silty, alkaline, with low organic carbon, and relatively high CaCO3. H. strobilaceum attained the highest moisture content, ash, crude fiber, lipids, and total soluble sugars. L. monopetalum showed the highest content of crude protein (18.00%), while T. nilotica had the highest content of total carbohydrates. The studied halophytes can be ranked according to their nutritive value as follows: H. strobilaceum > L. monopetalum > A. macrostachyum > L. pruinosum > T. nilotica. A. macrostachyum attained the highest amount of Na+, K+, Ca2+, and Mg2+. A. macrostachyum showed a high content of phenolic compounds, while H. strobilaceum was rich in tannins and saponin contents. The MeOH extract of A. macrostachyum and H. strobilaceum exhibited substantial antioxidant activity. The present results showed that the studied halophytes could be considered as candidates for forage production or used as green eco-friendly natural resources for bioactive compounds.

Comparison of Two Methods for Detecting Atlantic Salt Marsh Mink

ABSTRACTThe Atlantic salt marsh mink (ASMM; Neovison vison lutensis) has a limited distribution in Florida and may be vulnerable to extirpation through habitat loss or degradation. To evaluate ASMM population status, survey methods are needed that are effective and practical in salt marsh habitat where mink are difficult to detect. In 2013–2014, we compared the effectiveness of 2 survey methods, spotlight surveys and floating camera traps, to estimate site occupancy and detectability of ASMM in northeast Florida. Using spotlight surveys, we sampled 148, 1‐km2 units over 3 months and detected ASMM in 9% of the sampled units. With floating camera traps, we sampled 42, 1‐km2 units over 10 months and detected ASMM in 36% of sampled units. Floating cameras traps were a more effective survey method for ASMM, resulting in higher estimated site occupancy (Ψ = 0.36) and detection probability (P = 0.46) when compared to spotlight surveys (Ψ = 0.15, P = 0.24). Spotlight surveys for ASMM were effective only at peak high tide when water levels rise to the height of the marsh grass and many individuals take cover on floating vegetation. We conducted all spotlight surveys during times of peak high tide, but tide height varied by location across the study area and likely affected detection rates. As a result, we detected ASMM only during spotlight surveys in the northern part of our study area, where mean tide height was 1.97 m compared with 1.46 m in the southern part of the study area. Therefore, we recommend floating camera traps for future surveys of ASMM to estimate site occupancy. © 2021 The Wildlife Society.

E-scape: Consumer-specific landscapes of energetic resources derived from stable isotope analysis and remote sensing.

Energetic resources and habitat distribution are inherently linked. Energetic resource availability is a major driver of the distribution of consumers, but estimating how much specific habitats contribute to the energetic resource needs of a consumer can be problematic.We present a new approach that combines remote sensing information and stable isotope ecology to produce maps of energetic resources (E‐scapes). E‐scapes project species‐specific resource use information onto the landscape to classify areas based on energetic importance.Using our E‐scapes, we investigated the relationship between energetic resource distribution and white shrimp distribution and how the scale used to generate the E‐scape mediated this relationship. E‐scapes successfully predicted the size, abundance, biomass, and total energy of a consumer in salt marsh habitats in coastal Louisiana, USA at scales relevant to the movement of the consumer.Our E‐scape maps can be used alone or in combination with existing models to improve habitat management and restoration practices and have potential to be used to test fundamental movement theory.

Omics-based ecosurveillance uncovers the influence of estuarine macrophytes on sediment microbial function and metabolic redundancy in a tropical ecosystem

Vertical zonation within estuarine ecosystems can strongly influence microbial diversity and function by regulating competition, predation, and environmental stability. The degree to which microbial communities exhibit horizontal patterns through an estuary has received comparatively less attention. Here, we take a multi-omics ecosurveillance approach to study environmental gradients created by the transition between dominant vegetation types along a near pristine tropical river system (Wenlock River, Far North Queensland, Australia). The study sites included intertidal mudflats fringed by saltmarsh, mangrove or mixed soft substrata habitats. Collected sediments were analyzed for eukaryotes and prokaryotes using small sub-unit (SSU) rRNA gene amplicons to profile the relative taxonomic composition. Central carbon metabolism metabolites and other associated organic polar metabolites were analyzed using established metabolomics-based approaches, coupled with total heavy metals analysis. Eukaryotic taxonomic information was found to be more informative of habitat type. Bacterial taxonomy and community composition also showed habitat-specificity, with phyla Proteobacteria and Cyanobacteria strongly linked to mangroves and saltmarshes, respectively. In contrast, metabolite profiling was critical for understanding the biochemical pathways and expressed functional outputs in these systems that were tied to predicted microbial gene function (16S rRNA). A high degree of metabolic redundancy was observed in the bacterial communities, with the metabolomics data suggesting varying degrees of metabolic criticality based on habitat type. The predicted functions of the bacterial taxa combined with annotated metabolites accounted for the conservative perspective of microbial community redundancy against the putative metabolic pathway impacts in the metabolomics data. Coupling these data demonstrates that habitat-mediated estuarine gradients drive patterns of community diversity and metabolic function and highlights the real redundancy potential of habitat microbiomes. This information is useful as a point of comparison for these sensitive ecosystems and provides a framework for identifying potentially vulnerable or at-risk systems before they are significantly degraded.

Salt Marsh and Tidal Flat Area Distributions Along Three Estuaries

Estuarine landscapes form through interactions between fluvio-coastal processes and ecological processes within the boundaries imposed by hard substrate layers and man-made dikes and dams. As estuaries are ecologically valuable areas, monitoring and quantification of trends in habitats is needed for objective comparison and management. However, datasets of tidal flat and saltmarsh habitats along entire estuaries are scarce. The objective was to compare trends of biogeomorphological areas and habitat transitions along three estuaries in the Netherlands and assess whether these are generally comparable or mainly determined by system-specific histories. We present data for these estuaries obtained by automated classification of false-color aerial imagery. The automated method allows objective mapping of entire estuaries at unprecedented resolution. The estuaries are dominated by subtidal areas and tidal flats. The tidal flats have similar area along the estuaries while saltmarsh area decreases. Collective lengths of ecologically important transitions between saltmarsh, low-energy tidal flats and water differ more between the estuaries. These variations are due to presence of mid-channel bars and shore-connected embayments. Saltmarsh area is mainly determined by the different formation and embankment histories of the estuaries, embayments and side-branches. Much of the past saltmarsh flanking the estuaries was lost due to past land reclamation. In one system, ecologically important low-energy tidal flats are reduced by a sudden decrease of tidal amplitude, causing increase of subtidal area at the cost of intertidal area. Large areas of high-energy tidal flats in one estuary remain unexplained. The automated method can be applied in other estuaries, provided that high-quality areal imagery is available. Extensions of the data to other estuaries would allow for system-scale trend comparison between estuaries of ecologically relevant biogeomorphological characteristics.

Two different new Tamarix smyrnensis Bunge associations on the Yeşilırmak Delta Plain (Samsun/Türkiye)

The aim of this paper is to deal with syntaxonomical and ecological characteristics of Tamarix smyrnensis communities developed on both salt marsh and riparian habitats of the Yeşilırmak Delta Plains. The floristic composition of the communities was analysed by Braun-Blanquet method and the effect of edaphic parameters on the communities were determined using ordination techniques (CCA). The habitat types were identified according to the European Nature Information System (EUNIS) habitat coding list. Junco acuti-Tamaricetum smyrnensis ass. nov. developed on salt marshes and belonging to the alliance of Tamaricion tetragynae, and Tamaricetum tetrandrae-smyrnensis ass. nov. developed on meander banks/river island (eyot) and belonging to the alliance of Rubo sancti—Nerion oleandri distributed under influence of electrical conductivity (EC) of soil. Additionally, it was observed that both associations belonged to subunits of Mediterraneo-Macaronesian tamarisk thickets according to EUNIS.

Eco-hydrology as a driver for tidal restoration: Observations from a Ramsar wetland in eastern Australia.

Land reclamation projects and the installation of drainage infrastructure has impacted coastal wetlands worldwide. By altering water levels and inundation extent, these activities have changed the viable ecosystems onsite and resulted in the proliferation of freshwater species. As more than 50% of tidal wetlands have been degraded globally over the last 100 years, the importance of this issue is increasingly being recognised and tidal wetland restoration projects are underway worldwide. However, there are currently limited sites where large-scale reintroduction of tidal flushing has been implemented with the explicit aim to foster the growth of a threatened ecosystem. In this study, the tidal restoration of an internationally recognised Ramsar listed wetland in eastern Australia is described to highlight how coastal saltmarsh can be targeted by mimicking inundation depths and hydroperiod across the 410-ha site. Coastal saltmarsh is particularly important to this site as it is part of the east Australasian flyway for migratory birds and the minimum saltmarsh extent, as listed within the Ramsar’s limits of acceptable change, have been breached. To recreate coastal saltmarsh habitat onsite, water level and hydroperiod criteria were established based on similar vegetation patterns within the adjacent estuary. A calibrated 2D hydrodynamic model of the site was then used to test how the preferred inundation criteria could be applied to the largest possible restored wetland area. Once optimised, a synthetic tidal signal was implemented onsite via automated hydraulic controls. The onsite vegetation response over an 8-year period was assessed to highlight the ecosystem response to controlled tidal inundation and denoted substantial saltmarsh expansion during the period. The techniques applied onsite have successfully met the restoration targets and can be applied at similar sites worldwide, offsetting sea level rise impacts to natural inundation hydroperiod.

Saltmarsh vegetation and social environment influence flexible seasonal vigilance strategies for two sympatric migratory curlew species in adjacent coastal habitats

BackgroundAnimals need to adjust their vigilance strategies when foraging between physically contrasting vegetated and non-vegetated habitats. Vegetated habitats may pose a greater risk for some if vegetation characteristics function as a visual obstruction but benefit others if they serve as protective shelter. Variation in group size, presence of similar species, along with variation in environmental conditions and anthropogenic disturbance can also influence vigilance investment.MethodsIn this study, we quantified the vigilance behaviour of two large-bodied, sympatric migratory curlew species—Far Eastern Curlew (Numenius madagascariensis) and Eurasian Curlew (N. arquata)—in vegetated Suaeda salsa saltmarsh and non-vegetated mudflat habitat in Liaohekou National Nature Reserve, China. We used linear mixed models to examine the effects of habitat type, season, tide time, flock size (conspecific and heterospecific), and human disturbance on curlew vigilance investment.ResultsBoth species spent a higher percentage of time under visual obstruction in S. salsa habitat compared to mudflat habitat but in response, only Far Eastern Curlew increased their percentage of vigilance time, indicating that visual obstruction in this habitat is only a concern for this species. There was no evidence that S. salsa vegetation served as a form of cryptic background colouration since neither species decreased their vigilance effect in S. salsa habitat in spring compared to the autumn migration season. The effect of curlew social environment (i.e. flock size) was habitat dependent since percentage of vigilance time by curlews in saltmarsh increased with both the number of individual curlews and number of other birds present, but not in mudflat habitat.ConclusionsWe conclude that both migratory curlew species exhibit a flexible vigilance adjustment strategy to cope with the different environmental and social conditions of adjacent and sharply contrasting coastal habitats, and that the trade-off between the risks of foraging and the abundance of prey may be a relatively common phenomenon in these and other shorebird populations.

Carbon and Nitrogen Stocks and Burial Rates in Intertidal Vegetated Habitats of a Mesotidal Coastal Lagoon

Coastal vegetated ecosystems such as saltmarshes and seagrasses are important sinks of organic carbon (OC) and total nitrogen (TN), with large global and local variability, driven by the confluence of many physical and ecological factors. Here we show that sedimentary OC and TN stocks of intertidal saltmarsh (Sporobolus maritimus) and seagrass (Zostera noltei) habitats increased between two- and fourfold along a decreasing flow velocity gradient in Ria Formosa lagoon (south Portugal). A similar twofold increase was also observed for OC and TN burial rates of S. maritimus and of almost one order of magnitude for Z. noltei. Stable isotope mixing models identify allochthonous particulate organic matter as the main source to the sedimentary pools in both habitats (39–68%). This is the second estimate of OC stocks and the first of OC burial rates in Z. noltei, a small, fast-growing species that is widely distributed in Europe (41,000 ha) and which area is presently expanding (8600 ha in 2000s). Its wide range of OC stocks (29–99 Mg ha−1) and burial rates (15–122 g m2 y−1) observed in Ria Formosa highlight the importance of investigating the drivers of such variability to develop global blue carbon models. The TN stocks (7–11 Mg ha−1) and burial rates (2–4 g m−2 y−1) of Z. noltei were generally higher than seagrasses elsewhere. The OC and TN stocks (29–101 and 3–11 Mg ha−1, respectively) and burial rates (19–39 and 3–5 g m−2 y−1) in S. maritimus saltmarshes are generally lower than those located in estuaries subjected to larger accumulation of terrestrial organic matter.

Basin infill increases seaward sediment delivery in small, tide-dominated estuaries

Estuaries are sinks for sediment and evolve through a series of infill stages. In the early stages of infill, sediment is stored in the central basin due to ample accommodation space. In the late stages of infill, accommodation space decreases and a higher proportion of the sediment load is routed seaward. To predict changes in the seaward sediment delivery of estuaries, we must first understand how they evolve and how their storage capacity changes over time. In this study, we present an analysis of the current infill stage and relative importance of 15 small, tide-dominated estuaries draining into semi-enclosed Moreton Bay (MB), Australia. Our work shows that these estuaries all exist in a mature (i.e. late) stage of infill regardless of their catchment or antecedent basin size. Due to their high degree of infill and densely urbanised catchments, these estuaries are likely to be contributing a large amount of sediment into MB relative to their size. Using existing infill models from the literature, and Eprapah Creek estuary as a case study, we mapped vegetation and facies unit changes from 1955 to 2019 and collected sediment cores to develop a conceptual infill model for these small estuaries. We show there has been an increase in mangrove and alluvial units and a decrease in open water and saltmarsh habitats. These changes are likely a result of increased sediment bypassing due to the infilling of the estuary. Over 50 m of mangrove progradation at the shoreline has occurred on average since 1955, with progradation rates being highest adjacent to the estuary mouth. Our work illustrates that estuary morphology and infill stage can impact the seaward sediment delivery potential for small tide-dominated estuaries. This is of important for semi-enclosed shorelines globally as sediment is not as easily removed seaward compared to shorelines along the open ocean.

Prioritization of Vulnerable Species Under Scenarios of Anthropogenic-Driven Change in Georgia's Coastal Plain

Abstract Effective management of wildlife populations benefits from an understanding of the long-term vulnerability of species to anthropogenic stressors. Exposure to potential habitat change is one measure of vulnerability that wildlife managers often use to assess and prioritize individual species or groups of species for resource allocation or direct management actions. We used species distribution models for 15 species occurring in the coastal plain ecoregion of Georgia to estimate the current amount and distribution of potential habitat and then predict exposure to changes in habitat due to inundation from sea level rise (using the Sea Level Affecting Marshes model) and urban growth (using the Slope Land-use Excluded Urban Topology Hillshade Growth model) for four future time points. Our results predict that all focal species were likely to experience some exposure to habitat change from either sea level rise or urbanization, but few species will experience high exposure to change from both stressors. Species that use salt marsh or beach habitats had the highest predicted exposure from sea level rise (25–69%), while species that use more inland habitats had the highest predicted exposure to urban growth (10–20%). Our models are a resource for managers considering tradeoffs between prioritization schemes under two future stressors. Results suggest that managers may need to prioritize species (or their habitats) based on the predicted magnitude of habitat loss, while also contextualizing prioritization with respect to the current amount of available protected habitat and species global vulnerability.

How grazing management can maximize erosion resistance of salt marshes

Abstract Combining natural saltmarsh habitats with conventional barriers can provide a sustainable and cost‐effective alternative for fully engineered flood protection, provided that a minimal salt marsh width can be guaranteed for a long period. Hence, it is essential to understand both the key factors and management options driving the lateral erodibility/stability of salt marshes. We aimed to determine how salt marsh management (i.e. grazing by large vs. small grazers vs. artificial mowing), marsh elevation and marsh age affect soil stability (i.e. soil collapse) and intrinsic lateral erodibility of salt marshes (i.e. particle‐by‐particle detachment). Soil cores were collected in high and low marshes (above and below 0.5 m MHWL, respectively) of different ages. At these locations, we compared cores from grazed areas to cores inside grazer exclosures, with and without artificial mowing. All cores were exposed to waves in flumes to test their stability and lateral erodibility. All soil cores were characterized by a stable fine‐grained layer deposited on top of readily erodible sand. The thickness of the fine‐grained layer was a key parameter in reducing salt marsh instability (cliff collapse). This layer thickness increased with marsh age and at lower elevations, but decreased with cattle grazing due to compaction. The erosion resistance of the fine‐grained layer increased with (a) large grazers that compacted the soil by trampling, (b) mowing that excluded soil‐bioturbating species, and (c) grazing by small grazers that promoted vegetation types with higher root density. Synthesis and applications. Overall, marshes with thinner cohesive and/or fine‐grained top layers are more sensitive to lateral erosion than marshes with deep cohesive soils, independently of the management. Grazing and artificial mowing can reduce the erodibility of fine‐grained soils, making salt marshes more resilient to lateral erosion. However, compaction by large grazers simultaneously leads to thinner fine‐grained layers and lower elevation, potentially leading to more inundation under sea‐level rise. Hence, to effectively manage salt marshes to enhance their contribution to coastal protection, we recommend (a) moderate/rotational livestock grazing, avoiding high intensity grazing in sediment‐poor systems sensitive to sea‐level rise and (b) investigating measures to preserve small grazers.

Assessing the Viability of American Horseshoe Crab (Limulus polyphemus) Embryos in Salt Marsh and Sandy Beach Habitats.

AbstractFor animal embryos that develop externally, the physio-chemical environment can substantially affect offspring viability. In the case of the American horseshoe crab (Limulus polyphemus), sediment conditions along estuarine shorelines influence development rates and embryonic viability. Sandy beach habitats are considered to have optimal conditions for horseshoe crab embryonic development; however, spawning is often observed outside of these optimal habitats, in areas such as salt marshes, where reduced oxygen availability is thought to decrease the viability of eggs laid in these sediments. We excavated horseshoe crab eggs, embryos, and trilobites laid naturally in marsh and beach sediments in South Carolina to compare their development and viability between habitats. We found all developmental stages in both marsh and beach habitats. For two of three sampling areas, trilobites were more likely to be found at beaches than at marshes. Multivariate analyses demonstrate that the prevalence of early and middle developmental stages was similar between habitats but that beaches had a greater proportion of late-stage trilobites than marshes. The lower likelihood of finding trilobites at some marshes may reflect differences in spawning phenology between habitats or reduced rates of embryonic development in marshes compared to beaches, leading to potentially different developmental timelines rather than a true reduction in viability. Nevertheless, the substantial proportions of eggs laid in salt marshes that survive to the trilobite stage indicate that spawning in this habitat could represent a previously underappreciated source of recruitment for horseshoe crab populations that may need to be incorporated into population assessments.

Of marsh and mangrove: coupled biophysical and anthropogenic drivers of 20th century wetland conversion in Tampa Bay Estuary, Florida (USA)

Dense mangrove swamps currently dominate tidal wetlands of the Tampa Bay Estuary System on the central peninsular Gulf Coast of Florida (USA). Late-19th century Coast and Geodetic Survey topographical charts and Government Land Office surveys, however, depict wetland systems dominated by salt marsh—therefore suggesting mangrove dominance as a product of 20th century encroachment. To clarify the primary drivers of ecosystem change, this study integrates sedimentological, paleobotanical, and radiometric analyses of sediment cores collected in 2018 with analyses of aerial photography taken between 1940 and 1997. Results empirically ground truth the wetland conversions inferred through analytical comparisons of historical and modern mapping and establish a high-resolution chronology for coastal environmental change. These results showed that salt marsh and salt prairie habitats persisted within Tampa Bay study areas until the mid-20th century. Mangrove forest rapidly encroached the study areas over a 20 year interval, between 1960 and 1980, immediately following intensive ditching for mosquito control. The findings demonstrate how coastal geoengineering, mangrove autoecology, and sea-level rise interacted across the late-20th century to accelerate the creation of novel seascapes.

Coastal Meadow Vegetation Following a Century of Shielding Behind a Dike

It is still common practice in Europe to dike salt marshes for agricultural use. This impacts both the vegetation and physical environment of the marsh. We studied the plant community, environmental conditions, and determined correlations between vegetation cover and diversity with environmental factors on an enclosed marsh, which has been behind a dike since 1890. Vegetation data from both salt marshes without dikes and fresh meadows are routinely sampled by the Danish Environmental Protection Agency and were here used to assess whether the plant community of the shielded marsh resembled that of either salt marshes or fresh meadows. The century-long elimination of tidal and storm flooding has resulted in low salinity levels (0.4–5.13 ppt), low available P (0.36–4.90 mg/100 g soil), and high total N (0.68–28.82 g/kg). The plant community of the shielded marsh demonstrated a mean species richness (11.4) similar to that of other salt marshes but was no longer characterized by the same composition of halophytes (ANOSIM, p < 0.001). However, despite the century-long shielding the vegetation does not resemble that of the nearby fresh meadow community (ANOSIM, p < 0.001). Therefore, prohibiting tidal floodings by dikes does not protect the salt marsh habitat but instead results in a habitat that contains both halophytes and glycophytes.