Tidal Marsh Habitat Research Articles

Revisiting the effectiveness of biodiversity offsets in coastal wetlands of China through landscape connectivity

We modified the landscape connectivity calculation method and applied it to assess changes in temporal connectivity under different offsetting scenarios in the Yellow River Delta High-efficiency Ecological Economic Zone of China. We evaluated landscape connectivity based on resistance surfaces, least-cost distances, habitat areas, and the probability of dispersal between wetland patches in the landscape. The landscape connectivity declined between 1980 and 2015, with the degree of decline varying with the type of wetland. The cumulative percentages of freshwater marsh, salt marsh, and tidal marsh habitat areas that could be offset were 100 %, 100 %, and 34 %, respectively. However, the maximum landscape connectivity that was compensated for was only 1.2–10.4 %. When the offset patches were restored to freshwater marsh, the highest connectivity of coastal wetlands was achieved. There were substantial gaps between the area of habitat restoration offset required to achieve no net loss and the landscape connectivity that would ensure ecological effectiveness. The compensation area required to achieve no net loss of landscape connectivity was greater than that required to achieve no net loss of habitat area. We provide guidance for policy makers on how to implement offsetting to develop and manage green corridors, thus allowing movement that will ensure species’ survival. It was suggested that the passive restoration of isolated coastal wetland may be difficult to achieve. Policies that seek to increase landscape connectivity offsets can effectively promote population diffusion and migration, avoid habitat fragmentation, and are key to improving no net loss effectiveness.

Improved mapping of coastal salt marsh habitat change at Barnegat Bay (NJ, USA) using object-based image analysis of high-resolution aerial imagery

Tidal wetlands are valued for the ecosystem services they provide yet are vulnerable to loss due to anthropogenic disturbances such as land conversion, hydrologic modifications, and the impacts of climate change, especially accelerating rates of sea level rise. To effectively manage tidal wetlands in face of multiple stressors, accurate studies of wetland extent and trends based on high-resolution imagery are needed. We provide salt marsh delineations for Barnegat Bay, New Jersey, by means of object-based image analysis of high-resolution aerial imagery and digital elevation models. We performed trends analyses of salt marsh extent from 1995 to 2015 and estimated drivers of marsh area change. We found that in 1995, 8830 ± 390 ha were covered with marsh vegetation, while in 2015 only 8180 ± 380 ha of salt marsh habitat remained. The resulting net loss rate of 0.37% yr−1 is equivalent to historic loss rates since the 1970s, indicating that despite regionally accelerating relative sea level rise and purported eutrophication, salt marsh loss rates at Barnegat Bay remain steady. The main drivers of salt marsh loss are excavations for mosquito control (409 ha), edge erosion (303 ha) and ponding (240 ha). Upland migration of salt marsh did not completely mitigate these losses but accounted for a gain of 147 ha of tidal marsh habitat. The methodology presented herein yielded accurate salt marsh delineations (>90%) and trend detection (85%), outperforming low-resolution wetland delineations used in coastal management. This study demonstrates the suitability of high-resolution imagery for the detection of open water features. For the purposes of salt marsh change detection and the identification of change drivers, management and conservation agencies should make use of high-resolution imagery whenever feasible.

Mr. Mister: Rockin' the Aedes of the San Francisco Bay Salt Marshes.

Mist sprayers (MS) are being rapidly adopted nationwide for applying larvicides to control peridomestic Aedes aegypti. Because MS can loft large quantities of larvicide over relatively long distances, we examined its efficacy in a tidal marsh habitat for controlling Ae. dorsalis. Liquid Vectobac 12AS larvicide, containing Bacillus thuringiensis israelensis, was applied at 1.16 liter/ha using a MS. Cards that change color when exposed to liquid were placed perpendicular to the path of the MS showed that the larvicide mist traveled up to 60 m from the MS and did not extend to 90 m. Use of the MS enabled a 4-fold increase in total hectares treated during 2020-21 relative to the prior 2 years without an increase in staff time. Notably, there was 83% reduction in the quantity of Ae. dorsalis larvae at 5 days posttreatment. Similarly, there was 63% reduction in adult female Ae. dorsalis that were collected in encephalitis virus surveillance traps from nearby communities relative to the prior 2 years. There were 2.3-fold fewer requests for service to address a mosquito problem from residents of communities that abut the tidal marshes, suggesting the applications had a positive impact on these communities. The MS offer an attractive alternative to hand treatments in tidal marshes where the use of unmanned aircraft or all-terrain vehicles is prohibited by national wildlife refuge managers.

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.

Enhancing marsh elevation using sediment augmentation: A case study from southern California, USA

Tidal marshes are an important component of estuaries that provide habitat for fish and wildlife, protection from flooding, recreation opportunities, and can improve water quality. Critical to maintaining these functions is vertical accretion, a key mechanism by which tidal marshes build elevation relative to local sea level. The beneficial use of dredged material to build marsh elevations in response to accelerating sea level rise has gained attention as a management action to prevent habitat loss over the coming decades. In January 2016, a sediment augmentation project using local dredged material was undertaken at Seal Beach National Wildlife Refuge in Anaheim Bay, California, USA, to benefit tidal marsh habitat and the listed species it supports. The application process added 12,900 cubic meters of sediment with an initial, average 22-cm gain in elevation over a 3.2-hectare site. Due to sediment characteristics and higher than anticipated elevations in some areas, vegetation colonization did not occur at the expected rate; therefore, adaptive management measures were undertaken to improve hydrology of the site and facilitate vegetation colonization. More case studies that test and monitor sea level adaptation actions are needed to assist in the planning and implementation of climate-resilient projects to prevent coastal habitat loss over the coming century.

Seasonality and Characterization Mapping of Restored Tidal Marsh by NDVI Imageries Coupling UAVs and Multispectral Camera

Salt marsh evolution is strongly affected by tidal processes and ecology, which regulate sediment accretion and erosional rates. A balance between marsh erosion and deposition in a restored tidal wetland is crucial for analyzing restoration strategies to adopt in a natural context. Here, we present an integrated approach monitoring salt marsh seasonal changes over several months in a microtidal restored salt marsh of the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (MD, USA). The project is undertaken at a restoration site where sediment dredged from the shipping channels in the upper Chesapeake Bay is being used to restore a tidal marsh habitat in mid-Chesapeake Bay. We flew an Unmanned Aerial Vehicle (UAV) with an RGB and a multispectral camera to obtain a high-resolution map of the planimetric position of vegetation and to monitor the health of the marsh vegetation in diverse seasons. Due to its extension of 400 m by 400 m, a total of four flight plans were necessary to cover the entire marsh flying at a 40 m altitude obtaining a 2 cm Ground Sample Distance (GSD). This technique provides reliable results at a very low cost, enabling an accurate assessment of the marsh platforms to be conducted over time, due to both the very high spatial resolution and the precise georeferencing of the images for the comparisons. Our results show seasonal variability in the two dominant species colonizing the low marsh, Spartina alterniflora, and high marsh, Sporobolus pumilus. While the lower marshes showed a higher variability along seasons, the up-land vegetation showed persistent green foliage during cold seasons. Detecting salt marsh evolution and seasonality coupled with field measurements can help to improve the accuracy of hydrodynamic and sediment transport models. Understanding the drivers of salt marsh evolution is vital for informing restoration practices and designs, in order to improve coastal resilience, and develop and coastal management strategies.

Genomic data reveal the biogeographical and demographic history of Ammospiza sparrows in northeast tidal marshes

AbstractAimShaped by climate change and sea‐level rise, tidal salt marshes represent ephemeral systems that are home to only a few species. The dynamic ecological histories of these habitats, however, render it challenging to reconstruct the complete biogeographical histories of their endemic taxa. To better understand the evolutionary history of tidal marsh endemic sparrows, we employ genomic data to evaluate the timing and direction of tidal marsh colonization events and leverage these data to test a series of models describing the biogeographical history of our study taxa.LocationNorth America.TaxonAmmospiza Sparrows.MethodsWe sampled 54 individuals from the Ammospiza clade from freshwater and saltwater habitats. We sequenced whole genomes and generated a dataset containing 21 million SNPs. Detailed phylogenomic analyses were conducted to identify relationships between tidal marsh and freshwater species. These phylogenies were then used to date divergence times and reconstruct the biogeographical history of the clade as well as identify historic signals of introgression.ResultsPhylogenies based on several million SNPs supported well‐resolved clades that correspond to all previous species designations. Demographic modelling within A. nelsoni provided further resolution into the subspecies topology. Phylogenetic and biogeographical reconstructions support a series of saltwater to freshwater colonization events, with some endemic taxa exhibiting associations with tidal marsh habitat over longer evolutionary time‐scales and some habitat transitions occurring as recently as 5,000 years ago.Main ConclusionsBiogeographical and phylogenomic reconstructions support an original freshwater origin of the Ammospiza sparrows currently inhabiting tidal marshes in North America. We also found strong evidence for a saltwater to freshwater transition in A. n. subvirgatus as opposed to the long hypothesized freshwater origin of this group. We conclude that the increased resolution from genomic data paired with an integrative framework of phylogenomic, demographic and biogeographical reconstructions is important for resolving evolutionary histories in complex and ephemeral environments.

High-Resolution Monitoring of Tidal Systems Using UAV: A Case Study on Poplar Island, MD (USA)

Tidal processes regulating sediment accretion rates and vegetated platform erosion in tidal systems strongly affect salt marsh evolution. A balance between erosion and deposition in a restored salt marsh is crucial for analyzing restoration strategies to be adopted within a natural context. Marsh morphology is also coupled with tidal mudflats and channel networks and this makes micro-tidal systems crucial for a detailed assessment of restoration interventions. Here, we present a methodological approach for monitoring channel morphodynamics and vegetation variations over a time frame of six years in a low tidal energy salt marsh of the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (Maryland, USA). The project is a restoration site where sediment dredged from the shipping channels in the upper Chesapeake Bay is used to restore a tidal marsh habitat in mid-Chesapeake Bay. Aerial surveys with an Unmanned Aerial Vehicle (UAV) have been performed for the high-resolution mapping of a small tidal system. Flight missions were planned to obtain a Ground Sample Distance (GSD) of 2 cm. Structure-from-Motion (SfM) and Multi-View-Stereo (MVS) algorithms have been used to reconstruct the 3D geometry of the site. The mapping of channel morphology and an elevation assessment on the mudflat were performed using orthomosaics, Digital Terrain Models (DTMs) and GNSS survey. The results highlight that the workflow adopted in this pilot work is suitable to assess the geomorphological evolution over time in a micro-tidal system. However, issues were encountered for salt marsh due to the presence of dense vegetation. The UAV-based photogrammetry approach with GNSS RTK ground surveys can hence be replicated in similar sites all over the world to evaluate restoration interventions and to develop new strategies for a better management of existing shorelines.

Quantifying blue carbon and nitrogen stocks in surface soils of temperate coastal wetlands

Coastal wetlands are carbon and nutrient sinks that capture large amounts of atmospheric CO2 and runoff of nutrients. ‘Blue carbon’ refers to carbon stored within resident vegetation (e.g. mangroves, tidal marshes and seagrasses) and soil of coastal wetlands. This study aimed to quantify the impact of vegetation type on soil carbon stocks (organic and inorganic) and nitrogen in the surface soils (0–10 cm) of mangroves and tidal marsh habitats within nine temperate coastal blue carbon wetlands in South Australia. Results showed differences in surface soil organic carbon stocks (18.4 Mg OC ha–1 for mangroves; 17.6 Mg OC ha–1 for tidal marshes), inorganic carbon (31.9 Mg IC ha–1 for mangroves; 35.1 Mg IC ha–1 for tidal marshes), and total nitrogen (1.8 Mg TN ha–1 for both) were not consistently driven by vegetation type. However, mangrove soils at two sites (Clinton and Port Augusta) and tidal marsh soils at one site (Torrens Island) had larger soil organic carbon (SOC) stocks. These results highlighted site-specific differences in blue carbon stocks between the vegetation types and spatial variability within sites. Further, differences in spatial distribution of SOC within sites corresponded with variations in soil bulk density (BD). Results highlighted a link between SOC and BD in blue carbon soils. Understanding the drivers of carbon and nitrogen storage across different blue carbon environments and capturing its spatial variability will help improve predictions of the contribution these ecosystems to climate change mitigation.

Biogeomorphic patterns emerge with pond expansion in deteriorating marshes affected by relative sea level rise

AbstractInterior marsh pond formation has been commonly observed in tidal marshes affected by high rates of relative sea level rise (RSLR). However, it is difficult to conclude whether an accretion deficit (accretion which does not keep pace with RSLR) or natural ice and wrack disturbance has driven pond formation. We propose that marsh deterioration caused by accretion deficit can be differentiated from that caused by other disturbances based upon temporal vegetation changes and the spatial configuration of vegetation zones relative to tidal creeks and the marsh platform. We tested this hypothesis in six newly ponded sites within RSLR‐affected marshes in Deal Island, Chesapeake Bay. At each site, we used field surveys and remote sensing to study spatiotemporal dynamics of marsh vegetation, marsh topography, and tidal creek incision. We found flood tolerant plants displaced flood intolerant species over time in the landward direction, or upslope, of ponds. A reverse species transition was observed seaward of ponds because tidal creek incision alleviated interior marsh inundation. The landscape‐scale biogeographic pattern we have recognized sheds light on how plants adapt to chronically reshaped geomorphological configurations of the marsh platform, which differentiates ponding caused by accretion deficit from ponding caused by natural and artificial disturbances. Furthermore, our results point to vegetation patterns that can be used as early warning signals of interior marsh loss to ponding. As ponding has been a major driver of tidal marsh habitat loss in microtidal marshes around the world, early indicators of decline are sorely needed to direct conservation activities.

Isoetes ×blondeaui hyb. nov. (Isoetaceae), a new hybrid quillwort from eastern Quebec, Canada

The hybrid between diploid Isoetes echinospora and tetraploid I. laurentiana is reported from six sites along the St. Lawrence River near Quebec City. Morphological characteristics and distinguishing features are identified, and the binomial I. ×blondeaui, hyb. nov. is proposed. All occurrences are in biogeographically significant freshwater tidal marsh habitat. The hybrid is expected to occur in small numbers within most large I. laurentiana populations.

Improving Estimates of Coastal Carbon Sequestration

A new two-model approach could reduce uncertainties in calculated rates of “blue carbon” accumulation within soils of seagrass, tidal marsh, and mangrove habitats.

Isoetes laurentiana, sp. nov. (Isoetaceae) endemic to freshwater tidal marshes in eastern Quebec, Canada

Morphological, phytogeographic, ecological, preliminary genetic, and C-value evidence indicates that populations of Isoetes confined to freshwater tidal marsh habitats along the St. Lawrence River in Quebec, Canada, represent an undescribed endemic species, proposed here as Isoetes laurentiana sp. nov. The combination of short velum coverage (ca. 10%) over a plain (unstreaked) sporangium, broad (ca. 1.0 mm) erect leaves, small megaspores (ca. 459 μm) with more densely convoluted-reticulate, almost echinate ornamentation, and its occurrence within an exceptional habitat, readily distinguish I. laurentiana from I. tuckermanii A.Braun with which it was formerly combined. Isoetes laurentiana is one of a series of endemic taxa of the floristically extraordinary St. Lawrence River estuary. Some populations of I. laurentiana are immense; in cultivation it demonstrates the capacity for prolific production of new individuals, which is presumably necessary to sustain such local abundance. Isoetes laurentiana is of national and global phytogeographic significance, but is not considered to represent a species at risk according to standards from the International Union for Conservation of Nature.

Empirical observations and numerical modelling of tides, channel morphology, and vegetative effects on accretion in a restored tidal marsh

AbstractTidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine‐grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high‐resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco‐geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood‐ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In‐situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea‐level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience. © 2019 John Wiley & Sons, Ltd.

Using owl pellets to infer habitat associations and clarify the regional distribution of a cryptic shrew

AbstractAccurate knowledge of the distribution of rare species remains a great challenge in conservation biology because these species are prone to extinction and the number of species becoming rare is increasing. However, the distribution of rare species is usually difficult to delimit because of their low abundances and/or small distribution ranges. These difficulties are even greater when they are sympatric with morphologically similar species that can lead to identification errors. Here, we use barn owl (Tyto alba) pellets to infer, indirectly, potential habitat associations of the lesser white‐toothed shrew (Crocidura suaveolens) in the Gulf of Cádiz, south‐western Iberia and to clarify the distribution of the species in this region. In the Gulf of Cádiz, C. suaveolens is a rare species that lives in sympatry with its congener, the greater white‐toothed shrew (Crocidura russula), a much more abundant and extremely similar species. Through several indirect lines of evidence we inferred a possible association of C. suaveolens with tidal marsh habitat. This was a very surprising finding since C. suaveolens is a habitat generalist throughout its global distribution range. The species presented a highly restricted distribution in the Gulf of Cádiz occurring only in four tidal marshes. The causes of this limited distribution remain poorly understood to date, but our results are consistent with the hypothesis that C. suaveolens was displaced to tidal marshes through competitive exclusion by C. russula, although the geomorphological history of the tidal marshes of the Gulf of Cádiz may also explain its regional distribution and the phylogeographical patterns recently described in the region.

Grazer deterrence and fungal inhibition by the invasive marsh grass Phragmites australis and the native sedge Bolboschoenus robustus in a mesohaline marsh

Tidal marsh habitats provide many important functions to coastal areas and are a valuable economic resource. Polyhaline marshes dominated by Spartina alterniflora can experience top-down control by the snail Littoraria irrorata who primarily impact Spartina through facilitating fungal growth on wounds they create. This grazing pressure may have selected for the production of chemical defenses in Spartina and other polyhaline marsh plants that deter snail feeding and fungal growth. Both Spartina and Littoraria can co-occur in mesohaline marshes that line the Chesapeake Bay, but little is known about interactions between this snail and plants in this habitat. Plant diversity, identity, and consumer abundance can differ between poly- and mesohaline marshes, and this may yield different patterns in the two marsh types. We investigated whether two abundant plants in a Chesapeake Bay mesohaline marsh of salinity ~ 13ppt deterred snail feeding and inhibited fungal growth. Through a bioassay-guided fractionation approach, we assessed palatability to snails and growth of the fungus Phaeosphaeria spartinae in response to chemical components in the invasive marsh grass Phragmites australis and the native sedge Bolboschoenus robustus. Both plants possessed chemicals that significantly deterred snail feeding compared to Spartina chemicals. In addition, both plants inhibited fungal growth, mediated by multiple metabolites. Snail density in this marsh was low (25 snails m−2), but may be enough to select for defenses in Bolboschoenus, or deterrent and inhibitory metabolites may be selected for by other consumers or factors. Chemical defenses in invasive Phragmites may contribute to its success in the Chesapeake Bay.

Short-Term Resilience of New Jersey Tidal Marshes to Hurricane Sandy

Hurricane Sandy made landfall in the USA on October 29, 2012 and had devastating impacts on human-dominated landscapes in the mid-Atlantic and New England states, but its effects on tidal marsh habitats remain largely undescribed. We evaluated the short-term resilience (a resistance to change or a rapid return to pre-storm conditions) of tidal marshes on Edwin B. Forsythe National Wildlife Refuge, New Jersey by comparing vegetation cover/composition, meadow vole (Microtus pennsylvanicus) relative abundance, and predation rates on artificial bird nests, from three to six months pre-hurricane with seven to 11 months post-hurricane. These three metrics show a high degree of resilience to Hurricane Sandy. Vegetation cover/composition remained similar pre- and post-hurricane, except for five site-specific changes. Although meadow voles were significantly less abundant following the hurricane, we detected a rapid increase from June to July 2013, indicating resiliency via rapid recovery in the population. We also did not observe widespread changes in nest predation rates on artificial nests. Our findings indicate that management actions intended to recover vegetation, small mammals, and nest predators following a large hurricane disturbance may be of less importance than long-term strategies to avoid gradual changes that can reduce ecosystem resilience.

Restoration of Cordgrass Salt Marshes: Limited Effects of Organic Matter Additions on Nitrogen Fixation

The extensive loss of tidal marsh habitat surrounding the San Francisco Bay has led to numerous restoration projects to restore ecosystem function. Native cordgrass (Spartina foliosa) is important for sediment accumulation and nesting habitat for endangered California Ridgway’s Rail (Rallus obsoletus obsoletus), and because salt marshes are typically nitrogen-limited ecosystems, previous restoration studies in California have used nitrogen fertilizers to increase plant growth. This study compared the use of two low-nitrogen, high-carbon fertilizers (Macrosystis pyrifera (kelp) and sodium alginate) to stimulate N2-fixing bacteria inhabiting the S. foliosa rhizosphere in a historic and recently restored marsh in San Francisco Bay. Alginate increased N2-fixation, though there was no observed S. foliosa growth response. Kelp suppressed N2-fixation, and increased the foliar nitrogen content of Salicornia pacifica in mixed Spartina-Salicornia stands. The restored marsh had less than 0.5 μM phosphate in porewaters, suggesting phosphorus, not nitrogen, limits S. foliosa growth in this marsh. Alginate increased rates of N2-fixation and may promote plant growth in marshes exhibiting nitrogen limitation. Phosphate limitation was a surprise considering numerous previous studies indicate nitrogen as the primary limiting nutrient of tidal marsh plants. We recommend first assessing nutrient stoichiometry when considering manipulations to promote plant growth in restored marshes.

Lessons from the past: isotopes of an endangered rail as indicators of underlying change to tidal marsh habitats

ABSTRACTIntroduction: Tidal marsh systems along the Pacific coast of the United States have experienced substantial stress and loss of area and ecosystem function, which we examined by using the endangered California Ridgway’s Rail, Rallus obsoletus obsoletus (‘rail’) as an indicator of its tidal marsh habitat in the San Francisco Estuary. We organized a collection of historical (1885-1940) and modern (2005-2014) rail feathers and analyzed the feather isotope means for delta carbon (δ13C), sulfur (δ34S), and nitrogen (δ15N) by region and time period.Outcomes: Feather isotopes represented the primary foraging habitat during historical then modern time periods. Neither individual nor regional rail feather isotopes suggested freshwater or terrestrial foraging by the rail. Three regions with both historic and modern feather isotopes revealed non-uniform spatial shifts in isotope levels consistent with a marine based food web and significant δ15N enrichment.Discussion: Our results supported the rail’s status as a generalist forager and obligate tidal marsh species throughout the historic record. The variable isoscape trends generated from feather isotope means illustrated a modern loss of the isotopic homogeneity between regions of historical tidal marsh, which correlated with spatially-explicit habitat alterations such as increasing biological invasions and sewage effluent over time.Conclusion: These findings have reinforced the importance of tidal marsh conservation in the face of ongoing underlying changes to these important ecosystems.

Poor transferability of a distribution model for a widespread coastal marsh bird in the southeastern United States

AbstractSpecies distribution models have been applied across a wide range of spatial scales to generate information for conservation planning. Understanding how well models transfer through space and time is important to promote effective species–habitat conservation. Here, we assess model transferability in coastal tidal marshes of the southeastern United States using count data of a widespread marsh bird: the Clapper Rail (Rallus crepitans). We developed species–habitat models at a state level in both South Carolina and Georgia, and then assessed how well top models from each state predicted abundance in the other state. Internally (locally) validated models performed well with reasonable fit (SC: R2 = 0.35, GA: R2 = 0.14), and high significance (P = 0.0005); however, both models performed poorly when predicting abundance from the other state (R2 = 0.03 and 0.003). To assess the consequences of this lack of transferability, we applied the South Carolina‐ and Georgia‐derived parameter estimates to habitat features in South Carolina and identified the top 25% of tidal marsh habitat that each model predicted within the state. There was minimal overlap between model habitat quality predictions (<5%). Our results address the predictive power and uncertainties that arise from using habitat associations and climate models to predict species distributions or abundance in locations without training data. We discuss potential reasons model transferability was not successful and address the need for better regional datasets and the importance of intraspecific variability in response to environmental gradients.