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Whitehead, S.J.; Yeager, K.M.; Feagin, R.A.; Huff, T.P.; Paine, J.G.; Schindler, K.S., and Dixon, T.S., 2024. Growth fault–induced effects on tidal marsh surficial processes and landscape conversion in the Slop Bowl, Brazoria National Wildlife Refuge, Texas. Journal of Coastal Research, 40(1), 64–79. Charlotte (North Carolina), ISSN 0749-0208. The Slop Bowl marsh, located in the Brazoria National Wildlife Refuge on the Texas coast, is an anthropogenically influenced tidal marsh setting that has experienced rapid rates of landscape conversion and loss over the last ∼70 years. This tidal marsh has been affected by recently active faults and several hydrologic barriers (roads, pipeline channels, and active hydrocarbon-extraction well pads). Geophysical field methods and sedimentological analyses were conducted to better understand the effects of these developments on marsh surficial processes. Lithostratigraphy, shallow geophysical data, GPS surveys, radionuclide dating, and organic matter analyses all exhibited influences connected to growth-fault motion. The location and activity of a major growth fault were identified as contributing to subsidence on the downthrown fault block and causing vertical displacement of the marsh surface. Fault motion, in conjunction with the construction of roads, has disrupted the natural hydrologic pathways that once existed. Their combined effects resulted in transition of the land cover over the past several decades from a saline coastal prairie to a tidal marsh–dominant landscape, with continued future submergence anticipated. As the natural laboratory of the Slop Bowl demonstrates, anthropogenic development, neotectonics, and hydrocarbon extraction can have outsized effects on sedimentation processes, with implications for the long-term sustainability of coastal wetland environments in the northern Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Movement and space use information of exploited and imperiled coastal species is critical to management and conservation actions. While satellite telemetry has been successfully used to document movements of marine turtles, the large tag sizes available have limited use on smaller turtle species. We used small Argos-based satellite tags to document movement patterns of diamondback terrapins (Malaclemys terrapin), the only estuarine turtle species in North America. Movement data from ten terrapins in St. Joseph Bay, Florida were gathered between July 13, 2018 and July 22, 2021. We estimated seasonal space use using the daily locations generated from a Bayesian hierarchical state-space model to calculate minimum convex polygons (95% MCP) and kernel density estimates (50% and 95% KDE). Mean tracking duration was 125 days and mean home range size was 9.4 km2 (95% MCP) and 8.1 km2 (95% KDE). Seagrass habitat comprised 55.8% of all home ranges on average, whereas salt marsh comprised a mean of 3.0%. Mean elevation used by terrapins was − 0.13 m (95% MCP) and -0.35 m (95% KDE). Satellite telemetry provided broad-scale spatiotemporal movement and space use data; however, Argos error produced considerable noise relative to true terrapin movements given their size, speed, and behavior. Terrapin home ranges were greater than previously reported and three of the ten terrapins exhibited repeated long-distance, directed movements within the bay. Small patches of salt marsh habitat were centralized within home ranges, despite comprising only a small percentage for each terrapin. Moreover, the percentage of salt marsh present in each core use area was positively correlated with terrapin mass. Although considered an estuarine species, seagrass habitat comprised a large portion of terrapin home ranges; however, our data did not provide the detail necessary to understand how terrapins were using this habitat. As northward-expanding mangroves continue to infringe upon salt marsh habitat, there is potential for negative impacts to terrapin populations across the northern Gulf of Mexico. As salt marsh habitat continues to be infringed upon by northward-expanding mangroves impacts to terrapins across the northern Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Tropicalization is a phenomenon that is changing the structure of ecosystems around the world. Mangrove encroachment is a particular form of tropicalization that may have cascading consequences for resident fauna in subtropical coastal wetlands. There is a knowledge gap regarding the extent of interactions between basal consumers and mangroves along mangrove range edges and the consequences of these novel interactions for consumers. This study focuses on the key coastal wetland consumers, Littoraria irrorata (marsh periwinkle) and Uca rapax (mudflat fiddler crabs), and their interactions with encroaching Avicennia germinans (black mangrove) in the Gulf of Mexico, USA. In food preference assays, Littoraria avoided consuming Avicennia and selectively ingested leaf tissue from a common marsh grass, Spartina alterniflora (smooth cordgrass), a preference that was also previously documented in Uca. The quality of Avicennia as a food source was determined by measuring the energy storage of consumers that had interacted with either Avicennia or marsh plants in the lab and the field. Littoraria and Uca both stored ~10% less energy when interacting with Avicennia, despite their different feeding behaviors and physiologies. The negative consequences of mangrove encroachment for these species at the individual level suggest that there may be negative population‐level effects as encroachment continues. Many studies have documented shifts in floral and faunal communities following mangrove replacement of salt marsh vegetation, but this study is the first to identify physiological responses that may be contributing to these shifts. [ABSTRACT FROM AUTHOR]

Positive species interactions, including facilitation and mutualism, are important in shaping ecological communities through the amelioration of stressful conditions. Facilitation results from traits (e.g., plant growth form) that create benefits for one or more interacting partners. The outcomes of facilitation depend on positive or negative feedbacks between partners, which can determine the stability of interactions over time. We can expand our understanding of these dynamics through a bidirectional approach that identifies the specific mechanisms creating benefits for the associated species, the traits related to those benefits, and the potential for feedbacks to affect amelioration by modifying traits. We characterized an association between the salt marsh plant Limonium carolinianum and mussel Geukensia sp. in the northern Gulf of Mexico. We used a field survey and three field experiments to establish the bidirectional effects of the association, the underlying mechanisms, and the relevant traits for each partner species. Mussels benefitted from Limonium canopies, which ameliorated high temperatures and predation for mussels, increasing survival and recruitment. These positive effects were particularly evident under larger canopies. Mussels enriched sediment organic matter and thus over time are expected to alleviate nutrient limitation for Limonium. Changes in functional traits of both species contributed to facilitation. Limonium both benefitted from and promoted higher mussel density, and mussels both allowed Limonium to grow or retain more leaves and benefitted from stress amelioration under larger canopies. The benefits of the association appear asymmetrical: mussels consistently benefitted in both experiments, but we found only modest positive effects on Limonium, and only over the longer term. These differences likely reflect variation in the seasonality and/or timescale of the facilitative mechanisms. The bidirectional and mechanistic design of our study revealed positive feedbacks that reinforced the traits conferring benefits to each partner, potentially stabilizing this positive interaction. Understanding how feedbacks influence the outcomes of facilitation is increasingly important as anthropogenic stressors increase globally. [ABSTRACT FROM AUTHOR]

Coastal wetlands are one of the most valuable ecosystems; however, they have an uncertain future when faced with increasing sea-level rise (SLR) and both human-induced and environmental stressors. To better understand future marsh resiliency, we examined above- and belowground biomass, carbon (C), nitrogen (N), and phosphorus (P) tissue content and sediment characteristics along a coastal elevation gradient at the Grand Bay National Estuarine Research Reserve (GNDNERR). Vegetation and sediment characteristics were compared across several marsh types, and data was used to make updated predictions using the marsh equilibrium model (MEM). Standing and total biomass increased from 869 g/m2 and 4250 g/m2 respectively at low marsh sites to 2197 g/m2 and 6789 g/m2 at high marsh sites. N/P ratios increased from 10.25 to 20.43 from the low to high marsh, largely driven by decreasing P content in tissues. Spartina alterniflora and Juncus roemerianus biomass and tissue nutrient content were lower than other marshes in the northern Gulf of Mexico. Juncus roemerianus total biomass was around 50% of other coastal Mississippi locations. A meteorologically driven tidal regime and no major freshwater inflow could cause a lack of nutrient and sediment delivery to the marsh surface stunting total biomass and reducing accretion. Under various SLR rate scenarios, the MEM estimates that coastal wetlands at GNDNERR will undergo substantial changes within the next 50–100 years. The lack of nutrient and sediment delivery means that preserving coastal wetlands at GNDNERR will depend on aiding landward marsh migration. [ABSTRACT FROM AUTHOR]

Background: Salt marshes are dominated by the smooth cordgrass Spartina alterniflora on the US Atlantic and Gulf of Mexico coastlines. Although soil microorganisms are well known to mediate important biogeochemical cycles in salt marshes, little is known about the role of root microbiomes in supporting the health and productivity of marsh plant hosts. Leveraging in situ gradients in aboveground plant biomass as a natural laboratory, we investigated the relationships between S. alterniflora primary productivity, sediment redox potential, and the physiological ecology of bulk sediment, rhizosphere, and root microbial communities at two Georgia barrier islands over two growing seasons. Results: A marked decrease in prokaryotic alpha diversity with high abundance and increased phylogenetic dispersion was found in the S. alterniflora root microbiome. Significantly higher rates of enzymatic organic matter decomposition, as well as the relative abundances of putative sulfur (S)-oxidizing, sulfate-reducing, and nitrifying prokaryotes correlated with plant productivity. Moreover, these functional guilds were overrepresented in the S. alterniflora rhizosphere and root core microbiomes. Core microbiome bacteria from the Candidatus Thiodiazotropha genus, with the metabolic potential to couple S oxidation with C and N fixation, were shown to be highly abundant in the root and rhizosphere of S. alterniflora. Conclusions: The S. alterniflora root microbiome is dominated by highly active and competitive species taking advantage of available carbon substrates in the oxidized root zone. Two microbially mediated mechanisms are proposed to stimulate S. alterniflora primary productivity: (i) enhanced microbial activity replenishes nutrients and terminal electron acceptors in higher biomass stands, and (ii) coupling of chemolithotrophic S oxidation with carbon (C) and nitrogen (N) fixation by root- and rhizosphere-associated prokaryotes detoxifies sulfide in the root zone while potentially transferring fixed C and N to the host plant. 5gNBGD5xoDXmzcUFa4HG9g Video Abstract [ABSTRACT FROM AUTHOR]

Marine oil spills continue to be a global issue, heightened by spill events such as the 2010 Deepwater Horizon spill in the Gulf of Mexico, the largest marine oil spill in US waters and among the largest worldwide, affecting over 1,000 km of sensitive wetland shorelines, primarily salt marshes supporting numerous ecosystem functions. To synthesize the effects of the oil spill on foundational vegetation species in the salt marsh ecosystem, Spartina alterniflora and Juncus roemerianus, we performed a meta‐analysis using data from 10 studies and 255 sampling sites over seven years post‐spill. We examined the hypotheses that the oil spill reduced plant cover, stem density, vegetation height, aboveground biomass, and belowground biomass, and tracked the degree of effects temporally to estimate recovery time frames. All plant metrics indicated impacts from oiling, with 20–100% maximum reductions depending on oiling level and marsh zone. Peak reductions of ~70–90% in total plant cover, total aboveground biomass, and belowground biomass were observed for heavily oiled sites at the marsh edge. Both Spartina and Juncus were impacted, with Juncus affected to a greater degree. Most plant metrics had recovery time frames of three years or longer, including multiple metrics with incomplete recovery over the duration of our data, at least seven years post‐spill. Belowground biomass was particularly concerning, because it declined over time in contrast with recovery trends in most aboveground metrics, serving as a strong indicator of ongoing impact, limited recovery, and impaired resilience. We conclude that the Deepwater Horizon spill had multiyear impacts on salt marsh vegetation, with full recovery likely to exceed 10 years, particularly in heavily oiled marshes, where erosion may preclude full recovery. Vegetation impacts and delayed recovery is likely to have exerted substantial influences on ecosystem processes and associated species, especially along heavily oiled shorelines. Our synthesis affords a greater understanding of ecosystem impacts and recovery following the Deepwater Horizon oil spill, and informs environmental impact analysis, contingency planning, emergency response, damage assessment, and restoration efforts related to oil spills. [ABSTRACT FROM AUTHOR]

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Oil spills threaten the structure and function of ecological communities. The Deepwater Horizon spill was predicted to have catastrophic consequences for nearshore fishes, but field studies indicate resilience in populations and communities. Previous research indicates many marsh fishes exhibit avoidance of oil contaminated areas, representing one potential mechanism for this resilience. Here, we test whether prior oil exposure of Gulf killifish Fundulus grandis alters this avoidance response. Using choice tests between unoiled and oiled sediments at one of three randomized concentrations (low: 0.1 L oil m-2, medium: 0.5 L oil m-2, or high: 3.0 L oil m-2), we found that, even at low prior exposure levels, killifish lose recognition of oiled sediments compared to control, unexposed fish. Preference for unoiled sediments was absent across all oil concentrations after oil exposure, and some evidence for preference of oiled sediments at high exposure was demonstrated. These results highlight the lack of response to toxic environments in exposed individuals, indicating altered behavior despite organism survival. Future research should document additional sublethal consequences that affect ecosystem and food web functioning. [ABSTRACT FROM AUTHOR]

Extensive salt marsh restoration is expected in the northern Gulf of Mexico over the next several decades, funded in part by settlements from the 2010 Deepwater Horizon oil spill. Understanding the ecological benefits of restored marshes over time is integral to setting appropriate restoration targets and performance criteria and in determining the restoration area needed to achieve desired restoration goals and offset quantified natural resource injuries. We present a method for quantifying anticipated ecological benefits associated with marsh restoration projects, particularly marsh creation or enhancement through the placement of dredged material, in the northern Gulf of Mexico. Using salt marsh vegetation (percent cover, aboveground biomass, and belowground biomass) and indicator faunal species (periwinkle snails and amphipods) as representative marsh community components, we used resource equivalency analysis (REA) to model projected ecological benefits over time and quantified total net project benefits for a hypothetical marsh creation project in Barataria Bay, Louisiana. Sensitivity analysis of the resulting model suggests that the recovery trajectories for each marsh component were the most important drivers of modeled restoration benefits and that model uncertainty was greatest for marsh fauna, which has limited data availability compared to marsh vegetation and high natural variability. Longer-term monitoring at restored restoration sites and/or targeted monitoring of older restoration projects would reduce variability in the recovery trajectories for the marsh community components examined in this case study and improve the reliability of the REA model for projecting benefits associated with salt marsh restoration. [ABSTRACT FROM AUTHOR]

Aim: Climate change is expected to result in the tropicalization of coastal wetlands in the northern Gulf of Mexico, as warming winters allow tropical mangrove forests to expand their distribution poleward at the expense of temperate salt marshes. Data limitations near mangrove range limits have hindered understanding of the effects of winter temperature extremes on mangrove distribution and structure. Here, we investigated the influence of extreme freeze events on the abundance, height and coverage of black mangroves (Avicennia germinans) near their northern range limit in Louisiana. Location: Coastal Louisiana, USA. Methods: We quantified the relationships between the frequency of extreme freeze events and A. germinans abundance, height and coverage using: (a) mangrove observation points recorded via aerial surveys from a fixed‐wing aircraft; (b) 30 years of temperature data; and (c) mangrove mortality and leaf damage temperature thresholds. We used freeze frequency data and mangrove–climate relationships to evaluate and spatially depict the risk of A. germinans freeze damage across Louisiana. Results: We identified strong negative relationships between the frequency of extreme freeze events and A. germinans abundance, height and coverage. Avicennia germinans is most abundant, tall and continuous along the south‐eastern outer coast of Louisiana, where the frequency of extreme freeze events is reduced (i.e., lower risk of mangrove freeze damage) by the buffering effects of comparatively warm Gulf of Mexico waters. Conversely, the risk of A. germinans freeze damage has historically been very high across Louisiana's Chenier Plain and within more inland wetlands in the Deltaic Plain. Main conclusions: Our analyses advance understanding of how the frequency of extreme freeze events controls the distribution, height and coverage of A. germinans near its northern range limit. In addition to informing climate‐smart coastal restoration efforts, our findings can be used to better anticipate and prepare for the tropicalization of temperate wetlands due to climate change. [ABSTRACT FROM AUTHOR]

Louisiana's coastal marshes are becoming increasingly fragmented due to sea level rise, subsidence, reduced sediment inflow from the Mississippi River, and saltwater intrusion. Many commercially and recreationally fished species rely on the marsh system as nursery habitat, and the resilience of species to further marsh loss and marsh fragmentation is uncertain. We examined the impacts of marsh fragmentation on the blue crab, Callinectes sapidus, a species supporting one of the largest fisheries in coastal Louisiana and which uses marsh edge as nursery habitat. Juvenile and adult abundances were quantified in multiple habitats (bare sediment, marsh edge, and submerged aquatic vegetation [SAV]) within an actively fragmenting coastal marsh. Adult blue crabs were sampled using crab pots, while juveniles were sampled using a throw trap. In general, blue crab density was unrelated to marsh fragmentation, but was instead related to local-scale patterns of habitat availability, including presence and type of vegetation. In tethering experiments to examine predation rates on juvenile blue crabs across habitats, predation rates were lowest in SAV compared with marsh edge or bare sediment. While direct effects of marsh fragmentation on local-scale patterns of blue crab abundance were not observed, marsh fragmentation will likely have indirect effects on blue crab populations through changes in habitat availability. Unless SAV expands into newly created open water areas, providing an alternative nursery habitat for blue crabs, continued marsh fragmentation and loss are expected to have negative impacts on blue crab populations and fisheries through a decrease in available nursery habitat. [ABSTRACT FROM AUTHOR]

Salt marshes are important sites of nitrogen cycling and removal that straddle the land/ocean interface, allowing them to intercept human-derived nitrogen before it reaches coastal waters where it causes problems like hypoxia and harmful algal blooms. In 2010, the Deepwater Horizon oil spill released an estimated five million barrels of crude oil into the Gulf of Mexico, significantly contaminating coastal wetlands over approximately 800 km of shoreline. We investigated microbial nitrogen cycling processes in soil from four salt marshes in Terrebonne Bay, Louisiana, USA that were either exposed or not exposed to Deepwater Horizon oil over the course of 1 year (2013–2014), 2.5–3.5 years post-spill. Specifically, we measured nitrification and denitrification potentials, nitrogen cycling functional gene abundances (nirS, bacterial and archaeal amoA), and soil physical and chemical properties. We show that variation in nitrification and denitrification potentials was independent of site oil exposure. Large year-to-year differences in springtime nitrification potentials were inversely related to plant live belowground biomass, indicating that competition for nitrogen is likely an important control on nitrification. There were positive correlations between nitrification potentials and both soil extractable nitrate concentrations and denitrification potentials, supporting the idea that denitrification is coupled with nitrification. We found no evidence that there was a long-term impact of oil exposure on salt marsh soil microbial nitrogen cycling processes and the nitrogen removal ecosystem service they provide. It is important to note, however, that these impacts could have been masked by high background variability in process rates or loss of oil exposed soil to coastal erosion. [ABSTRACT FROM AUTHOR]

Ragan, A.N. and Wozniak, J.R., 2019. Linking hydrologic connectivity in salt marsh ponds to fish assemblages across a heterogenous coastal habitat. Journal of Coastal Research, 35(3), 545–558. Coconut Creek (Florida), ISSN 0749-0208. In estuarine systems, inundation regime plays a vital role in shaping the physical and chemical characteristics of salt marsh ponds. Along the Texas Gulf Coast, salt marsh ponds are scattered across the coastal marsh landscape, with each pond possessing a varying degree of hydrological connectivity to adjacent estuarine waters. The timing, frequency, and magnitude of connection events can directly influence both the abiotic and biotic components of the ponds. To determine how the degree of hydrological connectivity impacts these systems, discriminant function analysis (DFA) was used to test the ability of environmental variables (e.g., pond size, vegetation, soil type, water column salinity, pH, dissolved oxygen, etc.), fish presence–absence data, and fish relative abundances to predict the level of connectivity of a subset of ponds. In addition, canonical correspondence analysis (CCA) was used to determine whether fish assemblage data (collected via seine and minnow traps) could determine whether pond conditions affect the composition of fish assemblages. Results from the DFA for environmental parameters showed that the model classified ponds correctly to their a priori connectivity classifications; however, no more accurately than random chance. Fish presence–absence data were the least accurate for predicting degree of connectivity, but the relative abundances of those species proved to be an accurate method for pond connectivity classification. Many efforts to understand how an altered hydroperiod impacts marsh complexes along the Texas Gulf Coast have focused on tidal creeks and the vegetated portions of open marshes rather than salt marsh ponds, which can be key habitats for both primary and secondary productivity. This study concentrates on salt marsh ponds to provide a better understanding of how these ecosystems function within the greater marsh landscape. [ABSTRACT FROM AUTHOR]

Anthropogenic pressures, such as diking, construction of dams, and oil spills negatively impact coastal marshes creating growing pressure to preserve and to restore salt marshes due to their critical role in permanently removing nitrate runoff through denitrification as well as other ecosystem services they provide. This study determined denitrification rates across a typical northern Gulf of Mexico salt marsh landscape that included a natural marsh, a tidal creek, and a 21-year-old restored salt marsh. Denitrification capacity, measured with the isotope pairing technique on a membrane inlet mass spectrometer, was comparable across the sites despite significant differences in above and below ground characteristics. Total extractable ammonium concentrations and sediment carbon content were higher at the natural marsh compared to the restored marsh. Hydrogen sulfide concentrations were highest at the creek compared to the vegetated sites and lowest at the restored marsh. This suggests that marsh restoration projects reestablish nitrogen removal capacity at rates similar to those in natural systems and can help to significantly reduce nitrogen loads to the coastal ocean. [ABSTRACT FROM AUTHOR]

Grazing on J. roemerianus (black needlerush), grasshopper abundance, and black needlerush plants was examined in the presence and exclusion of marsh birds. Birds were excluded using a PVC framed exclosure wrapped with bird netting that allowed free passage of marsh grasshoppers. These measurements were taken bi-monthly from April to August 2011 in a black needlerush marsh within the Grand Bay National Estuarine Research Reserve (Moss Point, MS, USA). Grazing metrics, grasshopper abundance, and plant health metrics showed no effect of bird exclusions across all sampling dates. In contrast to other marsh systems with strong trophic cascades (e.g., Spartina alterniflora on US east coast), these results suggest that the primary consumer (grasshoppers) is not affected by the presence of their dominant predator (birds) which leads to no change in the health of the primary producer (black needlerush). Information derived from this study furthers our understanding of the trophic relationships within black needlerush marshes in the northern Gulf of Mexico. [ABSTRACT FROM AUTHOR]

• The differences in leaf traits between ranges indirectly support the EICA hypothesis. • There are parallel latitudinal clines in growth and defense traits between ranges. • Pre-adaptation and phenotypic plasticity lead to parallel latitudinal clines. • The temperature was the main climate factor driving the latitudinal clines of traits. The enemy release and pre-adaptation of alien species often drive their contemporary evolution across latitudinal gradients within its invasive and native ranges. Leaf functional traits constitute an important part of plant functional traits, reflecting their resource acquisition and usage. Thus, comparing the leaf functional traits (growth and defense traits) and latitude patterns of invasive and native plants could provide leading indicators of contemporary evolutionary and adaptative abilities that explain the success of invasive plants. Spartina alterniflora , a coastal wetland invasive plant native to the Atlantic coast and the Gulf of Mexico, has invaded China along the coast wetland (19–40 °N), similar to the United States (27–43 °N). To understand the leaf trait differences and variation across latitudes among continents of S. alterniflora within its invasive and native ranges and determine which factors drive leaf trait variation across latitudes, we investigated the relationship between leaf traits, related to growth (leaf area and specific leaf area), and defensive traits (leaf thickness and leaf toughness) at 10 invaded locations and 15 native locations. We identified correlations between leaf traits and abiotic conditions such as annual mean temperature, tide range, and soil salinity. Compared with native S. alterniflora , Chinese costal S. alterniflora has a larger leaf area and specific leaf area, less leaf thickness, and lower leaf toughness, suggesting that biosynthetic resources are transferred from defense to competitive traits, and indirectly supporting the Evolution of Increased Competitive Ability (EICA) hypothesis. The leaf area, specific leaf area, thickness, and toughness of S. alterniflora from both ranges had similar quadratic latitudinal relationships. Some of these relationships were stronger in the invasive range than the native range, indicating that the leaf traits of invasive S. alterniflora experienced pre-adaptation and had high phenotypic plasticity. Tide range, soil salinity, and especially temperature formed latitudinal gradients in different geographic regions. By analyzing indicators of leaf functional traits across geographical ranges, this study shows that the escape from natural enemies plays an important role in the successful invasion of S. alterniflora , while pre-adaptation and high phenotypic plasticity promote its rapid expansion along the latitudinal gradients. [ABSTRACT FROM AUTHOR]

Over the last several decades, the distribution of the black mangrove Avicennia germinans in the Gulf of Mexico has expanded, in part because it can survive the occasional freeze events and high soil salinities characteristic of the area. Vessel architecture may influence mangrove chilling and salinity tolerance. We surveyed populations of A. germinans throughout the Gulf to determine if vessel architecture was linked to field environmental conditions.We measured vessel density, hydraulically weighted vessel diameter, potential conductance capacity, and maximum tensile fracture stress. At each sampling site we recorded mangrove canopy height and soil salinity, and determined average minimum winter temperature from archived weather records. At a subset of sites, we measured carbon fixation rates using a LI-COR 6400XT Portable Photosynthesis System. Populations of A. germinans from cooler areas (Texas and Louisiana) had narrower vessels, likely reducing the risk of freeze-induced embolisms but also decreasing water conductance capacity. Vessels were also narrower in regions with high soil salinity, includingTexas, USA and tidal flats inVeracruz, Mexico.Vessel density did not consistently vary with temperature or soil salinity. In abiotically stressful areas, A. germinans had a safe hydraulic architecture with narrower vessels that may increase local survival. This safe architecture appears to come at a substantial physiological cost in terms of reduction in conductance capacity and carbon fixation potential, likely contributing to lower canopy heights. The current distribution of A. germinans in the Gulf is influenced by the complex interplay between temperature, salinity, and vessel architecture. Given the plasticity of A. germinans vessel characters, it is likely that this mangrove species will be able to adapt to a wide range of potential future environmental conditions, and continue its expansion in the Gulf of Mexico in response to near-term climate change. [ABSTRACT FROM AUTHOR]

The Gulf Killifish ( Fundulus grandis) is one of the most abundant nekton species in the US Gulf of Mexico (GOM) salt marshes, providing an important trophic link in these systems. Recently, the use of F. grandis as an indicator species of salt marsh health in the region has been suggested because its Atlantic coast congener, the Mummichog ( Fundulus heteroclitus) has filled such a role due to its demonstrated high site fidelity and small-scale movements. Given the similar life histories between species, F. grandis was assumed to exhibit the same type of small-scale movements, although this has not been documented. During summer 2013, we collected and marked 1,719 fish from a northern Gulf of Mexico estuary, recapturing 959 (56 % recapture rate). Of these recaptured fish, only 31 moved from their original tagging location, and of these, 29 moved only 100 m between sites connected by salt marsh. Based on these results, F. grandis appears to exhibit high site fidelity and make only small-scale movements, similar to F. heteroclitus, supporting its role as an indicator species. [ABSTRACT FROM AUTHOR]

Highlights: [•] We modeled the effects of variable vital rates on white shrimp population size. [•] Modest ranges in juvenile survival have greater effects on stock size than fishing. [•] Incorporating factors that regulate juvenile survival will improve stock assessment. [Copyright &y& Elsevier]

This study investigated potential nitrogen fixation, net nitrification, and denitrification responses to short-term crude oil exposure that simulated oil exposure in Juncus roemerianus salt marsh sediments previously impacted following the Deepwater Horizon accident. Temperature as well as crude oil amount and type affected the nitrogen cycling rates. Total nitrogen fixation rates increased 44 and 194 % at 30 °C in 4,000 mg kg tar ball and 10,000 mg kg moderately weathered crude oil treatments, respectively; however, there was no difference from the controls at 10 and 20 °C. Net nitrification rates showed production at 20 °C and consumption at 10 and 30 °C in all oil treatments and controls. Potential denitrification rates were higher than controls in the 10 and 30 ºC treatments but responded differently to the oil type and amount. The highest rates of potential denitrification (12.7 ± 1.0 nmol N g wet h) were observed in the highly weathered 4,000 mg kg oil treatment at 30 °C, suggesting increased rates of denitrification during the warmer summer months. These results indicate that the impacts on nitrogen cycling from a recurring oil spill could depend on the time of the year as well as the amount and type of oil contaminating the marsh. The study provides evidence for impact on nitrogen cycling in coastal marshes that are vulnerable to repeated hydrocarbon exposure. [ABSTRACT FROM AUTHOR]

Abstract: Oil exposure has been shown to be detrimental to several salt marsh plants however little information is available for Juncus roemerianus. Thirty-two mesocosms were established with J. roemerianus sod and replicate marshes were exposed to Louisiana sweet crude oil to test oil dose (6, 12, and 24Lm−2) and weathering (oil weathered for 0days, 3days, and 3weeks). Juncus were monitored following oil exposure for culm survival, photosynthetic rates, and C-assimilation rates. Oil dosage had a significant effect among wetlands with low-dose (6Lm−2) mesocosms having higher culm survival, photosynthetic rates, and C-assimilation rates than medium or high dose wetlands (12 or 24Lm−2). Oil weathering did not elicit significant differences between treated wetlands however full strength wetlands (un-weathered oil) consistently had the lowest culm survivorship, photosynthetic rates, and C-assimilation rates. From our results, J. roemerianus marshes may be very susceptible to oil exposure. [Copyright &y& Elsevier]

Abstract: One and a half years after the worst oil spill in U.S. history, we present the first quantitative assessment on the ecological impact of the spill on the salt marsh habitats along the southeastern Louisiana (LA) coast. This research combined satellite and ground data to quantify the impact of the oil and dispersant on the salt marshes in terms of their photosynthetic capacity and physiological status over a large spatial scale. Two of the most important marsh biophysical characteristics, including distribution of canopy chlorophyll content and above ground green biomass, were monitored across the southeastern LA coast during the salt marsh growing season (May–October) of 2009 (pre-spill) and 2010 (post-spill) in order to compare and isolate the spill impacted areas. The initial assessment showed that there was a significant post-spill increase in areas with reduced biomass and canopy chlorophyll (>400km2) during the 2010 growing season compared to 50–65km2 during the 2009 growing season. Phenological analysis of the post oil-spill data revealed a significant decrease in the magnitude of biomass and canopy chlorophyll during the peak of the 2010 growing season. June was consistently found to be the worst month in terms of salt marsh health across LA over the 2010 phenological cycle followed by the initial signs of recovery along the fringing marsh areas proximal to the shoreline that were first impacted by oil. Interior marsh patches exhibited persistent signs of stress towards the end of the growing season. Extensive reduction in photosynthetic activity was observed during the peak of the growing season, particularly in Plaquemines Parish and St. Bernard Parish. The products generated through this study successfully delineate the critical hotspots of marsh stress so that prioritization of areas needing immediate restoration can be performed. [Copyright &y& Elsevier]

We compared nekton use of prominent habitat types within a lagoonal system of the northeastern Gulf of Mexico (GoM). These habitat types were defined by combinations of structure (cover type) and location (distance from shore) as: Spartina edge (≤1 m from shore), Spartina (3 m from shore); Juncus edge (≤1 m from shore); seagrass located 3, 5, and 20 m from shore; and shallow non-vegetated bottom at various distances from shore. Although seagrass and Spartina edge sites differed little in environmental characteristics, the density and biomass of most abundant taxa, including pink shrimp ( Farfantepenaeus duorarum), were higher in seagrass. Most species within seagrass and Spartina did not differ in abundance or biomass with distance from shore. Our study revealed a shift in peak habitat use in the northeastern GoM to seagrass beds from the pattern observed to the west where nekton is concentrated within shoreline emergent vegetation. [ABSTRACT FROM AUTHOR]

This study examined habitat use patterns of newly settled spotted seatrout Cynoscion nebulosus (Cuvier) across several Gulf of Mexico estuaries. Intensive sampling using an epibenthic sled was conducted in three Texas bays and among three potential habitat types. A long-term data set (1982 to 1997) from the National Marine Fisheries Service was also used to examine C. nebulosus habitat use patterns in both marsh and seagrass-dominated bay systems for broad regional comparisons along the north-western Gulf of Mexico. Vegetated habitat types such as seagrass and marsh supported the highest densities and use was dependent upon availability of particular vegetated habitat types. In laboratory mesocosm experiments, both wild-caught and hatchery-reared C. nebulosus, showed strong selection for structured and vegetated habitat types. These field and laboratory results suggest that seagrass meadows and marshes may be functioning as important habitat for C. nebulosus in Gulf of Mexico, and other habitat types such as oyster reef need further evaluation. [ABSTRACT FROM AUTHOR]

The recent population explosion along the coastal zoneof the southeast United States and the Gulf of Mexicohas accelerated the development rate of waterfrontproperty, and particularly along the Gulf Coast ofMississippi. We compared use of pristine and alteredshoreline habitat by early life-history stages of fishand crustaceans to assess the potential effects ofthis development. Monthly beam trawls were taken at13 sites along shoreline habitats characterized by Juncus/Spartinamarsh, natural beach, and areasaltered by bulkheads and rubble. A total of 52,068fish (n = 48 taxa) and 288,715 crustaceans (n = 24taxa) were collected during a two year study. The mostabundant fish groups included gobiids, sciaenids,clupeids, and engraulids. Crustaceans, excluding thecopepods, were numerically dominated by mysids, bothcaridean and penaeid shrimps, and crabs ( Callinectesspp.). Demersal residents were dominatedby Gobiosoma boscand Palaemonetessp.whereas clupeiformes, sciaenids and penaeid shrimpswere dominant among the nektonic and demersaltransient species. These taxa were least abundantalong stretches of shoreline altered with bulkheads orrubble, and were generally most abundant in shorelinehabitats fringed with Juncus/Spartinagrasses.This general pattern in nekton relative abundanceparallel the low diversity (reciprocal of Simpson'sDominance Index) values adjacent to altered marsh tohigh values adjacent to pristine marsh or beachhabitats, suggesting that habitats adjacent to alteredmarsh sites are less frequently used as nurseryhabitat compared to natural sites. These data supportthe hypothesis that shorelines adjacent to marshhabitat are critical to various life history stages ofecologically- and commercially-important species,illustrate the influence of altering natural marshhabitat on resident/transient nekton, and providequantitative data for resource managers in thecontinued efforts to preserve the complex estuarinemarsh landscape. [ABSTRACT FROM AUTHOR]

The ribbed mussel, Geukensia granosissima , cycles nutrients, contributes to soil stability, and can be a major component of predator-prey communities in salt marshes. Mussels were exposed to the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, and salt marshes remain contaminated eight years later. We hypothesized that the oiled mussels had reduced annual growth, altered population size frequency, and perhaps changed valve morphometrics. We sampled 10 marshes near Port Sulphur, LA, to measure the morphometrics of 133 mussels and their age-specific growth rate, and also the marsh oil content and percent vegetative cover. The relationships between valve weight, length and biomass weight were stable as mussels aged. A Year 1 growth decline from 1994 to 2018 is not easily explained by estuarine acidification, flooding, and temperature rise; freshening of estuarine waters is suggested to be a probable causal factor in the declining growth rate. The average valve length and dry biomass per valve declined with oiling in 2010. A multiple regression equation using the percent cover and oil concentration in 2018 described 70% of the variation in valve length. Sites with the highest oiling had few mussels with 14 annual growth bands and more of the younger mussels compared to sites with the lowest oiling. Valve growth in Year 1 declined for four years after the oil spill and was not compensated by higher growth rates in older mussels. Annual growth was below the amount predicted in a regression equation for the five years after the oil spill. Mussel populations may also have been structured by predators that were also responsive to oiling in subtle ways. [Display omitted] • Age-specific growth of ribbed mussels was measured before and after oil exposure. • Valve length was directly related to % plant cover and indirectly to marsh oiling. • Average valve length, dry biomass and age declined with increased marsh oiling. • Year 1 growth decline with oiling was not compensated by higher growth later. • Estuarine freshening is a probable cause of Year 1 growth decline from 1994 to 2018. The declining mussel growth in marshes was further depressed after oiling from the 2010 Deepwater Horizon oil spill and the population had with fewer older animals. [ABSTRACT FROM AUTHOR]

Black mangroves (Avicennia germinans) are becoming more common along the edges of their range, potentially displacing salt marsh vegetation in transition zones such as the Texas coast in the Gulf of Mexico (USA). Consequences of this shift on trophic interactions within wetland ecosystems are largely unknown. We investigated how increasing mangrove cover might alter predator-prey interactions involving an important consumer in coastal wetlands, blue crabs (Callinectes sapidus), and one of their key prey items, penaeid shrimp (Family Penaeidae). We conducted a series of mesocosm experiments to assess predation rates and prey refuge values in artificial vegetation (AV) matrices simulating flexible marsh grasses (e.g., Spartina patens, Distichlis spicata) and rigid mangrove pneumatophores (aerial root structures). In predation experiments within each of these AV matrices, blue crabs captured 50% fewer penaeid shrimp in the rigid mangrove treatment compared to the flexible marsh treatment, and time between captures was 83% longer among the simulated pneumatophores. In a prey refuge experiment that allowed both predator and prey to move freely among the AV matrices, penaeid shrimp occupied the rigid pneumatophore matrix 30% more often than the grass matrix when blue crabs were present but had no preference when the predator was absent. This study suggests that where A. germinans and marsh grasses co-occur, the mangroves may provide superior refuge for prey items such as penaeid shrimp. Pneumatophores will likely restrict the mobility of predators such as blue crabs, resulting in lower predation efficiency. These results suggest that as mangrove stands continue to increase in cover within mangrove-marsh ecotones, there are likely to be consequences for upper trophic level dynamics. • Blue crabs capture fewer shrimp in a mangrove artificial vegetation (AV) matrix than in a marsh AV matrix. • Blue crab distance and velocity is not different between mangrove and marsh AV matrices. • Shrimp do not prefer an AV matrix in the absence of a predator. • Shrimp prefer mangrove and unvegetated AV matrices over the marsh AV matrix when a predator is present. [ABSTRACT FROM AUTHOR]

Grasshopper herbivory can vary substantially among locations within a salt marsh or among marshes, but its variability along the marsh intertidal gradient (extending from the shoreline to the upland fringing forest) is not well reported. Previous papers have shown that grasshopper herbivory may affect nutrient processes in salt marsh ecosystems, but how such effects are tied up to the intensity of herbivory and how they vary spatially is poorly known. To help address these gaps, we evaluated whether grasshopper herbivory intensity and herbivore abundance together with other plant characteristics (such as total leaf length, plant live and dead biomass, plant nutrient content and plant nutrient standing stocks) varied along the intertidal gradient of two black needlerush marshes in the Northern Gulf of Mexico. Our results show that in one marsh grazing intensity decreased from the shoreline to the forest tree line, but in the other there was similar grazing intensity across the entire intertidal gradient. None of the measured plant characteristics followed the differences in herbivory found along the intertidal gradient and between salt marshes. We also found that, in the salt marsh with decreasing herbivory towards the upland edge, the combination of herbivory, plant nutrient content and plant nutrient standing stocks suggest two different functional zones along the intertidal gradient, one of nutrient availability and recycling near the shoreline and another one of nutrient inmobilization near the upland fringing forest. In concert, the results suggest that grasshopper herbivory intensity may vary along the intertidal gradient in some marshes, but not in others. In turn, spatial differences in herbivory along the intertidal gradient, if they occur, may influence nutrient processes, such as recycling and storage, leading to associated spatial differences in nutrient dynamics in the salt marsh. • Grasshopper herbivory varies along the intertidal gradient in some marshes. • Herbivory variation along the marsh could enhance nutrient recycling zones. • Plant characteristics and nutrient content do not follow the herbivory patterns found. [ABSTRACT FROM AUTHOR]

Over heterogeneous landscapes, organisms and energy move across ecological boundaries and this can have profound effects on overall ecosystem functioning. Both abiotic and biotic factors along habitat boundaries may facilitate or impede key species interactions that drive these energy flows—especially along the land–sea interface. We synthesized the literature detailing estuarine fish diets and habitat characteristics of salt marshes from U.S. East and Gulf coasts to determine patterns and drivers of cross‐boundary trophic transfers at the land–sea interface. Notably, marsh‐platform species (i.e., killifishes, fiddler crabs) appear virtually absent in the diets of transient estuarine fishes in the Gulf of Mexico, while along the South Atlantic and Mid‐Atlantic Bights, marsh‐platform species appear regularly in the diets of many transient estuarine fishes. Tidal amplitude varied across these three biogeographic regions and likely regulates the availability of marsh‐platform species to transient estuarine fishes via both access to the marsh surface for marine predators and emergence of marsh‐resident prey into the adjacent estuary (i.e., higher tidal amplitude increases predator–prey encounter rates). Surprisingly, marsh shoot density was positively correlated with the presence of marsh‐platform species in the diet, but this pattern appears to be mediated by increased tidal amplitude, suggesting the mode and periodicity of abiotic cycles drive diet structure of transient estuarine fishes more so than local habitat structural complexity. Subsequently, these processes likely influence the degree to which "trophic relay" moves energy from the marsh toward the open estuary. Understanding the dynamics that determine energy flows, spatial subsidies, and ultimately, ecosystem‐level productivity, is essential for implementation of holistic ecosystem‐based approaches to conserve and manage complex landscape mosaics. [ABSTRACT FROM AUTHOR]

Prior studies indicated salt marsh periwinkles (Littoraria irrorata) were strongly impacted in heavily oiled marshes for at least 5 years following the Deepwater Horizon oil spill. Here, we detail longer-term effects and recovery over nine years. Our analysis found that neither density nor population size structure recovered at heavily oiled sites where snails were smaller and variability in size structure and density was increased. Total aboveground live plant biomass and stem density remained lower over time in heavily oiled marshes, and we speculate that the resulting more open canopy stimulated benthic microalgal production contributing to high spring periwinkle densities or that the lower stem density reduced the ability of subadults and small adults to escape predation. Our data indicate that periwinkle population recovery may take one to two decades after the oil spill at moderately oiled and heavily oiled sites, respectively., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

We measured the temporal and spatial trajectory of oiling from the April, 2010, Deepwater Horizon oil spill in water from Louisiana's continental shelf, the estuarine waters of Barataria Bay, and in coastal marsh sediments. The concentrations of 28 target alkanes and 43 target polycyclic aromatic hydrocarbons were determined in water samples collected on 10 offshore cruises, in 19 water samples collected monthly one km offshore at 13 inshore stations in 2010 and 2013, and in 16-60 surficial marsh sediment samples collected on each of 26 trips. The concentration of total aromatics in offshore waters peaked in late summer, 2010, at 100 times above the May, 2010 values, which were already slightly contaminated. There were no differences in surface or bottom water samples. The concentration of total aromatics declined at a rate of 73% y -1 to 1/1000th of the May 2010 values by summer 2016. The concentrations inside the estuary were proportional to those one km offshore, but were 10-30% lower. The oil concentrations in sediments were initially different at 1 and 10 m distance into the marsh, but became equal after 2 years. Thus, the distinction between oiled and unoiled sites became blurred, if not non-existent then, and oiling had spread over an area wider than was visible initially. The concentrations of oil in sediments were 100-1000 times above the May 2010 values, and dropped to 10 times higher after 8 years, thereafter, demonstrating a long-term contamination by oil or oil residues that will remain for decades. The chemical signature of the oil residues offshore compared to in the marsh reflects the more aerobic offshore conditions and water-soluble tendencies of the dissolved components, whereas the anaerobic marsh sediments will retain the heavier molecular components for a long time, and have a consequential effect on the ecosystems., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Coastal salt marshes provide the valuable ecosystem service of removing anthropogenic nitrogen (N) via microbially-mediated denitrification. During the 2010 Deepwater Horizon (DWH) spill, oil exposure killed marsh plants in some regions and contributed to rapid compositional shifts in sediment microbial communities, which can impact ecosystem denitrification capacity. Within 3-5 years of the spill, plant biomass and microbial communities in some impacted marshes can recover to a new stable state. The objective of this study was to determine whether marsh recovery 6 years after the DWH oil spill results in subsequent recovery of denitrification capacity. We measured denitrification capacity (isotope pairing technique), microbial 16S rRNA gene composition, and denitrifier abundance (quantitative PCR) at sites subjected to light, moderate, and heavy oiling during the spill that were not targeted by any clean-up efforts. There were no differences in plant belowground biomass, sediment extractable NH 4 + , inorganic nitrogen flux, 16S rRNA composition, 16S rRNA diversity, or denitrifier functional gene (nirS, norB, and nosZ) abundances associated with oiling status, indicating that certain drivers of ecosystem denitrification capacity have recovered or achieved a new stable state six years after the spill. However, on average, denitrification capacities at the moderately and heavily oiled sites were less than 49% of that of the lightly oiled site (27.7 ± 14.7 and 37.2 ± 24.5 vs 71.8 ± 33.8 μmol N m -2 h -1 , respectively). The presence of heavily weathered oiled residue (matched and non-matched for MC252) had no effect on process rates or microbial composition. The loss of function at the moderately and heavily oiled sites compared to the lightly oiled site despite the comparable microbial and environmental factors suggests that oiling intensity plays a role in the long-term recovery of marsh ecosystem services., (Copyright © 2018 Elsevier Ltd. All rights reserved.)