Coastal Alabama Research Articles

FOUR CASES OF SEVERED PEDUNCLES IN BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) ALONG THE ALABAMA COAST.

Alabama (AL) is a hotspot in the Gulf of Mexico (GoM) for human interaction-related cetacean strandings, including harassment, vessel strikes, and fisheries interactions. We examined four bottlenose dolphins (Tursiops truncatus) stranded dead along the AL coast during 2012-2017 with severed peduncles suspected to be related to human interaction (HI). Evidence from each case, including photographs, gross necropsy results, and histopathologic findings when available, was reviewed to determine the mode of severance and whether it contributed to death. In each case, the severance site had smooth, clean edges on at least one side, indicating the use of a sharp instrument to remove the caudal peduncle and flukes. Three cases also had evidence of fisheries interactions, including linear impressions around the rostrum, fins and/or flukes, indicating that these animals may have been entangled in fisheries gear prior to death. Histopathology in one of these cases revealed that the severance occurred perimortem; speculatively, the caudal peduncle and flukes may have been cut off to facilitate removing the dolphin from its entanglement. Although cases of amputation and mutilation are not uncommon globally among stranding reports, few cases have been described and analyzed in the literature. This paper is the first to document and compare multiple cases of severed peduncles with evidence of HI, including fisheries, in the GoM. This case series enhances our understanding of the types of HI occurring in bottlenose dolphins and highlights the need for continued public education, policy, and management to address cases like these.

Warming waters lead to increased habitat suitability for juvenile bull sharks (Carcharhinus leucas)

Coastal ecosystems are highly vulnerable to the impacts of climate change and other stressors, including urbanization and overfishing. Consequently, distributions of coastal fish have begun to change, particularly in response to increasing temperatures linked to climate change. However, few studies have evaluated how natural and anthropogenic disturbances can alter species distributions in conjunction with geophysical habitat alterations, such as changes to land use and land cover (LU/LC). Here, we examine the spatiotemporal changes in the distribution of juvenile bull sharks (Carcharhinus leucas) using a multi-decadal fishery-independent survey of coastal Alabama. Using a boosted regression tree (BRT) modeling framework, we assess the covariance of environmental conditions (sea surface temperature, depth, salinity, dissolved oxygen, riverine discharge, Chl-a) as well as historic changes to LU/LC to the distribution of bull sharks. Species distribution models resultant from BRTs for early (2003–2005) and recent (2018–2020) monitoring periods indicated a mean increase in habitat suitability (i.e., probability of capture) for juvenile bull sharks from 0.028 to 0.082, concomitant with substantial increases in mean annual temperature (0.058°C/yr), Chl-a (2.32 mg/m3), and urbanization (increased LU/LC) since 2000. These results align with observed five-fold increases in the relative abundance of juvenile bull sharks across the study period and demonstrate the impacts of changing environmental conditions on their distribution and relative abundance. As climate change persists, coastal communities will continue to change, altering the structure of ecological communities and the success of nearshore fisheries.

Wooden steps to shallow depths: A new bathymodiolin mussel, Vadumodiolus teredinicola, inhabits shipworm burrows in an ancient submarine forest

Large mussels of the mytilid subfamily Bathymodiolinae are common inhabitants of deep-sea hydrothermal vents and cold seeps, where gill-borne symbionts allow them to utilize energy-rich compounds such as hydrogen sulfide and methane to support abundant growth. This subfamily also includes smaller symbiont-bearing mussels found on deep-sea wood and organic deposits. Phylogenetic analyses suggest that wood association is ancestral to bathymodiolin evolution. This observation led to the “wooden steps” hypothesis, which proposed that wood and other large organic deposits have acted as evolutionary steppingstones, introducing the progenitors of the modern vent and seep Bathymodiolinae to their remote environments. Although this hypothesis implies an evolutionary trajectory from shallow to deep water, no bathymodiolin species that grows and reproduces at depths less than 100 m has yet been formally described. Here we describe a new bathymodiolin genus and species, Vadumodiolus teredinicola, found growing and reproducing at a depth of 18 m in uninhabited shipworm burrows in the remnants of an ancient submerged bald cypress forest off the coast of Alabama. These results demonstrate that the bathymodiolin radiation has not been limited to deep water and that specific association with wood has led to the successful invasion of both deep and shallow marine environments.

Regional β-Diversity of Stream Insects in Coastal Alabama Is Correlated with Stream Conditions, Not Distance among Sites.

β-diversity is often measured over both spatial and temporal gradients of elevation, latitude, and environmental conditions. It is of particular interest to ecologists, as it provides opportunities to test and infer potential causal mechanisms determining local species assemblages. However, studies of invertebrate β-diversity, especially aquatic insects, have lagged far behind other biota. Using partial Mantel tests, we explored the associations between β-diversity of insects found in the coastal streams of Alabama, USA, and stream conditions and distances among sites. β-diversity was expressed using the Sørensen index, βSor, stream conditions were expressed as principal components (PCs), and distances as Euclidean distances (km) among sites. We also investigated the impact of seasonality (fall, summer) and taxonomic resolution (genus, species) on βSor. Regardless of season, βSor was significantly correlated (p < 0.01; r > 0.44) with stream conditions (stream size and water chemistry), while taxonomic resolution had minimal effect on associations between βSor and stream conditions. Distance was never correlated with changes in βSor (p > 0.05). We extended the use of the Sørensen pair-wise index to a multiple-site dissimilarity, βMult, which was partitioned into patterns of spatial turnover (βTurn) and nestedness (βNest). Changes in βMult were driven mostly by turnover rather than nestedness.

Advancing flood damage modeling for coastal Alabama residential properties: A multivariable machine learning approach

Flooding is a global threat and predicting flood risk accurately is vital for effective mitigation and increasing society's awareness of the negative impacts of floods. Over the years, researchers have worked on physical and data-driven models to predict flood damage, striving to improve accuracy and understanding. However, the challenge lies in the scarcity and limitedness of comprehensive datasets needed to develop these models. This study aims to enhance the National Flood Insurance Program (NFIP) claims dataset from Hurricane Katrina in coastal Alabama to make it adequate for multi-variable flood damage assessment. The NFIP claims dataset was combined with the Alabama property dataset, simulated flood hazard information, and property location characteristics. Oversampling techniques are employed to address data imbalance in the datasets. Subsequently, several ensemble machine learning approaches, including random forest, extra tree, extreme gradient boosting, and categorical boosting, are utilized to develop multi-variable flood damage models. The validation of these models demonstrates that extreme gradient boosting performs best, achieving satisfactory results in identifying damaged properties with precision (0.89), recall (0.90), and F1-score (0.90), as well as determining relative damage with R-squared (0.59), root mean squared error (0.21), and Spearman correlation (0.70). Utilizing data oversampling techniques improves the model performance of imbalanced flood damage datasets. Despite the dataset's limitations and data augmentation techniques employed, the model's output explanation based on SHapley Additive exPlanations (SHAP) is constructive as it aligns with the study's expectations regarding the interaction of different features to produce the final results.

Intensification of Hurricane Sally (2020) over the Mississippi River Plume

Abstract Tropical Cyclone (TC) Sally formed on 11 September 2020, traveled through the Gulf of Mexico (GMX), and intensified rapidly before making landfall on the Alabama coast as a devastating category-2 TC with extensive coastal and inland flooding. In this study, using a combination of observations and idealized numerical model experiments, we demonstrate that the Mississippi River plume played a key role in the intensification of Sally near the northern Gulf Coast. As the storm intensified and its translation slowed before landfall, sea surface cooling was reduced along its track, coincident with a pronounced increase in SSS. Further analysis reveals that TC Sally encountered a warm Loop Current eddy in the northern GMX close to the Mississippi River plume. Besides deepening the thermocline, the eddy advected low-salinity Mississippi River plume water into the storm’s path. This resulted in the development of strong upper-ocean salinity stratification, with a shallow layer of freshwater lying above a deep, warm “barrier layer.” Consequently, TC-induced mixing and the associated sea surface cooling were reduced, aiding Sally’s intensification. These results suggest that the Mississippi River plume and freshwater advection by the Loop Current eddies can play an important role in TC intensification near the U.S. Gulf Coast.

Nutrient Removal Potential of Headwater Wetlands in Coastal Plains of Alabama, USA.

Headwater streams drain over 70% of the land in the United States with headwater wetlands covering 6.59 million hectares. These ecosystems are important landscape features in the southeast United States, with underlying effects on ecosystem health, water yield, nutrient cycling, biodiversity, and water quality. However, little is known about the relationship between headwater wetlands' nutrient function (i.e., nutrient load removal and removal efficiency ) and their physical characteristics. Here, we investigate this relationship for 44 headwater wetlands located within the Upper Fish River watershed (UFRW) in coastal Alabama. To accomplish this objective, we apply the process-based watershed model SWAT (Soil and Water Assessment Tool) to generate flow and nutrient loadings to each study wetland and subsequently quantify the wetland-level nutrient removal efficiencies using the process-based wetland model WetQual. Results show that the calculated removal efficiencies of the headwater wetlands in the UFRW are 75-84% and 27-35% for nitrate and phosphate , respectively. The calculated nutrient load removals are highly correlated with the input loads, and the estimated shows a significant decreasing trend with increased input loadings. The relationship between and wetland physical characteristics such as area, volume, and residence time is statistically insignificant (p > 0.05), while for , the correlation is positive and statistically significant (p < 0.05). On the other hand, flashiness (flow pulsing) and baseflow index (fraction of inflow that is coming from baseflow) have a strong effect on removal but not on removal. Modeling results and statistical analysis point toward denitrification and plant uptake as major removal mechanisms, whereas plant uptake, diffusion, and settling of sediment-bound P were the main mechanisms for removal. Additionally, the computed nutrient is higher during the driest year of the simulated period compared to during the wettest year. Our findings are in line with global-level studies and offer new insights into wetland physical characteristics affecting nutrient removal efficiency and the importance of headwater wetlands in mitigating water quality deterioration in coastal areas. The regression relationships for and load removals in the selected 44 wetlands are then used to extrapolate nutrient load removals to 348 unmodeled non-riverine and non-riparian wetlands in the UFRW (41% of UFRW drains to them). Results show that these wetlands remove 51-61% of the and 5-10% of the loading they receive from their respective drainage areas. Due to geographical proximity and physiographic similarity, these results can be scaled up to the coastal plains of Alabama and Northwest Florida.

Assessment of phthalic acid esters plasticizers in sediments of coastal Alabama, USA: Occurrence, source, and ecological risk

Considering the ubiquitous occurrences and ecotoxicity of phthalates (PAEs), it is essential to understand their sources, distribution, and associated ecological risks of PAEs in sediments to assess the environmental health of estuaries and support effective management practices. This study provides the first comprehensive dataset on the occurrence, spatial variation, inventory, and potential ecological risk assessment of PAEs in surface sediments of commercially and ecologically significant estuaries in the southeastern United States, Mobile Bay and adjoining eastern Mississippi Sound. Fifteen PAEs were widely detected in the sediments of the study region, with total concentrations varying between 0.02 and 3.37 μg/g. The dominance of low-molecular-weight (LMW) PAEs (DEP, DBP and DiBP) relative to high-molecular-weight (HMW) PAEs (DEHP, DOP, DNP) indicates that residential activities have stronger impacts than industrial activities on PAE distributions. The total PAE concentrations displayed an overall decreasing trend with increasing bottom water salinity, with the maximum concentrations occurring near river mouths. These observations suggest that river inputs were an important pathway by which PAEs were transported to the estuary. Linear regression models identified sediment adsorption (measured by total organic carbon and median grain size) and riverine inputs (measured by bottom water salinity) as significant predictors for the concentrations of LMW and HMW PAEs. Estimated 5-year total inventories of sedimentary PAEs in Mobile Bay and the eastern Mississippi Sound were 13.82 tons and 1.16 tons, respectively. Risk assessment calculations suggest that LMW PAEs posed a medium-to-high risk to sensitive aquatic organisms, and DEHP posed a low or negligible risk to the aquatic organisms. The results of this study provide important information needed for establishing and implementing effective practices for monitoring and regulating plasticizer pollutants in estuaries.

Detection of invasive plants using NAIP imagery and airborne LiDAR in coastal Alabama and Mississippi, USA

Invasive plants have imposed severe threats to native ecosystems worldwide. Triadica sebifera (Tallow tree) and Ligustrum sinense (Chinese privet) are among the most prolific invasive species in the southern United States (US) that needs urgent assessment to protect coastal ecosystems. The lack of spatially explicit assessments of these invasives, coupled with the increasing availability of high-resolution remotely sensed data, represents an opportunity to produce a distribution map for subsequent monitoring. The overall goal of this study was to develop spatially comprehensive maps of Tallow tree and Chinese privet in ecologically sensitive coastal regions, where both invasives have become well established. The study was conducted in three coastal sites within Alabama and Mississippi: (1) Mobile Tensaw River Delta, (2) Bon Secour National Wildlife Refuge, and (3) Mississippi Sandhill Crane National Wildlife Refuge. We implemented three image classification methods, representing unsupervised, supervised, and machine learning techniques, respectively: (1) ISODATA, (2) Maximum Likelihood (ML), and (3) Random Forest (RF). For each classification, a 1 m National Agriculture Imagery Program (NAIP) orthoimage was first examined, then integrated with vegetation structure and topography parameter derived from airborne light detection and ranging (LiDAR). The maximum Overall Accuracy (OA) of 87.5% was obtained using RF model with NAIP stacked image integrated with LiDAR derived variables. Overall, findings highlight the potential for accurately characterizing both Tallow tree and Chinese privet using readily available remote sensing data. Mapped products from this study represent a spatially comprehensive baseline inventory of crucial invasive species and will serve to inform the development of a framework for broader-scale mapping and monitoring efforts.

Assessing habitat enhancement by living shoreline restoration: exploring potential caveats of nekton community metrics

Living shorelines (LS) are a nature‐based restoration technique that aims to stabilize shorelines while enhancing multiple ecosystem services. In particular, LS are frequently promoted as beneficial for enhancing essential coastal habitats for fish and mobile crustaceans (nekton). In this study, we aimed to assess the effects of LS on nekton habitat across eight LS restoration sites in coastal Alabama, U.S.A., by applying widely‐used community metrics. Nekton abundance, species richness, evenness, and diversity tended to be higher in LS and adjacent unrestored control sites than along nearby hardened shorelines. Community metrics showed no clear effect of LS compared to their adjacent controls, with substantial among‐site variation masking any restoration effect. While this may suggest an ecological equivalence between restored and control sites, there are other possible interpretations; that a lack of difference reflects sampling the same populations at nearby control and restored sites, that differences do exist but sampling effort was insufficient to detect them, or that community metrics may be too insensitive for comparing the effects of various restoration approaches on nekton habitat quality. Further exploration of individual‐based metrics such as growth and condition of key species is warranted, as these may be more sensitive for assessing restoration outcomes and guiding future project designs.

Dominant attitudes and values toward wildlife and the environment in coastal Alabama

AbstractSurveys assessing attitudes and values about the environment can help predict human behavior toward wildlife and develop effective conservation goals alongside local communities. Coastal Alabama, in the southeastern United States, is a hotspot for biodiversity and endemism and needs protection. Land and wildlife management practices in Alabama have moved from indigenous‐led, which is more in harmony with the environment, to larger‐scale exploitative uses for agriculture and plantations. We therefore predicted that a large proportion of the population has a dominant view of the environment in which land and wildlife are primarily for human benefit. To test this hypothesis, we surveyed over 1300 residents in Mobile and Baldwin counties—the two southernmost counties in Alabama—to assess attitudes toward local vertebrate wildlife, knowledge of the region's biodiversity, and whether individuals value protected areas where they live and/or work. As hunting is generally considered a dominant behavior, we used self‐identified hunters versus non‐hunters to examine the relationship between humans and the environment. Overall, hunters would kill or kill to eat more often than non‐hunters, and would kill even when it is not for food. Furthermore, regardless of hunting status, most participants in our survey would kill a snake, indicating that targeted environmental education is needed for this group. Both hunters and non‐hunters, independently of demographic differences including education and income levels, were not familiar with the especially rich biodiversity of the area and would not be willing to invest money to protect it. Our results indicate that targeted education about the unique and rich biodiversity of southern Alabama compared to the rest of the United States is needed to support successful environmental management, conservation actions, and local participation.

Two new natural Sarracenia hybrids from the Gulf Coast

Sarracenia ×gordonii and Sarracenia ×mellichampii, two new natural Sarracenia hybrids from the Gulf Coast of Mississippi and Alabama are described.

Live-Dead Shifts in Molluscan Functional Diversity in Coastal Alabama

Abiotic and biotic environmental factors shape species behavioral, physiological, and morphological traits. Shifts in the diversity of these functional traits therefore can serve as an indicator of spatial and temporal changes in environmental conditions. In recent centuries, the delivery of nutrients to coastal ecosystems has increased markedly through changing waste management and land-use practices. Nutrient enrichment has increased rates of primary productivity, resulting in greater organic accumulation on the seafloor and the development of hypoxic conditions in some areas, due to the aerobic decomposition of phytoplankton blooms. Anthropogenic eutrophication and associated hypoxia have been monitored annually in the northern Gulf of Mexico for over four decades, with an emphasis on areas surrounding the Mississippi River Delta. To further understand how anthropogenic eutrophication affects functional diversity in benthic marine communities, we collected live and dead assemblages of bivalve mollusks from surficial sediments at five stations along the -20 meters isobath in coastal Alabama. Bivalves were categorized into functional groups using information about their mobility, fixation, feeding type, substrate preference, and body size. Consistent with our hypotheses, preliminary results indicate a temporal shift from benthic communities dominated primarily by epifaunal and infaunal suspension-feeding species to communities characterized primarily by deposit feeders, many of which dwell on the seafloor surface. Ongoing analyses will help identify the functional traits that are most sensitive to these changing environmental conditions. Understanding functional diversity shifts in the recent past can provide insight into how anthropogenic eutrophication may further impact benthic marine ecosystems in the future.

Shell Microstructure as an Indicator of Changing Environmental Conditions in Coastal Oceans

Ocean ecosystems are undergoing pronounced changes in temperature and chemistry. Biomineralizing animals, such as mollusks, that produce calcium carbonate shells can be sensitive to these changes, and this may be reflected in the microstructure of their shells. Shell microstructure potentially offers conservation paleobiologists an additional tool for assessing spatiotemporal changes in environmental conditions resulting from human activities. Previous work suggests that environmental factors, such as temperature and pH, can affect how mollusks build their shells. Certain mollusks continuously lay down tablets of nacre on the interior of their shells, and the thickness of these tablets may reflect the temperature of the environment in which the organism lived. We have been investigating spatial and temporal variation in tablet thickness in two groups of marine mollusks. Our first case study focuses on a variety of present-day abalone species along a temperature gradient. Data were collected from individuals raised in aquaculture at controlled temperatures, as well as wild-grown individuals from different latitudes in the Pacific Ocean. Our second case study focuses on the marine bivalve Nucula proxima from the northern Gulf of Mexico. Live and dead Nucula proxima specimens were collected from 20 meters water depth offshore Louisiana and Alabama; radiocarbon analyses indicate that these specimens represent both present-day and pre-Industrial populations. Our preliminary results show: 1) little variation in tablet thickness among abalone grown in aquaculture at different temperatures, suggesting that fine scale variation in temperature has little effect on abalone microstructure; and 2) an increase in tablet thickness during the past 250 years for N. proxima offshore Louisiana, but little change in N. proxima microstructure in coastal Alabama over past centuries.

Life Histories Vary with Primary Productivity in the Northern Gulf of Mexico

Human activities have increased nutrient delivery to aquatic ecosystems around the world, spurring primary productivity, and leading to the establishment and expansion of oxygen-limited “dead zones.” How will marine animals respond to these changing conditions? To address that question, we take a space-for-time approach and compare the traits of different marine invertebrates along a primary productivity gradient in the northern Gulf of Mexico. Previous studies have found that life history traits can be sensitive to prevailing environmental conditions. Using Holocene death assemblages collected from -20 meters offshore Alabama and Florida, we test the hypothesis that bivalve egg size, and bryozoan reproductive mode, vary with primary productivity. Based on previous studies, we expect populations in areas with an abundance of food to exhibit the following characteristics: 1) cupuladriid bryozoans will exhibit greater frequencies of clonal to aclonal reproduction; and 2) bivalves will produce smaller eggs due to greater juvenile survivorship and fecundity selection. We found that Discoporella depressa colonies show low frequencies of clonal reproduction overall, but that percent clonality was greater in coastal Alabama than Florida. Cupuladria colonies showed higher proportions of clonal reproduction, whereas Reussirella doma colonies exhibited exclusively aclonal reproduction. Egg size is positively correlated with the earliest stage of larval shell growth (PI size) in marine bivalves. Nucula proxima larval shell size varied inversely with primary productivity; larval shells were larger in Florida than Alabama. Preliminary live-dead results in both regions show limited evidence of change over time, in contrast with previous analyses of other bivalve species in the region. These space-for-time case studies highlight ways in which benthic marine invertebrates may respond to future anthropogenic driven changes in primary production in the coastal ocean.

Stand and tree characteristics influence damage severity after a catastrophic hurricane disturbance

Catastrophic wind disturbances can greatly impact the economic and ecological values of working forests worldwide. For example, Hurricane Michael caused severe economic damage in 2018 to commercial loblolly (Pinus taeda L.) and slash (Pinus elliotti Engelm.) planted pine stands in the southeastern U.S. This project examined the relative importance of prior management activities, stand characteristics, and soil and terrain attributes in predicting stand damage from a catastrophic hurricane event. We assembled data from land managers in coastal Alabama, the Florida panhandle, and South Georgia, on percent loss of trees after Hurricane Michael in over 400 stands, along with stand management history, and stand characteristics. Digital elevation models were utilized to determine terrain and hydrological characteristics of the landscape including aspect, channel distance, elevation, LS factor (slope and length steepness factor), slope angle, slope position, terrain ruggedness index, topographic wetness index, and wind exposition index. Random forest models were used to determine the relative accuracy of windspeed, management history, stand characteristics, and soil and terrain attributes in predicting stand damage. From the variables evaluated, stand density (as described by trees per acre), and tree height (as described by the average height of dominant and co-dominant trees) were among the most influential characteristics in predicting damage severity along with windspeed and linear distance from the coast. Stands with dominant heights > 14 m, trees per acre < 600 (trees per hectare < 1,483), and within 50 km of the coast were the most likely to experience severe damage. Topographic wetness index was the most influential terrain characteristic, with sands in wetter soils more likely to experience more severe damage. Recently thinned stands were slightly more vulnerable to severe damage. Results from this study can be used to develop vulnerability profiles for commercial pine stands in the coastal plain region in the southern U.S. region.

Assessment of Living Shorelines for Restoring Fish Habitats: A Case Study from Coastal Alabama

Assessment of Living Shorelines for Restoring Fish Habitats: A Case Study from Coastal Alabama

Oyster Reef Restoration May Influence Local Sediment Geochemistry Prior to Introduction of Live Oysters

Oyster reefs provide crucial ecosystem services, but their populations are declining worldwide. Oyster reef restoration efforts are underway in many regions, including the Gulf Coast of the United States, where the intertidal oyster populations of the eastern oyster, Crassostrea virginica, have experienced significant declines. A novel method of restoration aimed at decreasing oyster mortality from predators through induction of predatory defenses has been implemented in coastal Alabama. The first step in this novel oyster reef restoration method is the deployment of a base layer of uninhabited oyster shells directly on the sediment prior to the introduction of live oysters. This study evaluated the impacts of the first step of this novel method of restoration, construction of the reef structure, on local sediment physicochemical characteristics. Results indicate that the vertical structure of the oyster reef affects sediment grain size and physicochemical properties. After 47 days, sediment pH increased from 8.29 ± 0.04 to 8.86 ± 0.03 with a concomitant increase in calcium carbonate from 0.509 ± 0.021 % to 0.818 ± 0.112 %. Despite many positive geochemical effects of oyster reef restoration being mediated by the presence of live oysters, the increased pH and calcium carbonate demonstrated herein represent more ideal conditions for oyster growth and survivability, potentially increasing the long-term efficacy of oyster reef restoration via this method.

Field measurements of boat wake attenuation in salt marshes of coastal Alabama

Four pressure gauges were deployed along natural marsh transects in Mobile, Alabama, to assess the ability of marsh vegetation to reduce the height and energy of oncoming boat wakes. The present study explores the influence of vegetation species, marsh density, wave height, wave frequency, and seabed terrain on the degree of attenuation. The pressure data were translated into instantaneous free surface position and wave height measurements, and the influence of shoaling and wave breaking was accounted for. It was found that attenuation is nonlinear, with an increased concentration of wave height and energy loss occurring in the first few meters, and that the seabed plays a significant role in wave transformation. The highest 1% of wave heights was most effectively reduced due to the combined influence of terrain and vegetation while the mean wave heights were the least reduced wave height statistic. Determination of accurate decay coefficients was complicated by the high degree of variability observed within the study. The results showed a correlation between wave frequency and energy dissipation, with the most substantial loss occurring at the peak frequency. Collectively, the findings highlight the variability between marsh sites and reinforce the recommendation that there be further exploration of wave energy attenuation by marsh grasses.

Mercury biomagnification in a coastal Louisiana food web following the 2010 Deepwater Horizon oil spill

The estuarine environments surrounding coastal Louisiana create favorable conditions for microbially mediated mercury (Hg) methylation and subsequent bioaccumulation by biota. In 2010, the Deepwater Horizon (DWH) oil spill released large amounts of oil which, despite having low Hg concentrations, had the potential to influence methylmercury (MeHg) bioavailability in the coastal zone. To explore this possibility, we assessed Hg concentrations and trophodynamics in the coastal Louisiana food web prior to and immediately following the DWH oil spill and compared these metrics with an adjacent coastal ecosystem in the northern Gulf of Mexico. We found no differences in MeHg concentrations between oysters collected in years prior to the spill (1986–2007) and those collected during or in the months immediately after the spill (May to December 2010). When comparing tissue MeHg concentrations and carbon and nitrogen stable isotope values across 13 species of bivalves, shrimp, crabs, fishes, and birds we found evidence of significant biomagnification within the coastal Louisiana food web driven by species’ trophic position and their use of differing basal carbon sources. In addition, Hg trophodynamics also differed between two adjacent coastal ecosystems, post-spill coastal Louisiana (2010) and pre-spill coastal Alabama (2008–2009). While there was a higher trophic magnification factor in coastal Louisiana relative to coastal Alabama, food web baseline MeHg concentrations were higher in coastal Alabama. The high degree of biomagnification in coastal Louisiana, and significant regional variation, underscores the need to monitor Hg trophodynamics over space and time to better evaluate the short and long-term ecological consequences of events like the DWH oil spill.