Barataria Bay Research Articles

Response of salt marshes to oiling from the Deepwater Horizon spill: Implications for plant growth, soil surface-erosion, and shoreline stability

We investigated the initial impacts and post spill recovery of salt marshes over a 3.5-year period along northern Barataria Bay, LA, USA exposed to varying degrees of Deepwater Horizon oiling to determine the effects on shoreline-stabilizing vegetation and soil processes. In moderately oiled marshes, surface soil total petroleum hydrocarbon concentrations were ~70mgg−1 nine months after the spill. Though initial impacts of moderate oiling were evident, Spartina alterniflora and Juncus roemerianus aboveground biomass and total live belowground biomass were equivalent to reference marshes within 24–30months post spill. In contrast, heavily oiled marsh plants did not fully recover from oiling with surface soil total petroleum hydrocarbon concentrations that exceeded 500mgg−1 nine months after oiling. Initially, heavy oiling resulted in near complete plant mortality, and subsequent recovery of live aboveground biomass was only 50% of reference marshes 42months after the spill. Heavy oiling also changed the vegetation structure of shoreline marshes from a mixed Spartina–Juncus community to predominantly Spartina; live Spartina aboveground biomass recovered within 2–3years, however, Juncus showed no recovery. In addition, live belowground biomass (0–12cm) in heavily oiled marshes was reduced by 76% three and a half years after the spill. Detrimental effects of heavy oiling on marsh plants also corresponded with significantly lower soil shear strength, lower sedimentation rates, and higher vertical soil-surface erosion rates, thus potentially affecting shoreline salt marsh stability.

Employing ecosystem models and geographic information systems (GIS) to investigate the response of changing marsh edge on historical biomass of estuarine nekton in Barataria Bay, Louisiana, USA

Louisiana's coastal ecosystem has a long historical record of productive fisheries. Even in light of the multiple perturbations experienced in this region, fish and shellfish landings have remained stable or increasing. These disturbances have resulted in many unforeseen ecological consequences; one such consequence is the loss of marsh vegetation in southern Louisiana (LA). Marsh habitats are thought to function as nursery habitats for post-larval and juvenile fishes, providing both refuge from predation and increased foraging opportunities. As the loss of marsh appeared to have a null effect on fish and shellfish yields, there evolved a hypothesis that described a positive effect on nekton production; increasing marsh edge distance during marsh degradation provides a potential short-term increase in marsh access for organisms. Here we used Geographic Information System (GIS) data to determine the patterns of marsh loss over a 10 year period and to create marsh edge maps for further analysis in an ecosystem model. We used the ecosystem model Ecopath with Ecosim and Ecospace (EwE) to determine if a suitable response mechanism between estuarine organisms and marsh edge distance could be developed. The scenario analysis of multiple theoretical response functions showed Ecospace's ability to model changing habitat and environmental variables over time and space. More specifically, while the results of this modeling effort revealed species-specific responses to marsh edge, the association between nekton and marsh edge may not be as tightly coupled as once thought in coastal LA.

Reproductive outcome and survival of common bottlenose dolphins sampled in Barataria Bay, Louisiana, USA, following the Deepwater Horizon oil spill.

Common bottlenose dolphins (Tursiops truncatus) inhabit bays, sounds and estuaries across the Gulf of Mexico. Following the Deepwater Horizon oil spill, studies were initiated to assess potential effects on these ecologically important apex predators. A previous study reported disease conditions, including lung disease and impaired stress response, for 32 dolphins that were temporarily captured and given health assessments in Barataria Bay, Louisiana, USA. Ten of the sampled dolphins were determined to be pregnant, with expected due dates the following spring or summer. Here, we report findings after 47 months of follow-up monitoring of those sampled dolphins. Only 20% (95% CI: 2.50–55.6%) of the pregnant dolphins produced viable calves, as compared with a previously reported pregnancy success rate of 83% in a reference population. Fifty-seven per cent of pregnant females that did not successfully produce a calf had been previously diagnosed with moderate–severe lung disease. In addition, the estimated annual survival rate of the sampled cohort was low (86.8%, 95% CI: 80.0–92.7%) as compared with survival rates of 95.1% and 96.2% from two other previously studied bottlenose dolphin populations. Our findings confirm low reproductive success and high mortality in dolphins from a heavily oiled estuary when compared with other populations. Follow-up studies are needed to better understand the potential recovery of dolphins in Barataria Bay and, by extension, other Gulf coastal regions impacted by the spill.

Population ecology of the gulf ribbed mussel across a salinity gradient: recruitment, growth and density

Benthic intertidal bivalves play an essential role in estuarine ecosystems by contributing to habitat provision, water filtration, and promoting productivity. As such, changes that impact population distributions and persistence of local bivalve populations may have large ecosystem level consequences. Recruitment, growth, mortality, population size structure and density of the gulf coast ribbed mussel, Geukensia granosissima, were examined across a salinity gradient in southeastern Louisiana. Data were collected along 100‐m transects at interior and edge marsh plots located at duplicate sites in upper (salinity ~4 psu), central (salinity ~8 psu) and lower (salinity ~15 psu) Barataria Bay, Louisiana, U.S.A. Growth, mortality and recruitment were measured in established plots from April through November 2012. Mussel densities were greatest within the middle bay (salinity ~8) regardless of flooding regime, but strongly associated with highest stem densities of Juncus roemerianus vegetation. Mussel recruitment, growth, size and survival were significantly higher at mid and high salinity marsh edge sites as compared to all interior marsh and low salinity sites. The observed patterns of density, growth and mortality in Barataria Bay may reflect detrital food resource availability, host vegetation community distribution along the salinity gradient, salinity tolerance of the mussel, and reduced predation at higher salinity edge sites.

Significant spatial variability of bioavailable PAHs in water column and sediment porewater in the Gulf of Mexico 1year after the Deepwater Horizon oil spill.

One year after the Deepwater Horizon oil spill accident, semipermeable membrane devices (SPMDs) and polyethylene devices (PEDs) were deployed in wetland areas and coastal areas of the Gulf of Mexico (GOM) to monitor polycyclic aromatic hydrocarbons (PAHs). The measured PAH levels with the PEDs in coastal areas were 0.05-1.9ng/L in water and 0.03-9.7ng/L in sediment porewater. With the SPMDs, the measured PAH levels in wetlands (Barataria Bay) were 1.4-73ng/L in water and 3.3-107ng/L in porewater. The total PAH concentrations in the coastal areas were close to the reported baseline PAH concentrations in GOM; however, the total PAH concentrations in the wetland areas were one or two orders of magnitude higher than those reported in the coastal areas. In light of the significant spatial variability of PAHs in the Gulf's environments, baseline information on PAHs should be obtained in specific areas periodically.

Seasonal Variation of Colored Dissolved Organic Matter in Barataria Bay, Louisiana, Using Combined Landsat and Field Data

Coastal bays, such as Barataria Bay, are important transition zones between the terrigenous and marine environments that are also optically complex due to elevated amounts of particulate and dissolved constituents. Monthly field data collected over a period of 15 months in 2010 and 2011 in Barataria Bay were used to develop an empirical band ratio algorithm for the Landsat-5 TM that showed a good correlation with the Colored Dissolved Organic Matter (CDOM) absorption coefficient at 355 nm (ag355) (R2 = 0.74). Landsat-derived CDOM maps generally captured the major details of CDOM distribution and seasonal influences, suggesting the potential use of Landsat imagery to monitor biogeochemistry in coastal water environments. An investigation of the seasonal variation in ag355 conducted using Landsat-derived ag355 as well as field data suggested the strong influence of seasonality in the different regions of the bay with the marine end members (lower bay) experiencing generally low but highly variable ag355 and the freshwater end members (upper bay) experiencing high ag355 with low variability. Barataria Bay experienced a significant increase in ag355 during the freshwater release at the Davis Pond Freshwater Diversion (DPFD) following the Deep Water Horizon oil spill in 2010 and following the Mississippi River (MR) flood conditions in 2011, resulting in a weak linkage to salinity in comparison to the other seasons. Tree based statistical analysis showed the influence of high river flow conditions, high- and low-pressure systems that appeared to control ag355 by ~28%, 29% and 43% of the time duration over the study period at the marine end member just outside the bay. An analysis of CDOM variability in 2010 revealed the strong influence of the MR in controlling CDOM abundance in the lower bay during the high flow conditions, while strong winds associated with cold fronts significantly increase CDOM abundance in the upper bay, thus revealing the important role these events play in the CDOM dynamics of the bay.

Chemical and histological comparisons between Brevoortia sp. (menhaden) collected in fall 2010 from Barataria Bay, LA and Delaware Bay, NJ following the DeepWater Horizon (DWH) oil spill

Body burdens of PAHs were compared to histological effects in menhaden (Family: Clupeidae, Genus: Brevoortia) collected in fall 2010 from Barataria Bay, LA (BBLA) and Delaware Bay, NJ (DBNJ). Barataria Bay was heavily oiled during the DeepWater Horizon (DWH) oil spill, while Delaware Bay although urbanized had no reported recent oil spills. GCMS analyses of pre-spill 2009, BBLA and DBNJ fish found predominantly C2/C3 phenanthrene (1.28–6.52 ng/mg). However, BBLA also contained five higher molecular weight PAHs (0.06–0.34 ng/mg DW). Fluorescent aromatic compound spectroscopy (FACS) of gastrointestinal (GI) tract tissue showed statistically higher levels of hydroxypyrene-like PAHs in DBNJ than BBLA fish. Histopathologic lesions were more prevalent in BBLA than DBNJ fish. The lesion prevalence (gill, trunk kidney, epidermis, stomach) in the BBLA menhaden were significantly higher and more severe than observed in the DBNJ menhaden. Reversible lesions included gill lamellar hyperplasia, adhesions, edema, and epidermal hyperplasia. The increased pigmented macrophage centers were indicative of activated macrophages responding to connective tissue damage or other antigens. The liver hepatic necrosis and renal tissue mineralization may well have undergone repair, but damage to the kidney nephrons and hepatic/biliary regions of the liver would be slower to resolve and apparently remained after elimination of PAHs. Therefore, a direct cause and effect between DWH oil spill and increased lesion prevalence in BBLA menhaden could not be established.

Detection of polycyclic aromatic hydrocarbons (PAHs) in raw menhaden fish oil using fluorescence spectroscopy: Method development.

Raw menhaden fish oil was developed for biomonitoring polycyclic aromatic hydrocarbons (PAHs) using fluorescence spectroscopy. Menhaden (Genus Brevoortia) were collected in 2010 and/or 2011 from Delaware Bay, New Jersey, USA; James River, Virginia, USA; Vermillion Bay, Louisiana, USA (VBLA); and Barataria Bay, Louisiana, USA (BBLA). Barataria Bay, Louisiana received heavy oiling from the Deepwater Horizon oil spill. Method development included determining optimal wavelengths for PAH detection, fish oil matrix interferences, and influence of solvent concentration on extraction. Results showed that some fish oils contained high molecular weight PAH-like compounds in addition to other fluorescent compounds such as albumin and vitamin A and vitamin E. None of these naturally occurring compounds interfered with detection of high molecular weight PAHs. However, data suggested that the lipid component of fish oil was altering fluorescence spectra by supporting the formation of PAH excimers. For example, the most intense excitation wavelength for hydroxypyrene shifted from Ex285/Em430 to Ex340/Em430. Comparison of Deepwater Horizon crude oil and fish oil spectra indicated that some fish oils contained crude oil-like PAHs. Using wavelengths of Ex360/Em430, fish oil concentrations were calculated as 3.92 μg/g, 0.61 μg/g, and 0.14 μg/g for a Delaware Bay sample, BBLA 2011, and VBLA 2011, respectively. Overall, these results supported using menhaden fish oil to track PAH exposures spatially and temporally.

Oil Biodegradation and Oil-Degrading Microbial Populations in Marsh Sediments Impacted by Oil from the Deepwater Horizon Well Blowout.

To study hydrocarbon biodegradation in marsh sediments impacted by Macondo oil from the Deepwater Horizon well blowout, we collected sediment cores 18-36 months after the accident at the marshes in Bay Jimmy (Upper Barataria Bay), Louisiana, United States. The highest concentrations of oil were found in the top 2 cm of sediment nearest the waterline at the shorelines known to have been heavily oiled. Although petroleum hydrocarbons were detectable, Macondo oil could not be identified below 8 cm in 19 of the 20 surveyed sites. At the one site where oil was detected below 8 cm, concentrations were low. Residual Macondo oil was already highly weathered at the start of the study, and the concentrations of individual saturated hydrocarbons and polycyclic aromatic hydrocarbons continued to decrease over the course of the study due to biodegradation. Desulfococcus oleovorans, Marinobacter hydrocarbonoclasticus, Mycobacterium vanbaalenii, and related mycobacteria were the most abundant oil-degrading microorganisms detected in the top 2 cm at the oiled sites. Relative populations of these taxa declined as oil concentrations declined. The diversity of the microbial community was low at heavily oiled sites compared to that of the unoiled reference sites. As oil concentrations decreased over time, microbial diversity increased and approached the diversity levels of the reference sites. These trends show that the oil continues to be biodegraded, and microbial diversity continues to increase, indicating ongoing overall ecological recovery.

Seasonal variation in the skin transcriptome of common bottlenose dolphins (Tursiops truncatus) from the northern Gulf of Mexico.

As long-lived predators that integrate exposures across multiple trophic levels, cetaceans are recognized as sentinels for the health of marine ecosystems. Their utility as sentinels requires the establishment of baseline health parameters. Because cetaceans are protected, measurements obtained with minimal disruption to free ranging animals are highly desirable. In this study we investigated the utility of skin gene expression profiling to monitor health and contaminant exposure in common bottlenose dolphins (Tursiops truncatus). Remote integument biopsies were collected in the northern Gulf of Mexico prior to the Deepwater Horizon oil spill (May 2010) and during summer and winter for two years following oil contamination (2010-2011). A bottlenose dolphin microarray was used to characterize the skin transcriptomes of 94 individuals from three populations: Barataria Bay, Louisiana, Chandeleur Sound, Louisiana, and Mississippi Sound, Mississippi/Alabama. Skin transcriptomes did not differ significantly between populations. In contrast, season had a profound effect on gene expression, with nearly one-third of all genes on the array differing in expression between winter and the warmer seasons (moderated T-test; p<0.01, fold-change≥1.5). Persistent organic pollutants (POPs) in blubber changed concurrently, reaching >two-fold higher concentrations in summer compared to winter, due to a seasonal decrease in blubber thickness and loss of stored lipid. However, global gene expression did not correlate strongly with seasonally changing contaminant concentrations, most likely because the refractory, lipid-stored metabolites are not substrates for phase I or II xenobiotic detoxification pathways. Rather, processes related to cell proliferation, motility, and differentiation dominated the differences in expression in winter and the warmer seasons. More subtle differences were seen between spring and summer (1.5% of genes differentially expressed). However, two presumed oil-exposed animals from spring presented gene expression profiles more similar to the summer animals (presumed exposed) than to other spring animals. Seasonal effects have not previously been considered in studies assessing gene expression in cetaceans, but clearly must be taken into account when applying transcriptomic analyses to investigate their contaminant exposure or health status.

Adrenal Gland and Lung Lesions in Gulf of Mexico Common Bottlenose Dolphins (Tursiops truncatus) Found Dead following the Deepwater Horizon Oil Spill.

A northern Gulf of Mexico (GoM) cetacean unusual mortality event (UME) involving primarily bottlenose dolphins (Tursiops truncatus) in Louisiana, Mississippi, and Alabama began in February 2010 and continued into 2014. Overlapping in time and space with this UME was the Deepwater Horizon (DWH) oil spill, which was proposed as a contributing cause of adrenal disease, lung disease, and poor health in live dolphins examined during 2011 in Barataria Bay, Louisiana. To assess potential contributing factors and causes of deaths for stranded UME dolphins from June 2010 through December 2012, lung and adrenal gland tissues were histologically evaluated from 46 fresh dead non-perinatal carcasses that stranded in Louisiana (including 22 from Barataria Bay), Mississippi, and Alabama. UME dolphins were tested for evidence of biotoxicosis, morbillivirus infection, and brucellosis. Results were compared to up to 106 fresh dead stranded dolphins from outside the UME area or prior to the DWH spill. UME dolphins were more likely to have primary bacterial pneumonia (22% compared to 2% in non-UME dolphins, P = .003) and thin adrenal cortices (33% compared to 7% in non-UME dolphins, P = .003). In 70% of UME dolphins with primary bacterial pneumonia, the condition either caused or contributed significantly to death. Brucellosis and morbillivirus infections were detected in 7% and 11% of UME dolphins, respectively, and biotoxin levels were low or below the detection limit, indicating that these were not primary causes of the current UME. The rare, life-threatening, and chronic adrenal gland and lung diseases identified in stranded UME dolphins are consistent with exposure to petroleum compounds as seen in other mammals. Exposure of dolphins to elevated petroleum compounds present in coastal GoM waters during and after the DWH oil spill is proposed as a cause of adrenal and lung disease and as a contributor to increased dolphin deaths.

Persistent organic pollutants (POPs) in blubber of common bottlenose dolphins (Tursiops truncatus) along the northern Gulf of Mexico coast, USA

A number of studies were initiated in response to the Deepwater Horizon (DWH) oil spill to understand potential injuries to bottlenose dolphins (Tursiops truncatus) that inhabit the northern Gulf of Mexico (NGoM) estuarine waters. As part of these studies, remote biopsy skin and blubber samples were collected from dolphins at six field sites that received varying degrees of oiling: Barataria Bay (BB), Chandeleur Sound West (CSW), Chandeleur Sound East (CSE), Mississippi Sound South (MSS), Mississippi Sound North (MSN), and St. Joseph Bay (SJ). Blubber samples from 108 male dolphins were analyzed for persistent organic pollutant (POP) concentrations, as high levels of POPs have been previously reported in other southeastern U.S. dolphins and the potential contribution of these compounds to adverse health effects in NGoM dolphins must be considered. Dolphin blubber levels of summed POPs (ΣPOPs) did not differ significantly across sites (F-test, P=0.9119) [μg/g lipid; geometric mean and 95% CI]; CSW [65.9 (51.4–84.6)], SJ [74.1 (53.0–104)], MSN [74.3 (58.7–93.9)], BB [75.3 (56.4–101)], CSE [80.5 (57.8–112)], and MSS [82.5 (65.9–103)]. Overall, POP concentrations were in the lower half of the range compared to previously reported concentrations from other southeastern U.S. sites. Increased dolphin mortalities have been ongoing in the NGoM and have been suggested to be linked with the DWH oil spill. In addition, lung disease, impaired adrenal function, and serum biochemical abnormalities have been reported in dolphins from BB, an area that was heavily oiled. The results of this study suggest that POPs are likely not a primary contributor to the poor health conditions and increased mortality observed in some populations of NGoM dolphins following the DWH oil spill.

Fresh and weathered crude oil effects on potential denitrification rates of coastal marsh soil

On April 20, 2010, the Deepwater Horizon oil platform experienced an explosion which triggered the largest marine oil spill in US history, resulting in the release of ∼795 million L of crude oil into the Gulf of Mexico. Once oil reached the surface, changes in overall chemical composition occurred due to volatilization of the smaller carbon chain compounds as the oil was transported onshore by winds and currents. In this study, the toxic effects of both fresh and weathered crude oil on denitrification rates of coastal marsh soil were determined using soil samples collected from an unimpacted coastal marsh site proximal to areas that were oiled in Barataria Bay, LA. The 1:10 ratio of crude oil:field moist soil fully coated the soil surface mimicking a heavy oiling scenario. Potential denitrification rates at the 1:10 ratio, for weathered crude oil, were 46±18.4% of the control immediately after exposure and 62±8.0% of the control following a two week incubation period, suggesting some adaptation of the denitrifying microbial consortium over time. Denitrification rates of soil exposed to fresh crude oil were 51.5±5.3% of the control after immediate exposure and significantly lower at 10.9±1.1% after a 2week exposure period. Results suggest that fresh crude oil has the potential to more severely impact the important marsh soil process of denitrification following longer term exposure. Future studies should focus on longer-term denitrification as well as changes in the microbial consortia in response to oil exposure.

Spatial and Temporal Variability of Nitrification Potential and Ammonia-Oxidizer Abundances in Louisiana Salt Marshes

We quantified nitrification potential and ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) abundances in 13 salt marshes in three regions across southeast Louisiana (Terrebonne Bay, western and eastern regions of Barataria Bay). Seven marshes were oiled following the 2010 Deepwater Horizon oil spill, and six sites were unoiled marshes. We evaluated spatial variability by sampling transects from marsh edge to interior, as well as temporal variability across regions. Our nitrification potential rates (up to 5,499 nM NO3-N dry g−1 day−1) were much higher than other published rates for salt marshes and we found strong spatial patterns in both nitrification and soil properties. In Terrebonne soils, nitrification potentials peaked in July and increased from marsh edge to interior. Conversely, rates declined with distance from the marsh edge in western Barataria; no spatial patterns were apparent in eastern Barataria marshes. Spatial patterns corresponded to changes in relative elevation, which also influenced patterns of soil properties and ammonia-oxidizer abundances. Nitrification rates were significantly greater in July than September, though no differences were found between regions within either month. Nitrification potential was positively related to ammonia-oxidizer abundance, and significant relationships were only present in the oiled marshes. In Terrebonne marsh soils, nitrification was more strongly related to AOB abundance whereas rates were more strongly related to AOA abundance in Barataria marsh soils. Although we found strong spatial patterns in nitrification, ammonia-oxidizer abundances, and soil properties that appear to, at least in part, be regulated by differences in elevation and hydrology, we found no significant oil effects 2 years post oil-exposure.

Effects of salinity and particle concentration on sediment hydrodynamics and critical bed-shear-stress for erosion of fine grained sediments used in wetland restoration projects

Abstract. Sea-level rise, the increasing number and intensity of storms, oil and groundwater extraction, and coastal land subsidence are putting people and property at risk along Louisiana’s coast, with major implications for human safety and economic health of coastal areas. A major goal towards re-establishing a healthy and sustainable coastal ecosystem has been to rebuild Louisiana’s disappearing wetlands with fine grained sediments that are dredged or diverted from nearby rivers, channels and lakes to build land in open water areas. A thorough geo-hydrodynamic characterization of the deposited sediments is important in the correct design and a more realistic outcome assessment of the long-term performance measures for ongoing coastal restoration projects. This paper evaluates the effects of salinity and solid particle concentration on the re-suspension characteristics of fine-grained dredged sediments obtained from multiple geographic locations along the Gulf coast. The critical bed-shear-stress for erosion has been evaluated as a function of sedimentation time. The sediment hydrodynamic properties obtained from the laboratory testing were used in a numerical coastal sediment distribution model to aid in evaluating sediment diversions from the Mississippi River into Breton Sound and Barataria Bay.

Small-Scale Nekton Density and Growth Patterns Across a Saltmarsh Landscape in Barataria Bay, Louisiana

Nekton on the northern Gulf of Mexico depend on estuarine nursery areas, but patterns of habitat use and the underlying processes that drive these patterns are not fully understood. We examined small-scale (1–50 m) patterns of habitat use in Barataria Bay by collecting nekton samples between 2002 and 2006 with a 1-m2 drop sampler. Habitat-specific densities were estimated for six habitat types at various distances from the shoreline in marsh (Marsh1M = 1 m and Marsh3M = 3 m) and over shallow nonvegetated bottom, SNB (SNB1M = 1 m, SNB5M = 5 m, SNB20M = 20 m, and SNB50M = 50 m). Habitat-specific growth rates also were estimated for brown shrimp Farfantepenaeus aztecus caged in SNB1M, SNB5M, and SNB20M. Nekton density patterns in Barataria Bay appeared to be clearly different from the Galveston Bay model, which predicts nekton distribution patterns relative to the marsh shoreline. Although densities in Barataria Bay were significantly higher in samples near the marsh shoreline (Marsh1M or SNB1M) for brown shrimp, blue crab, and white shrimp, highest mean densities were not always present in marsh edge vegetation. In addition, densities of brown shrimp and white shrimp in Barataria Bay declined much more steeply with distance into the marsh than in the model. Daily growth rates (1.0–1.2 mm TL day−1, 68–89 mg day−1) for brown shrimp were similar among SNB habitat types. Our results suggest that SNB in Barataria Bay may be relatively more important as habitat for fishery species than previously assumed.

Community Structure of Skin Microbiome of Gulf Killifish, Fundulus grandis, Is Driven by Seasonality and Not Exposure to Oiled Sediments in a Louisiana Salt Marsh.

Mucus of fish skin harbors complex bacterial communities that likely contribute to fish homeostasis. When the equilibrium between the host and its external bacterial symbionts is disrupted, bacterial diversity decreases while opportunistic pathogen prevalence increases, making the onset of pathogenic bacterial infection more likely. Because of that relationship, documenting temporal and spatial microbial community changes may be predictive of fish health status. The 2010 Deepwater Horizon oil spill was a potential stressor to the Gulf of Mexico's coastal ecosystem. Ribosomal intergenic spacer analysis (RISA) and pyrosequencing were used to analyze the bacterial communities (microbiome) associated with the skin and mucus of Gulf killifish (Fundulus grandis) that were collected from oiled and non-oiled salt marsh sites in Barataria Bay, LA. Water samples and fin clips were collected to examine microbiome structure. The microbiome of Gulf killifish was significantly different from that of the surrounding water, mainly attributable to shifts in abundances of Cyanobacteria and Proteobacteria. The Gulf killifish's microbiome was dominated by Gammaproteobacteria, specifically members of Pseudomonas. No significant difference was found between microbiomes of fish collected from oiled and non-oiled sites suggesting little impact of oil contamination on fish bacterial assemblages. Conversely, seasonality significantly influenced microbiome structure. Overall, the high similarity observed between the microbiomes of individual fish observed during this study posits that skin and mucus of Gulf killifish have a resilient core microbiome.

Demographic clusters identified within the northern Gulf of Mexico common bottlenose dolphin (Tursiops truncates) unusual mortality event: January 2010-June 2013.

A multi-year unusual mortality event (UME) involving primarily common bottlenose dolphins (Tursiops truncates) was declared in the northern Gulf of Mexico (GoM) with an initial start date of February 2010 and remains ongoing as of August 2014. To examine potential changing characteristics of the UME over time, we compared the number and demographics of dolphin strandings from January 2010 through June 2013 across the entire GoM as well as against baseline (1990-2009) GoM stranding patterns. Years 2010 and 2011 had the highest annual number of stranded dolphins since Louisiana’s record began, and 2011 was one of the years with the highest strandings for both Mississippi and Alabama. Statewide, annual numbers of stranded dolphins were not elevated for GoM coasts of Florida or Texas during the UME period. Demographic, spatial, and temporal clusters identified within this UME included increased strandings in northern coastal Louisiana and Mississippi (March-May 2010); Barataria Bay, Louisiana (August 2010-December 2011); Mississippi and Alabama (2011, including a high prevalence and number of stranded perinates); and multiple GoM states during early 2013. While the causes of the GoM UME have not been determined, the location and magnitude of dolphin strandings during and the year following the 2010 Deepwater Horizon oil spill, including the Barataria Bay cluster from August 2010 to December 2011, overlap in time and space with locations that received heavy and prolonged oiling. There are, however, multiple known causes of previous GoM dolphin UMEs, including brevetoxicosis and dolphin morbillivirus. Additionally, increased dolphin strandings occurred in northern Louisiana and Mississippi before the Deepwater Horizon oil spill. Identification of spatial, temporal, and demographic clusters within the UME suggest that this mortality event may involve different contributing factors varying by location, time, and bottlenose dolphin populations that will be better discerned by incorporating diagnostic information, including histopathology.

Oil detection in the coastal marshes of Louisiana using MESMA applied to band subsets of AVIRIS data

We mapped oil presence in the marshes of Barataria Bay, Louisiana following the Deepwater Horizon oil spill using Airborne Visible InfraRed Imaging Spectrometer (AVIRIS) data. Oil and non-photosynthetic vegetation (NPV) have very similar spectra, differing only in two narrow hydrocarbon absorption regions around 1700 and 2300nm. Confusion between NPV and oil is expressed as an increase in oil fraction error with increasing NPV, as shown by Multiple Endmember Spectral Mixture Analysis (MESMA) applied to synthetic spectra generated with known endmember fractions. Significantly, the magnitude of error varied depending upon the type of NPV in the mixture. To reduce error, we used stable zone unmixing to identify a nine band subset that emphasized the hydrocarbon absorption regions, allowing for more accurate detection of oil presence using MESMA. When this band subset was applied to post-spill AVIRIS data acquired over Barataria Bay on several dates following the 2010 oil spill, accuracies ranged from 87.5% to 93.3%. Oil presence extended 10.5m into the marsh for oiled shorelines, showing a reduced oil fraction with increasing distance from the shoreline.

Oil source-fingerprinting in support of polarimetric radar mapping of Macondo-252 oil in Gulf Coast marshes

Polarimetric synthetic aperture radar (PolSAR) data exhibited dramatic, spatially extensive changes from June 2009 to June 2010 in Barataria Bay, Louisiana. To determine whether these changes were associated with the Deepwater Horizon (DWH) oil spill, twenty-nine sediment samples were collected in 2011 from shoreline and nearshore–interior coastal marsh locations where oil was not observed visually or with optical sensors during the spill. Oil source-fingerprinting and polytopic vector analysis were used to link DWH oil to PolSAR changes. Our results prove that DWH oil extended beyond shorelines and confirm the association between presence of DWH oil and PolSAR change. These results show that the DWH oil spill probably affected much more of the southeastern Louisiana marshland than originally concluded from ground and aerial surveys and verify that PolSAR is a powerful tool for tracking oil intrusion into marshes with high probability even where contamination is not visible from above the canopy.