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As part of the natural resource damage assessment for the Deepwater Horizon oil spill, a mathematical model was used to estimate the total number of bird carcasses deposited on shorelines based on the number of carcasses collected and adjustment factors such as detection probability and carcass persistence. Studies of carcass persistence occurred along sandy beaches and marsh edges in the northern Gulf of Mexico to obtain site-specific inputs for the model. We estimated persistence rates for these habitat types and evaluated the influence on persistence of carcass size, location of the carcass on the beach, dominant vegetation type in the marsh, carcass distance into marsh vegetation, and length of time a carcass was stranded on a shoreline. The length of time stranded had the greatest influence on persistence in both habitat types, with persistence initially relatively low and increasing logarithmically. Carcass size and position were weakly influential on sandy beaches. Carcass size had stronger influences along marsh edges, and marsh habitat type also affected persistence. We found evidence of a positive relationship between distance into the marsh and persistence during the first 24 h after carcass deployment. [ABSTRACT FROM AUTHOR]

Deposition models, such as the Shoreline Deposition Model (SDM) used to quantify nearshore avian injuries resulting from the 2010 Deepwater Horizon (DWH) oil spill, were developed to improve the estimates of nearshore avian mortality resulting from the release of oil into coastal and marine environments. Unlike earlier approaches to injury quantification, such as simple counts of carcasses on the shoreline, a modeling approach allows trustees to evaluate the precision of their estimate (i.e., to develop a confidence interval) and can inform decision-making and the likely utility of additional primary data collection activities through sensitivity analyses. In this paper, we rely on published literature, actual DWH data, and a deposition model simulation to evaluate how different model inputs and assumptions can affect the accuracy and precision of model results. We find that the precision of deposition models is strongly affected by the length of time between subsequent shoreline searches, the underlying magnitude of carcass deposition, carcass persistence probabilities, and carcass detection probabilities. In addition, the accuracy of deposition model results may be affected by natural fluctuations in deposition rates. Given these findings, we recommend that natural resource trustees include an evaluation of future model uncertainty as part of their initial data collection efforts. This will allow them to deploy resources in a way that maximizes the utility of future deposition model results. We also identify several factors that do not need to be assessed immediately following a spill event, thereby potentially freeing resources for more time critical data collection efforts. [ABSTRACT FROM AUTHOR]

In response to the Deepwater Horizon oil spill, federal and state agencies conducted field studies to develop inputs for a shoreline deposition model used to estimate nearshore avian mortality resulting from the spill. A 2011 carcass drift study was designed to generate data on the likelihood that birds that died on the water would deposit along the northern Gulf of Mexico coast (rather than becoming lost at sea). In the case of the Deepwater Horizon oil spill, carcass losses at sea accounted for a significant portion of nearshore avian mortality. We evaluate the data collected during the Deepwater Horizon carcass drift study and compare the results obtained from the use of avian carcasses versus dummy carcasses (dummies) and the differences between those deployed nearshore versus further offshore. We conclude that, although the use of dummies provided valuable confirmation on the drift patterns of dead birds, dummies drifted greater distances, for longer periods of time, and were more likely to be observed beached compared to avian carcasses, with 64.6% of dummies beaching compared to 17.2% of carcasses. In response to future spills, researchers should account for these potential biases when incorporating dummy drift data into estimates of avian carcass loss. Further, none of the avian carcasses and dummies released more than 40 km from the shoreline made it to shore. In the northern Gulf of Mexico, carcasses that die on the waters farther offshore are unlikely to make it to shore to be captured in a deposition model; therefore, it may be appropriate to utilize a separate methodology to estimate offshore mortality. The applicability of these results to other spill events should be evaluated in the context of the specific spill characteristics. [ABSTRACT FROM AUTHOR]

A time series of polycyclic aromatic hydrocarbon (PAH) data was collected for Gulf of Mexico demersal fishes in the years following the Deepwater Horizon oil spill (2012–2017). Tilefish (Lopholatilus chamaeleonticeps) were sampled via demersal longline at repeat stations in the northern Gulf of Mexico in 2012 to 2015 and 2017. Bile samples (n = 256) were analyzed via high‐performance liquid chromatography with fluorescence detection for PAH metabolites as a biomarker of exposure to PAHs. Liver tissues (n = 230) were analyzed for accumulation of PAHs and alkylated homologs via quick, easy, cheap, effective, rugged, and safe (QuEChERS) extractions and gas chromatography–tandem mass spectrometry quantification. Over the 6‐yr time series, exposure to petrogenic PAHs increased by an average of 178%, correlating with an average 22% decline in Fulton's condition factor. The decline in Fulton's condition factor was positively correlated with a 53% decline in percentage of liver lipid. There was no accumulation of PAHs in liver tissue over time. Together, these results suggest that increasing and chronic PAH exposure and metabolism may be taxing the energy budgets of tilefish, particularly adult females, with potentially negative impacts on fitness. Environ Toxicol Chem 2019;38:2659–2671. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The Gulf of Mexico Research Initiative (GoMRI) was established in 2010 with $500 million in funding provided by British Petroleum over a 10‐year period to support research on the impacts of the Deepwater Horizon oil spill and recovery. Contributions of the GoMRI program to date focused on human health are presented in more than 32 peer‐reviewed papers published between 2011 and May 2019. Primary findings from review of these papers are (i) the large quantity of dispersants used in the oil cleanup have been associated with human health concerns, including through obesogenicity, toxicity, and illnesses from aerosolization of the agents; (ii) oil contamination has been associated with potential for increases in harmful algal blooms and numbers of pathogenic Vibrio bacteria in oil‐impacted waters; and (iii) members of Gulf communities who are heavily reliant upon natural resources for their livelihoods were found to be vulnerable to high levels of life disruptions and institutional distrust. Positive correlations include a finding that a high level of community attachment was beneficial for recovery. Actions taken to improve disaster response and reduce stress‐associated health effects could lessen negative impacts of similar disasters in the future. Furthermore, GoMRI has supported annual conferences beginning in 2013 at which informative human health‐related presentations have been made. Based on this review, it is recommended that the Oil Pollution Act of 1990 be updated to include enhanced funding for oil spill impacts to human health. Key Points: Nearly 3% of >1,200 Gulf of Mexico Research Initiative publications were directly related to human health, a higher proportion than previous oil spill researchDispersants contained possible obesogens and decreased aerosolized volatile organic compound exposure but increased particulate matter concentrationsThose who rely on natural resources are more vulnerable to oil spills and cleanup methods that may increase exposure to harmful chemicals, algae, and bacteria [ABSTRACT FROM AUTHOR]

In the wake of the Deepwater Horizon disaster, much has been learned about the biological, ecological, physical, and chemical conditions of the Gulf of Mexico. In parallel, the research community has also gained insight about the social and organizational structures and processes necessary for oil spill response and subsequent marine and coastal restoration. However, even with these lessons from both the Deepwater Horizon and previous spills, including 1989's Exxon Valdez and the Ixtoc 1 in 1979, our understanding of how to avoid future crises has not advanced at the same pace as offshore oil and gas development. We argue that this progress deficit indicates a continued devaluing of marine and coastal resources. We believe that we must, instead, advance a proactive conservation ethic based on the precautionary principle and an appropriately placed burden of proof—strategies that will help reduce our reliance on costly restoration and protect marine and coastal ecosystems. [ABSTRACT FROM AUTHOR]

Opaque fluid flow estimation is a challenging problem due to the complex nature of this flow type. Deepwater Horizon oil spill is one of the real examples of opaque fluid flow. Due to the complicated spill flow and the lack of dedicated flow measurement technique its flow rate was estimated with high uncertainty. In this paper, a simulation of jet flow is conducted experimentally and numerically. This is in order to analyze the difference between them. First, a turbulent buoyant jet was experimentally simulated considering various ranges of nozzle flow rates including laminar and turbulent flow. A video camera was used to capture the jet flow. Then, Fast Fourier Transform (FFT) based method was developed to estimate velocity field from video sequence. The outcomes of experimental results were compared to the outcomes of numerical simulation. As a result, the FFT-based method was estimated the nozzle flow rates with a relative error of 18.2% when it was compared to the measured experimental values. Despite this poor accuracy, a good agreement between experimental and numerical simulation outcomes was found in term of overall velocity field, centerline velocity, axial velocity as well as the distribution of radial velocity. [ABSTRACT FROM AUTHOR]

Dispersant application is a primary emergency oil spill response strategy and yet the efficacy and unintended consequences of this approach in marine ecosystems remain controversial. To address these uncertainties, ex situ incubations were conducted to quantify the impact of dispersant on petroleum hydrocarbon (PHC) biodegradation rates and microbial community structure at as close as realistically possible to approximated in situ conditions [2 ppm v/v oil with or without dispersant, at a dispersant to oil ratio (DOR) of 1:15] in surface seawater. Biodegradation rates were not substantially affected by dispersant application at low mixing conditions, while under completely dispersed conditions, biodegradation was substantially enhanced, decreasing the overall half-life of total PHC compounds from 15.4 to 8.8 days. While microbial respiration and growth were not substantially altered by dispersant treatment, RNA analysis revealed that dispersant application resulted in pronounced changes to the composition of metabolically active microbial communities, and the abundance of nitrogen-fixing prokaryotes, as determined by qPCR of nitrogenase (nifH) genes, showed a large increase. While the Gammaproteobacteria were enriched in all treatments, the Betaproteobacteria and different families of Alphaproteobacteria predominated in the oil and dispersant treatment, respectively. Results show that mixing conditions regulate the efficacy of dispersant application in an oil slick, and the quantitative increase in the nitrogen-fixing microbial community indicates a selection pressure for nitrogen fixation in response to a readily biodegradable, nitrogen-poor substrate. [ABSTRACT FROM AUTHOR]

Dispersants are used to reduce the impact of oil spills in marine environment. Experiments were conducted with natural materials which were contaminated by direct application of fresh Louisiana crude oil. The natural materials evaluated included sea sand (South Beach in Miami, Florida), red mangrove leaves (Rhizophora mangle), and sea shells (Donax variabili). Salt water at two different salinities (17 and 34 ppt) was used with two types of Corexit dispersant solutions (9500A and 9527A) in concentrations ranging from 100 to 3500 mg/L. Washing of the contaminated samples was conducted by a three-step mixing procedure (salt water only, then with the addition of the dispersant solution to the salt water, and salt water) to simulate oil-saltwater-dispersant interactions. In general, increasing dispersant concentration increased the percentage of oil dispersed into the aqueous phase up to dispersant solutions containing 400 mg/L for Corexit 9500A and 300 mg/L Corexit 9527A. Increasing the dispersant concentration above these levels also decreased the dispersion of oil from the surfaces. At very high concentrations of dispersant solutions (above 1500 mg/L), the percentage of oil dispersed into the solution from the contaminated surfaces was about one half what was observed at 400 mg/L with Corexit 9500A and 300 mg/L Corexit 9527A. Although dispersants were most effective for removing the fresh Louisiana crude oil from sand particles and dispersing into the solution due to large surface area of the particles per unit weight; the residual oil remaining on the sand particles was relatively high in comparison to mangrove leaves and sea shells due to clustering of sand particle with oil. There was some oil penetration into the porous structure of the sea shells (at the microscopic level) which could not be removed. Image 1 • A three step washing process was used to clean crude oil contaminated natural materials. • Two commonly used oil spill dispersants (Corexit 9500A and Corexit 9527A) were evaluated. • Contaminated sea sand, shells (Donax variabili), and r ed mangrove (Rhizophora mangle) leaves were evaluated. • Increasing dispersant concentration up to 400 mg/L increased the oil dispersed into the aqueous phase. • Higher residual oil remained on sand surfaces due to clustering of particles with oil. [ABSTRACT FROM AUTHOR]

We used high-resolution fisheries-dependent data and a quantitative modeling approach to examine resilience of a commercial reef fish fleet after the Deepwater Horizon oil spill (DWH) emergency closures in 2010. Our results indicate that the fleet was largely resilient to the closures, although there were spatially-varying differences in attrition, and concomitant management changes and emergency payouts that likely influenced resilience. Five percent of previously active vessels exited the fleet after DWH (compared to the background annual attrition rate of ˜20%). The predicted probability of exiting after DWH was lower for vessels with a pre-closure history of high catch-per-unit-effort, low snapper revenue variability, or low grouper revenue. There was ˜80% overlap in pre- to post-DWH effort distribution, although vessels that exited concentrated effort in the north-central and eastern Gulf of Mexico. The Vessels of Opportunity program and other emergency compensation likely ameliorated some of the negative economic impacts from DWH, allowing more vessels to remain in the fleet than may have otherwise. Implementation of gear restrictions and individual fishing quotas leading up to DWH may have also 'primed' the fleet for resilience by removing marginal fishers. This work is novel in its use of high-resolution spatial data, coupled with trip logbooks, to construct quantitative models identifying drivers of fisher resilience after significant and sudden perturbations to fishery resources in the Gulf of Mexico. This work also highlights the need to better understand fisher response to disturbance for long-term fishery sustainability and management. [ABSTRACT FROM AUTHOR]

Welfare measures from travel cost models net out variable costs such as travel expenses specific to each trip. Costs that are fixed in the short run, such as expenses for equipment that is used over multiple trips, are typically ignored and implicitly netted out. The resulting net value of recreation trips, or consumer surplus, is appropriate for long-run analysis when consumers can fully adjust their expenditures. However, in cases where some costs are difficult to adjust in the short run, such as when boat owners do not sell their boats in response to the transient effects of an oil spill, traditional consumer surplus measures underestimate the total welfare change. We explain this underestimation and show how to correct for it by adjusting traditional consumer surplus estimates upward. We illustrate our procedure using a model of recreational boating developed to assess damages from the Deepwater Horizon oil spill. In that case, accounting for boating fixed costs resulted in a 50% increase in estimated value relative to estimates of consumer surplus alone. [ABSTRACT FROM AUTHOR]

Although photochemical oxidation is an environmental process that drives organic carbon (OC) cycling, its quantitative detection remains analytically challenging. Here, we use samples from the Deepwater Horizon oil spill to test the hypothesis that the stable oxygen isotope composition of oil (δ18OOil) is a sensitive marker for photochemical oxidation. In less than one‐week, δ18OOil increased from −0.6 to 7.2‰, a shift representing ~25% of the δ18OOC dynamic range observed in nature. By accounting for different oxygen sources (H2O or O2) and kinetic isotopic fractionation of photochemically incorporated O2, which was −9‰ for a wide range of OC sources, a mass balance was established for the surface oil's elemental oxygen content and δ18O. This δ18O‐based approach provides novel insights into the sources and pathways of hydrocarbon photo‐oxidation, thereby improving our understanding of the fate and transport of petroleum hydrocarbons in sunlit waters, and our capacity to respond effectively to future spills. Plain Language Summary: Sunlight alters the physical and chemical properties of petroleum hydrocarbons released into aquatic ecosystems. These alterations impact the performance of chemical tools used in response to oil spills, and thus there is substantial interest in improving approaches to track these alterations and our understanding of the driving mechanisms. In this study, we developed a stable oxygen isotope‐based approach to track photochemical oxidation of oil and validated it using samples from the 2010 Deepwater Horizon oil spill. Our isotope‐based approach revealed two key insights into the photochemical oxidation mechanism. First, the major source of oxygen added to the oil by sunlight appears to be molecular oxygen rather than water. Second, molecular oxygen kinetic isotope fractionation during photochemical oxidation was remarkably similar for a wide range of organic carbon types, such as crude oil and dissolved organic carbon, raising the possibility of a common step in the oxidation mechanism. This new stable oxygen isotope‐based approach will improve our capacity to respond effectively to future oil spills, and can be applied to track the cycling of a broad range of organic carbon sources. Key Points: Stable oxygen isotopes sensitively track the photochemical oxidation of Deepwater Horizon surface oilMolecular oxygen appears to be the major source of oxygen photochemically added to hydrocarbonsThe kinetic isotope effect of photochemical oxidation is consistently −9‰ for oil and for a variety of organic carbon sources [ABSTRACT FROM AUTHOR]

Abstract Acute exposure to crude oil and polycyclic aromatic hydrocarbons (PAH) can severely impair cardiorespiratory function and swim performance of larval, juvenile and adult fish. Interestingly, recent work has documented an oil induced decoupling of swim performance (U crit) and maximum metabolic rate (MMR) whereby oil causes a decline in U crit without a parallel reduction in MMR. We hypothesize that this uncoupling is due to impaired mitochondrial function in swimming muscles that results in increased proton leak, and thus less ATP generated per unit oxygen. Using high resolution mitochondrial respirometry, we assessed 11 metrics of mitochondrial performance in red and cardiac muscle from permeabilized fibers isolated from red drum following control or 24 h crude oil (high energy water accommodated fractions) exposure. Two experimental series were performed, a Deepwater Horizon relevant low dose (29.6 ± 7.4 μg L−1 ∑PAH 50) and a proof-of-concept high dose (64.5 ± 8.9 μg L−1 ∑PAH 50). No effects were observed on any mitochondrial parameter in either tissue at the low oil dose; however, high dose exposure provided evidence of impairment in the OXPHOS respiratory control ratio and OXPHOS spare capacity in red muscle following oil exposure, as well as a shift from Complex I to Complex II during OXPHOS respiration. No effects of the high dose oil treatment were observed in cardiac muscle. As such, mitochondrial dysfunction is unlikely to be the underlying mechanism for decoupling of U crit and MMR following acute oil exposure in red drum. Furthermore, mitochondrial dysfunction does not appear to be a relevant toxicological impairment in juvenile red drum with respect to the Deepwater Horizon oil spill, although impairments may be observed under higher dose exposure scenarios. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Drilling incidents have emphasized that offshore drillers require a high level of cognitive skills, including situation awareness and decision making, to maintain safe and efficient well control. Although a number of tools for supporting operators' cognition are available in other high-risk industries, there is no specific tool for drilling. We developed a prototype monitoring task simulating drilling scenarios, Drillers' Situation Awareness Task, with drilling experts and piloted with 14 drilling personnel. Preliminary results suggest that it is viable as a tool for examining drillers' cognition and has the potential for training and formatively assessing cognitive skills in drilling. [ABSTRACT FROM AUTHOR]

Abstract Background On April 20, 2010, the Deepwater Horizon oil rig exploded, spilling over 4.9 million barrels of oil in the Gulf of Mexico over an 87-day period and developing into a long-term environmental disaster that affected people living in Gulf Coast states. Engagement of community members in recovery efforts is important for mitigating adverse effects of disasters and accelerating the rebuilding process for impacted communities; however, few studies have explored factors that determine participation in oil spill cleanups. Methods We analyzed data from the Gulf States Population Survey (GSPS) to study the determinants of participating in the Deepwater Horizon Oil Spill cleanup. The GSPS was a random-digit dialing survey conducted on 38,361 adults in counties and parishes in Alabama, Florida, Louisiana, and Mississippi impacted by the oil spill. Using survey estimation to account for the complex survey design, we estimated the probability of cleanup participation and used logistic regression to examine the association between sociodemographic factors and cleanup participation. Results Approximately 4.7% of residents in affected Gulf communities participated in the cleanup. Most participants were young, men, non-Hispanic white, and employed. Living in an affected coastal county was associated with higher odds of participation (unadjusted odds ratio [OR]: 1.69; 95% confidence interval [CI]: 1.28–2.24), as was having excellent or very good physical health (OR: 2.05; 95% CI: 1.11–3.81). Older persons were less likely to participate in the cleanup (OR for 65+ age group vs. 18–24 age group: 0.14; 95% CI: 0.05–0.36). Conclusions Understanding the demographics of cleanup participants may help inform civilian recruitment for future oil spill responses. Highlights • An estimated 4.7% of residents in impacted areas participated in the cleanup of the Deepwater Horizon oil spill. • Most cleanup participants were young white men, highlighting the need to target members of underrepresented groups. • Approximately seven out of ten participants were volunteers, with most persons assisting with less dangerous cleanup tasks. • Having optimal physical health and living in an affected coastal county were associated with cleanup participation. [ABSTRACT FROM AUTHOR]

This article provides a description of the rationale and processes adopted by the Gulf Coast Health Alliance: Health Risks related to the Macondo Spill consortium to evaluate and communicate the risk of exposure to polycyclic aromatic hydrocarbons (PAHs) in seafood over several years following the Deepwater Horizon disaster and subsequent oil spill. We examined gaps in knowledge associated with PAH toxicity following exposure to petrogenic (oil-derived) PAHs by studying the metabolic fate of PAHs and their potential toxicity using sophisticated analytical methods. Using the data generated, we developed a risk communication strategy designed to meet the needs of the stakeholder communities including a consumption guideline calculator, a web-based tool to reconcile seafood consumption with risk of adverse health effects. [ABSTRACT FROM AUTHOR]

This introduction to the special issue continues an examination of the Gulf Coast Health Alliance: Health Risks Related to the Macondo Spill (GC-HARMS) project that began in New Solutions 28:3. GC-HARMS was part of a National Institute of Environmental Health Sciences-funded Gulf-wide consortium that created regional community-university research partnerships addressing health impacts from the oil spill exposures. Findings from this program enhanced regional preparedness and reinforced existing disaster-response networks. This special issue of New Solutions includes an article exploring the outcomes and implications of using a community-based participatory research—citizen science approach in implementing the project's exposure assessment/population health study and another article that describes analytic processes used to characterize toxicity of petrogenic Polycyclic Aromatic Hydrocarbons which provided data used to develop the project's risk message. Finally, this issue includes three Movement Voices interviews from individuals and nonprofits that served as GC-HARMS community hubs during the project. [ABSTRACT FROM AUTHOR]

Abstract The Deepwater Horizon (DWH) oil spill was the biggest in US history and released 3.19 million barrels of light crude oil into the Gulf of Mexico. In this study, we compared the toxicity of water accommodated fractions (WAFs) of naturally weathered crude oils, source oil, and source oil with dispersant mixtures and their effects on developing sheepshead minnow and zebrafish. Although a freshwater fish, zebrafish has been used as a model for marine oil spills owing to the molecular and genetic tools available and their amenability to lab care. Our study not only aimed to determine the effect of crude oil on early life stages of these two fish species, but also aimed to determine whether dissolved crude oil constituents were similar in fresh and saltwater, and if freshwater fish might be a suitable model to study marine spills. Weathering and dispersant had similar effects on WAF composition in both fresh and saltwater, except that the saltwater source oil + dispersant WAF had markedly higher PAH levels than the freshwater equivalent. WAF exposure differentially affected survival, as the LC50 values in %WAF for the zebrafish and sheepshead minnow exposures were 44.9% WAF (95% confidence interval (C.I.) 42.1–47.9) and 16.8% WAF (95% C.I. 13.7–20.5); respectively. Exposure increased heart rate of zebrafish embryos, whereas in sheepshead, source oil exposure had the opposite effect. WAF exposure altered mRNA expression of biotransformation makers, vitellogenin and neurodevelopment genes in both species. Muscle deformations were only found in oil-exposed zebrafish. This is one of the most comprehensive studies to date on crude oil toxicity, and highlights the species-specific differences in cardiotoxicity, estrogenic effects, biotransformation enzyme induction and potential neurotoxicity of crude oil exposure. Graphical abstract Unlabelled Image Highlights • The addition of dispersant increased the toxicity of source oil WAFs. • Dispersant + source oil WAF in saltwater had higher PAH levels than the freshwater equivalent. • Free-swimming vs chorion bound exposure time may play a role in determining the toxicity of early life-stage exposures • There are limitations to using freshwater species, like zebrafish, to model marine oil spills. • Interspecies molecular and physiological responses to crude oil can differ significantly. [ABSTRACT FROM AUTHOR]

The Deepwater Horizon oil well blowout discharged an unprecedented amount of methane into the water column of the northern Gulf of Mexico between April and July 2010. The methanotrophic community bloomed in response to the sustained methane release, resulting in the highest methane oxidation rates measured in the water column of an open ocean environment to date. To assess the long-term impact and recovery of the northern Gulf of Mexico methanotrophic community, we tracked methane dynamics for five years post-blowout. We determined methane concentration and methane oxidation rates at 31 different sites, resulting in ~900 discrete water column samples across the northern Gulf ecosystem, the largest compilation of methane oxidation rate measurements in an offshore ocean environment. Though methane concentrations approached pre-blowout concentrations within one year, methane oxidation rates exhibited a more gradual trend of decreasing activity. These results suggest that Gulf-wide circulation patterns dispersed and redistributed methanotrophic biomass that bloomed and accumulated in the wake of the Deepwater Horizon blowout, and that this biomass was able to perpetuate elevated methanotrophic activity for multiple years after the blowout at levels above anticipated background rates. This dataset provides a rare view of the response of an ocean ecosystem to a large pulse of methane and reveals unanticipated dynamics of microbial methanotrophy as a result of such human-induced methane releases.

Blue crabs, Callinectes sapidus Rathbun, 1896, are ubiquitous along the Atlantic and Gulf coasts of the USA. These organisms play an integral role in the ecosystems of the Gulf of Mexico (GOM), where not only are they a keystone species, but are also socioeconomically important. The survival of embryonated eggs is necessary to ensure adequate recruitment into the next generation. Because the 2010 Deepwater Horizon oil spill (DWH) occurred during the peak of the blue crab spawning season, the incident likely impacted blue crab embryos. In order to assess the effect of oil on embryonic growth and development, we collected embryonated eggs from seven different female blue crabs from the GOM throughout the spawning season and exposed them to an oil concentration of 500 ppb (the approximate concentration of oil at the surface water near the site of the Deepwater Horizon oil rig). Exposure to oil at this concentration caused a significantly larger proportion of prezoeae vs. zoeae to hatch from embryonated eggs in experiments lasting longer than 4 days. Exposure to oil did not significantly affect overall survival or development rate. The prezoeal stage is a little-studied stage of blue crab development. Though it may or may not be a normal stage of development, this stage has been found to occur in suboptimal conditions and has lower survival than zoeal stages. The larger proportion of prezoeae following prolonged exposure to oil thus indicates that crude oil at concentrations likely to be experienced by crabs after the DWH spill negatively impacted the development of blue crab embryos. In addition to providing insight into the effects of the DWH, this study sheds light on embryonic development in blue crabs, a critical, but poorly investigated phase of this important species’ life cycle.

During the Deepwater Horizon (DWH) oil spill, massive quantities of oil were deposited on the seafloor via a large-scale marine oil-snow sedimentation and flocculent accumulation (MOSSFA) event. The role of chemical dispersants (e.g., Corexit) applied during the DWH oil spill clean-up in helping or hindering the formation of this MOSSFA event are not well-understood. Here, we present the first experiment related to the DWH oil spill to specifically investigate the relationship between microbial community structure, oil and Corexit®, and marine oil-snow in coastal surface waters. We observed the formation of micron-scale aggregates of microbial cells around droplets of oil and dispersant and found that their rate of formation was directly related to the concentration of oil within the water column. These micro-aggregates are potentially important precursors to the formation of larger marine oil-snow particles. Therefore, our observation that Corexit® significantly enhanced their formation suggests dispersant application may play a role in the development of MOSSFA events. We also observed that microbial communities in marine surface waters respond to oil and oil plus Corexit® differently and much more rapidly than previously measured, with major shifts in community composition occurring within only a few hours of experiment initiation. In the oil-amended treatments without Corexit®, this manifested as an increase in community diversity due to the outgrowth of several putative aliphatic- and aromatic-hydrocarbon degrading genera, including phytoplankton-associated taxa. In contrast, microbial community diversity was reduced in mesocosms containing chemically dispersed oil. Importantly, different consortia of hydrocarbon degrading bacteria responded to oil and chemically dispersed oil, indicating that functional redundancy in the pre-spill community likely results in hydrocarbon consumption in both undispersed and dispersed oils, but by different bacterial taxa. Taken together, these data improve our understanding of how dispersants influence the degradation and transport of oil in marine surface waters following an oil spill and provide valuable insight into the early response of complex microbial communities to oil exposure.

Abstract Climate change is causing shifts in the distribution and abundance of many species. Because species vary in the rate and degree of these shifts, novel transition zones have developed where new combinations of species overlap. If climate‐mediated range shifts result in greater diversity, transition communities could have enhanced resistance and/or resilience, particularly if the resident and colonizing species differ in their response to environmental change. The range expansion of the tropical black mangrove, Avicennia germinans, into salt marshes dominated by the temperate cordgrass, Spartina alterniflora, provides an opportunity to examine the responses of climate‐mediated transition zones to disturbance. We conducted a yearlong mesocosm experiment testing the effects of plant species identity and composition (A. germinans, S. alterniflora), as well as plant genotypic diversity (S. alterniflora only), on the response of coastal wetlands to oiling disturbance. Oil negatively impacted S. alterniflora and A. germinans both above‐ and belowground, though the timing of these effects varied, with S. alterniflora showing more immediate declines than A. germinans. As hypothesized, the magnitude of the oil effect was reduced in the mixed plant species treatment compared to the single species treatment for A. germinans survival (12% vs. 21% reduction) and belowground biomass (19% vs. 71% reduction). In addition, when exposed to oil, A. germinans crown area and volume were greater in the mixed species treatment compared to the single species treatment at the end of the experiment. However, we did not detect any benefit of mixed species communities or S. alterniflora genotypic diversity for the S. alterniflora response to oil. Our results suggest that transition habitats in the northern Gulf of Mexico where A. germinans and S. alterniflora co‐occur will be negatively impacted by future oiling events, but that they are no more susceptible, and perhaps slightly less so, than habitats dominated by either individual species.

The Deepwater Horizon oil spill was one of the largest and deepest oil spills recorded. The wellhead was located at approximately 1500 m below the sea where low temperature and high pressure are key environmental characteristics. Using cells collected 4 months following the Deepwater Horizon oil spill at the Gulf of Mexico, we set up Macondo crude oil enrichments at wellhead temperature and different pressures to determine the effect of increasing depth/pressure to the in situ microbial community and their ability to degrade oil. We observed oil degradation under all pressure conditions tested [0.1, 15, and 30 megapascals (MPa)], although oil degradation profiles, cell numbers, and hydrocarbon degradation gene abundances indicated greatest activity at atmospheric pressure. Under all incubations the growth of psychrophilic bacteria was promoted. Bacteria closely related to Oleispira antarctica RB-8 dominated the communities at all pressures. At 30 MPa we observed a shift toward Photobacterium, a genus that includes piezophiles. Alphaproteobacterial members of the Sulfitobacter, previously associated with oil-degradation, were also highly abundant at 0.1 MPa. Our results suggest that pressure acts synergistically with low temperature to slow microbial growth and thus oil degradation in deep-sea environments.

Seafloor sediment resuspension events of different scales and magnitudes and the resulting deep (>1,000 m) benthic nepheloid layers were investigated in the northern Gulf of Mexico during Fall 2012 to Summer 2013. Time-series data of size-specific 'in-situ' settling speeds of marine snow in the benthic nepheloid layer (moored flux cameras), particle size distributions (profiling camera), currents (various current meters) and stacked time-series flux data (sediment traps) were combined to recognize resuspension events ranging from small-scale local, to small-scale far-field to hurricane-scale. One small-scale local resuspension event caused by inertial currents was identified based on local high current speeds (>10 cm s–1) and trap data. Low POC content combined with high lithogenic silica flux at 30 m above bottom (mab) compared to the flux at 120 mab, suggested local resuspension reaching 30 mab, but not 120 mab. Another similar event was detected by the changes in particle size distribution and settling speeds of particles in the benthic nepheloid layer. Flux data indicated two other small-scale events, which occurred at some distance, rather than locally. Inertia-driven resuspension of material in shallower areas surrounding the traps presumably transported this material downslope leaving a resuspension signal at 120 mab, but not at 30 mab. The passage of hurricane Isaac left a larger scale resuspension event that lasted a few days and was recorded in both traps. Although hurricanes cause large-scale events readily observable in sediment trap samples, resuspension events small in temporal and spatial scale are not easily recognizable in trapped material as they tend to provide less material and become part of the background signal in the long-term averaged trap samples. We suggest that these small-scale resuspension events, mostly unnoticed in conventional time-series sampling, play an important role in the redistribution and ultimate fate of sediment distribution on the seafloor.

Response management and damage assessment during and after environmental disasters such as the Deepwater Horizon (DWH) oil spill require an ecological baseline and a solid understanding of the main drivers of the ecosystem. During the DWH event, a large fraction of the spilled oil was transported to depth via sinking marine snow, a routing of spilled oil unexpected to emergency response planners. Because baseline knowledge of particle export in the Northern Gulf of Mexico and how it varies spatially and temporally was limited, we conducted a detailed assessment of the potential drivers of deep (~1400 m depth) particle fluxes during 2012–2016 using sediment traps at three contrasting sites in the Northern Gulf of Mexico: near the DWH site, at an active natural oil seep site, and at a site considered typical for background conditions. The DWH site, located ~70 km from the Mississippi River Delta, showed flux patterns that were strongly linked to the Mississippi nitrogen discharge and an annual subsequent surface bloom. Fluxes carried clear signals of combustion products, which likely originated from pyrogenic sources that were transported offshore via the Mississippi plume. The seep and reference sites were more strongly influenced by the open Gulf of Mexico, did not show a clear seasonal flux pattern, and their overall sedimentation rates were lower than those at the DWH site. At the seep site, based on polycyclic aromatic hydrocarbon data, we observed indications of three different pathways for “natural” oiled-snow sedimentation: scavenging by sinking particles at depth, weathering at the surface before incorporation into sinking particles, and entry into the food web and subsequent sinking in form of detritus. Overall, sedimentation rates at the three sites were markedly different in quality and quantity owing to varying degrees of riverine and oceanic influences, including natural seepage and contamination by combustion products.