Interactions between oil-spill pollutants and natural stressors can compound ecotoxicological effects

Polycyclic Aromatic Hydrocarbons (PAHs) in aquatic ecosystem exposed to the 2020 Baghjan oil spill in upper Assam, India: Short-term toxicity and ecological risk assessment

This study focuses on the short-term contamination and associated risks arising from the release of Polycyclic Aromatic Hydrocarbons (PAHs) due to the 2020 Baghjan oil blowout in upper Assam, India. Shortly after the Baghjan oil blowout, samples were collected from water, sediment, and fish species and examined for PAHs contents. The results of the analysis revealed ΣPAHs concentrations ranged between 0.21-691.31 μg L-1 (water); 37.6-395.8 μg Kg-1 (sediment); 104.3-7829.6 μg Kg-1 (fish). The prevalence of 3-4 ring low molecular weight PAHs compounds in water (87.17%), sediment (100%), and fish samples (93.17%) validate the petrogenic source of origin (oil spill). The geographic vicinity of the oil blowout is rich in wildlife; thus, leading to a significant mass mortality of several eco-sensitive species like fish, plants, microbes, reptiles, amphibians, birds and mammals including the Gangetic River dolphin. The initial ecological risk assessment suggested moderate to high-risk values (RQ >1) of majority PAHs concerning fish, daphnia, and algae species. This study highlights the need for recognizing the potential for short-term exposure to local species. To safeguard local ecosystems from potential future environmental disasters, it is imperative for the government to adopt a precautionary strategy.

Remote sensing reveals unprecedented sublethal impacts of a 40-year-old oil spill on mangroves

Oil spills cause long-lasting mangrove loss, threatening their conservation and ecosystem services worldwide. Oil spills impact mangrove forests at various spatial and temporal scales. Yet, their long-term sublethal effects on trees remain poorly documented. Here, we explore these effects based on one of the largest oil spills ever recorded, the Baixada Santista pipeline leak, which hit the mangroves of the Brazilian southeastern coast in 1983. Historical, Landsat-derived normalized difference vegetation index (NDVI) maps over the spilled mangrove reveal a large dieback of trees within a year following the oil spill, followed by a heigh-year recolonization period and a stabilization of the canopy cover, however 20-30% lower than initially observed. We explain this permanent loss by an unexpected persistence of oil pollution in the sediments based on visual and geochemical evidence. Using field spectroscopy and cutting-edge drone hyperspectral imaging, we demonstrate how the continuous exposure of mangrove trees to high levels of pollution affects their health and productivity in the long term, by imposing permanent stressful conditions. Our study also reveals that tree species differ in their sensitivity to oil, giving the most tolerant ones a competitive advantage to recolonize spilled mangroves. By leveraging drone laser scanning, we estimate the loss of forest biomass caused by the oil spill to 9.8-91.2 t ha^-1, corresponding to 4.3-40.1 t C ha^-1. Based on our findings, we encourage environmental agencies and lawmakers to consider the sublethal effects of oil spills on mangroves in the environmental cost of these accidents. We also encourage petroleum companies to use drone remote sensing in monitoring routines and oil spill response planning to improve mangrove preservation and impact assessment.

Effects of the water-soluble fraction of diesel oil on the sera biochemical indicators, histological changes, and immune responses of black rockfish Sebastes schlegelii

In order to understand the physiological and immune responses of Sebastes schlegelii to the water-soluble fraction of diesel oil (WSD), S. schlegelii were used as the experimental objects to study the effect of WSD on the sera biochemical indicators, histological changes, and immune responses. Significant differences in sera biochemical indicators were observed in S. schlegelii after WSD exposure. The alkaline phosphatase (ALP), glucose (GLU), and globulin (GLB) were reduced by 3.51-fold, 3.12- fold, and 1.58-fold, respectively; however, K⁺ was increased by 3.55-fold. The results of HE staining showed that interstitial congestion was observed in the liver; the secondary lamellae deformity and hyperplasia, epithelial lifting, the primary lamellae hyperplasia, and aneurism were observed in the gill. Epidermis thickness increased, and epidermal hyperplasia in the skin was shown. The length of the secondary lamellae shortened significantly after WSD exposure. The results of AB-PAS staining showed that three different types of mucous cells were observed in the gill, and a significant increase in the number of all three types of mucous cells was observed after WSD exposure (P < 0.05). In addition, the results of the relative mRNA expressions in the liver of eleven immune-related genes showed that the relative expression levels of IL-1β, IL-8, TNF receptor, BAFF, C1s, C1r, and MyD88 in the WSD group were substantially higher than those in the LPS group (P < 0.05), and the relative expression of caspase 10 was significantly lower than that in the LPS group (P < 0.05). At the same time, no significant differences were observed in the relative expression levels of IL-1, TNFα, and C1inh between the two groups (P > 0.05). This study was expected to provide essential data for health assessments of S. schlegelii and establish the foundation for the immune-related researches of S. schlegelii after WSD exposure.

Early developmental toxicity of Atlantic salmon exposed to conventional and unconventional oils

Atlantic salmon is an important species for Canadian culture and economy and its importance extends beyond Canada to Scandinavia and Western Europe. However, it is a vulnerable species facing decline due to habitat contamination and destruction. Existing and new Canadian pipeline projects pose a threat to salmonid habitat. The effects of diluted bitumen (dilbit), the main oil circulating in pipelines, are less studied than those of conventional oils, especially during the critical early embryonic developmental stage occurring in freshwater ecosystems. Therefore, this study aimed to compare the effects of water-accommodated fractions (WAF) of the Clearwater McMurray dilbit and the Lloydminster Heavy conventional oil on Atlantic salmon embryos exposed either from fertilization or from eyed stage. The dilbit contained the highest concentrations of low molecular weight (LMW) compounds (including BTEX and C₆-C₁₀), while the conventional oil contained the highest concentrations of PAHs. The Clearwater dilbit caused a higher percentage of mortality and malformations than the conventional oil at similar WAF concentrations. In addition, the embryos exposed from fertilization suffered a higher mortality rate, more developmental delays, and malformations than embryos exposed from the eyed stage, suggesting that early development is the most sensitive developmental stage to oil exposure. Gene expression and enzymatic activity of the detoxification phase I and II enzymes (CYP1A and GST) were measured. Data showed increases in both cyp1a expression and GST activity with increasing WAF concentrations, while gst expression was not affected by the exposures. Also, gene expression of proteins involved in the biotransformation of vitamin A and DNA damage repair were modified by the oil exposures. Overall, this study indicates that Atlantic salmon is mostly affected by oil exposure at the beginning of its development, during which embryos accumulate deformities that may impact their survival at later life stages.

Responses to simultaneous anthropogenic and biological stressors were mixed in an experimental saltmarsh ecosystem

Coastal ecosystems are essential for absorbing and bouncing back from the impacts of climate change, yet accelerating climate change is causing anthropogenically-derived stressors in these ecosystems to grow. The effects of stressors are more difficult to foresee when they act simultaneously, however, predicting these effects is critical for understanding ecological change. Spartina alterniflora (Spartina), a foundational saltmarsh plant key to coastal resilience, is subject to biological stress such as herbivory, as well as anthropogenic stress such as chemical pollution. Using saltmarsh mesocosms as a model system in a fully factorial experiment, we tested whether the effects of herbivory and two chemicals (oil and dispersant) were mediated or magnified in combination. Spartina responded to stressors asynchronously; ecophysiology responded negatively to oil and herbivores in the first 2-3 weeks of the experiment, whereas biomass responded negatively to oil and herbivores cumulatively throughout the experiment. We generally found mixed multi-stressor effects, with slightly more antagonistic effects compared to either synergistic or additive effects, despite significant reductions in Spartina biomass and growth from both chemical and herbivore treatments. We also observed an indirect positive effect of oil on Spartina, via a direct negative effect on insect herbivores. Our findings suggest that multi-stressor effects in our model system, 1) are mixed but can be antagonistic more often than expected, a finding contrary to previous assumptions of primarily synergistic effects, 2) can vary in duration, 3) can be difficult to discern a priori, and 4) can lead to ecological surprises through indirect effects with implications for coastal resilience. This leads us to conclude that understanding the simultaneous effects of multiple stressors is critical for predicting foundation-species persistence, discerning ecosystem resilience, and managing and mitigating impacts on ecosystem services.

Diluted bitumen-induced alterations in aerobic capacity, swimming performance, and post-exercise recovery in juvenile sockeye salmon (Oncorhynchus nerka)

The transportation of heavy crudes such as diluted bitumen (dilbit) sourced from Canadian oil sands through freshwater habitat requires the generation of information that will contribute to risk assessments, spill modelling, management, and remediation for the protection of aquatic organisms. Juvenile sockeye salmon (Oncorhynchus nerka) were exposed acutely (96 h) or subchronically (28 d) to the water-soluble fraction (WSFd) of Cold Lake Blend dilbit at initial total polycyclic aromatic compound (TPAC) concentrations of 0, 13.7, 34.7, and 124.5 µg/L. A significant induction (>3-fold) of hepatic liver ethoxyresorufin-O-deethylase (EROD) activity was induced by 96 h in fish exposed to [TPAC] ≥ 34.7 µg/L and at ≥13.7 µg/L for a 28 d exposure. Exposure resulted in a typical physiological stress response and disturbance of ion homeostasis; this included elevations in plasma [cortisol], [lactate], [Na⁺], and [Cl^-], and significant reductions in muscle [glycogen]. Critical swimming speed (U_crit) was significantly reduced (28.4%) in the acute exposure at [TPAC] 124.5 µg/L; reductions of 14.2% and 35.4% were seen in fish subchronically exposed at the two highest concentrations. Reductions in U_crit were related to significant reductions in aerobic scope (24.3-46.6%) at [TPAC]s of 34.7 and 124.5 µg/L, respectively. Exposure did not impair the ability to mount a secondary stress response following burst exercise, however, the time required for biochemical parameters to return to baseline values was prolonged. Alterations in critical systems supporting swimming, exercise recovery and the physiological stress response could result in decreased salmonid fitness and contribute to population declines if a dilbit spill occurs.

Assessing Fish Immunotoxicity by Means of In Vitro Assays: Are We There Yet?

There is growing awareness that a range of environmental chemicals target the immune system of fish and may compromise the resistance towards infectious pathogens. Existing concepts to assess chemical hazards to fish, however, do not consider immunotoxicity. Over recent years, the application of in vitro assays for ecotoxicological hazard assessment has gained momentum, what leads to the question whether in vitro assays using piscine immune cells might be suitable to evaluate immunotoxic potentials of environmental chemicals to fish. In vitro systems using primary immune cells or immune cells lines have been established from a wide array of fish species and basically from all immune tissues, and in principal these assays should be able to detect chemical impacts on diverse immune functions. In fact, in vitro assays were found to be a valuable tool in investigating the mechanisms and modes of action through which environmental agents interfere with immune cell functions. However, at the current state of knowledge the usefulness of these assays for immunotoxicity screening in the context of chemical hazard assessment appears questionable. This is mainly due to a lack of assay standardization, and an insufficient knowledge of assay performance with respect to false positive or false negative signals for the different toxicant groups and different immune functions. Also the predictivity of the in vitro immunotoxicity assays for the in vivo immunotoxic response of fishes is uncertain. In conclusion, the currently available database is too limited to support the routine application of piscine in vitro assays as screening tool for assessing immunotoxic potentials of environmental chemicals to fish.

Assessment of the effectiveness of a novel BioFilm-Membrane BioReactor oil-polluted wastewater treatment technology by applying biomarkers in the mussel Mytilus galloprovincialis

Petrochemical industries and oil refineries are sources of hazardous chemicals into the aquatic environments, and often a leading cause of reduced oxygen availability, thus resulting in adverse effects in biota. This study is an expansion of our previous work on the assessment of the BioFilm-Membrane Bioreactor (BF-MBR) to mitigate the impact of oil-polluted wastewater on marine environments. Specifically, this study evaluated the reduction of selected chemical constituents (hydrocarbons and trace metals) and toxicity related to hypoxia and DNA damage to mussels Mytilus galloprovincialis, before and after treatment of oil-polluted wastewater with the BF-MBR. The application of a multidisciplinary approach provided evidence of the efficiency of BF-MBR to significantly reducing the pollutants load from oily contaminated seawaters. As result, the health status of mussels was preserved by a hypoxic condition due to oily pollutants, as evidenced by the modulation in the gene expression of HIF-1α and PHD and changes in the level of hypotaurine and taurine. Moreover, ameliorative effects in the energy metabolism were also found in mussel gills showing increased levels of glycogen, glucose and ATP, as well as a mitigated genotoxicity was revealed by the Micronucleus and Comet assays. Overall, findings from this study support the use of the BF-MBR as a promising treatment biotechnology to avoid or limiting the compromise of marine environments from oil pollution.

Prior exposure to weathered oil influences foraging of an ecologically important saltmarsh resident fish

Estuarine ecosystem balance typically relies on strong food web interconnectedness dependent on a relatively low number of resident taxa, presenting a potential ecological vulnerability to extreme ecosystem disturbances. Following the Deepwater Horizon (DwH) oil spill disaster of the northern Gulf of Mexico (USA), numerous ecotoxicological studies showed severe species-level impacts of oil exposure on estuarine fish and invertebrates, yet post-spill surveys found little evidence for severe impacts to coastal populations, communities, or food webs. The acknowledgement that several confounding factors may have limited researchers’ abilities to detect negative ecosystem-level impacts following the DwH spill drives the need for direct testing of weathered oil exposure effects on estuarine residents with high trophic connectivity. Here, we describe an experiment that examined the influence of previous exposure to four weathered oil concentrations (control: 0.0 L oil m⁻²; low: 0.1 L oil m⁻²; moderate: 0.5–1 L oil m⁻²; high: 3.0 L oil m⁻²) on foraging rates of the ecologically important Gulf killifish (Fundulus grandis). Following exposure in oiled saltmarsh mesocosms, killifish were allowed to forage on grass shrimp (Palaeomonetes pugio) for up to 21 h. We found that previous exposure to the high oil treatment reduced killifish foraging rate by ~37% on average, compared with no oil control treatment. Previous exposure to the moderate oil treatment showed highly variable foraging rate responses, while low exposure treatment was similar to unexposed responses. Declining foraging rate responses to previous high weathered oil exposure suggests potential oil spill influence on energy transfer between saltmarsh and off-marsh systems. Additionally, foraging rate variability at the moderate level highlights the large degree of intraspecific variability for this sublethal response and indicates this concentration represents a potential threshold of oil exposure influence on killifish foraging. We also found that consumption of gravid vs non-gravid shrimp was not independent of prior oil exposure concentration, as high oil exposure treatment killifish consumed ~3× more gravid shrimp than expected. Our study findings highlight the sublethal effects of prior oil exposure on foraging abilities of ecologically valuable Gulf killifish at realistic oil exposure levels, suggesting that important trophic transfers of energy to off-marsh systems may have been impacted, at least in the short-term, by shoreline oiling at highly localized scales. This study provides support for further experimental testing of oil exposure effects on sublethal behavioral impacts of ecologically important estuarine species, due to the likelihood that some ecological ramifications of DwH on saltmarshes likely went undetected.

Discriminating source of oil contamination in teleost fish, Lates calcarifer, using multivariate analysis of a suite of physiological and behavioral biomarkers

The release of petroleum hydrocarbons into the environment from natural seeps, well blowouts, pipeline leaks, shipping accidents and deliberate tank washing poses an ongoing threat to marine ecosystems. Distinguishing the source of oil contamination in exposed biota can be relatively straightforward if samples of the oil are available but, in their absence, such discrimination in fish poses a major challenge. The use of physiological and behavioral biomarker analysis provides a useful tool to describe sub-lethal effects of toxicant exposure. In this study we describe the responses of 12 biomarkers in Lates calcarifer (Asian seabass) following a 33-day dietary exposure (1%w/w) to heavy fuel oil (HFO) and to Montara, a typical Australian medium crude oil (MCO). Principal components analysis was used to differentiate between fish exposed to HFO from those exposed to MCO. Inferences can be made about the composition of an oil from the biomarker profiles produced in exposed fish.

Nest survival of Seaside Sparrows (Ammospiza maritima) in the wake of the Deepwater Horizon oil spill

In 2010, the Deepwater Horizon oil spill released an estimated 4.9 million barrels of oil into the Gulf of Mexico, damaging coastal ecosystems. Seaside Sparrows (Ammospiza maritima)-a year-round resident of Gulf Coast salt marshes-were exposed to oil, as shown by published isotopic and molecular analyses, but fitness consequences have not been clarified. We monitored nests around two bays in Plaquemines Parish, Louisiana, USA from 2012-2017 to assess possible impacts on the nesting biology of Seaside Sparrows. A majority of nests failed (76% of known-fate nests, N = 252 nests, 3521 exposure-days) during our study, and predation was the main cause of nest failure (~91% of failed nests). Logistic exposure analysis revealed that daily nest survival rate: (1) was greater at nests with denser vegetation at nest height, (2) was higher in the more sheltered bay we studied, (3) decreased over the course of the breeding season in each year, and (4) was not correlated with either sediment polycyclic aromatic hydrocarbon concentrations or estimated predator abundance during the years for which we had those data. Although the Deepwater Horizon spill impacted other aspects of Seaside Sparrow ecology, we found no definitive effect of initial oiling or oiled sediment on nest survival during 2012-2017. Because predation was the overwhelming cause of nest failure in our study, additional work on these communities is needed to fully understand demographic and ecological impacts of storms, oil spills, other pollutants, and sea-level rise on Seaside Sparrows and their predators.

Immunotoxicity of Xenobiotics in Fish: A Role for the Aryl Hydrocarbon Receptor (AhR)?

The impact of anthropogenic contaminants on the immune system of fishes is an issue of growing concern. An important xenobiotic receptor that mediates effects of chemicals, such as halogenated aromatic hydrocarbons (HAHs) and polyaromatic hydrocarbons (PAHs), is the aryl hydrocarbon receptor (AhR). Fish toxicological research has focused on the role of this receptor in xenobiotic biotransformation as well as in causing developmental, cardiac, and reproductive toxicity. However, biomedical research has unraveled an important physiological role of the AhR in the immune system, what suggests that this receptor could be involved in immunotoxic effects of environmental contaminants. The aims of the present review are to critically discuss the available knowledge on (i) the expression and possible function of the AhR in the immune systems of teleost fishes; and (ii) the impact of AhR-activating xenobiotics on the immune systems of fish at the levels of immune gene expression, immune cell proliferation and immune cell function, immune pathology, and resistance to infectious disease. The existing information indicates that the AhR is expressed in the fish immune system, but currently, we have little understanding of its physiological role. Exposure to AhR-activating contaminants results in the modulation of numerous immune structural and functional parameters of fish. Despite the diversity of fish species studied and the experimental conditions investigated, the published findings rather uniformly point to immunosuppressive actions of xenobiotic AhR ligands in fish. These effects are often associated with increased disease susceptibility. The fact that fish populations from HAH- and PAH-contaminated environments suffer immune disturbances and elevated disease susceptibility highlights that the immunotoxic effects of AhR-activating xenobiotics bear environmental relevance.

Environmental modulators of diluted bitumen effects in juvenile pink salmon (Oncorhynchus gorbuscha)

Recent and potential expansions in the transportation of diluted bitumen (dilbit) through marine terminals in coastal regions of British Columbia require the examination of potential risks to estuarine species such as Pacific salmon. The estuarine habitat of out-migrated pink salmon (Oncorhynchus gorbuscha) exhibits dynamic temperature and salinity regimes, possibly modifying dilbit exposure, bioavailability and/or its effects. To examine dilbit toxicity and its modification by environmental stressors, juvenile pinks were subchronically exposed for 3 months to the water-accommodated fraction (WAF) of Cold Lake Blend dilbit (winter) in seawater at three salinities (7, 14, and 28‰ [temperature 12.5 °C]) and three temperatures (8.5, 12.5, and 16.5 °C [salinity of 28‰]). Temperature and salinity alone did not affect any measured endpoints in control fish. Dilbit exposure induced higher mortality at high (16.5 °C) and low temperatures (8.5 °C) as well as at higher salinity (28‰) in fish exposed to the highest dilution of WAF [total polycyclic aromatic compounds (TPAC) = 128.9 μg/L]. A concentration-dependent reduction of growth was evident in fish exposed to the medium (TPAC = 97.3 μg/L) and high dilution of WAF at higher temperatures (12.5 and 16.5 °C) and high salinity (28‰). At 28‰, swimming performance (U_burst) was decreased in fish exposed to the highest concentration of dilbit at all 3 temperatures. Gill Na⁺-K⁺-ATPase activity, white muscle lactate, glycogen, and triglyceride concentrations were altered by dilbit exposure and modified by temperature and salinity. In addition, gene expression associated with phase I biotransformation, energy metabolism, mitochondrial activity, and inflammation showed significant upregulation with exposure and temperature stress. Dilbit exposure at PAC concentrations in the ppb range, affected pink salmon at the molecular, biochemical, and whole organism level; effects that were exacerbated by environmental temperature and salinity.

Exposure and Recovery of the Gulf Toadfish (Opsanus beta) to Weathered Deepwater Horizon Slick Oil: Impacts on Liver and Blood Endpoints

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants that can be responsible for a variety of deleterious effects on organisms. These adverse outcomes are relatively well studied, but at concentrations rarely found in the environment. Among the documented effects of sublethal acute PAH exposure are reductions in osmoregulatory capacity and immune function, and changes in the function of critical metabolic organs such as the liver. Gulf toadfish (Opsanus beta) were exposed to control seawater (0.006 µg tPAH₅₀ /L) or water accommodated fractions of Deepwater Horizon spill oil diluted to 3 flow-through exposure regimes (0.009, 0.059, and 2.82 µg tPAH₅₀ /L) for 7 d, with a recovery period of equal duration. We hypothesized that these chronic exposures would induce the aryl hydrocarbon receptor (AhR)-mediated pathways and result in significant impacts on markers of osmoregulatory, immune, and metabolic function. We further hypothesized that measurable reversal of these impacts would be observed during the recovery period. Our results indicate that activation of cytochrome P 450 (CYP)1A1 was achieved during exposure and reversed during the recovery phase. The only significant deviations from controls measured were a reduction in plasma glucose in fish exposed to medium and high levels of PAH after 7 d of exposure and a reduction in plasma osmolality fish exposed to high levels of PAHs after 7 d of recovery, when CYP1A1 messenger (m)RNA levels had returned to control levels. Our study illustrates a disconnect between the activation of CYP1A1 in response to environmentally realistic PAHs concentrations and several physiological endpoints and supports the idea that the AhR might not be associated with mediating osmoregulatory, immune, and metabolic changes in Gulf toadfish. Environ Toxicol Chem 2021;40:1075-1086. © 2020 SETAC.

Oxidative stress, biotransformation enzymes and histopathological alterations in Nile tilapia (Oreochromis niloticus) exposed to new and used automotive lubricant oil

Lubricant oils are among oil-based products that are not fully consumed during its use, thereby producing non-biodegradable residues which can cause contamination of natural systems. This study evaluated the toxicity of new and used lubricating oil (0.01 and 0.1 mL L^-1) in adult Nile tilapia (Oreochromis niloticus), by assessing the effects on oxidative stress, biotransformation enzymes (liver and gills), and histopathological alterations on hepatic and pancreatic tissues after 3 and 7 days of exposure. Results showed that 3-days exposure to 0.1 mL L^-1 of used and new lubricating oil increased the activity of superoxide dismutase (SOD) and malondialdehyde (MDA) levels in liver of O. niloticus, respectively. In gills, catalase (CAT) was decreased in fish exposed to 0.1 mL L^-1 of non-used oil after 3 days, but pronounced increases in CAT was detected after 7 days-exposure to both new and used oil. Shorter exposure to both concentrations of new and used oil also raised glutathione-S-transferase activity (GST) in gills. Ethoxyresorufin-O-deethylase (EROD) was induced in liver of fish exposed to 0.1 mL L^-1of used oil after 3 and 7 days, however a reduced response of this enzyme was detected in gills of animals from both oil treatments. In vitro analysis showed that hepatic EROD was inhibited by lubricating oil exposures, with more pronounced responses in treatments containing used oil. Hepatic lesions, such as cytoplasmic vacuolization, nuclei abnormally, changes in hepatocytes shape, steatosis, cholestasis, eosinophilic inclusions and necrosis were mainly increased by 7 days exposure to used lubricating oil at higher concentration.

Variation of Microbial Diversity in Catastrophic Oil Spill Area in Marine Ecosystem and Hydrocarbon Degradation of UCMs (Unresolved Complex Mixtures) by Marine Indigenous Bacteria

The study targeted an assessment of microbial diversity during oil spill in the marine ecosystem (Kaohsiung port, Taiwan) and screened dominant indigenous bacteria for oil degradation, as well as UCM weathering. DO was detected lower and TDS/conductivity was observed higher in oil-spilled area, compared to the control, where a significant correlation (R² = 1; P < 0.0001) was noticed between DO and TDS. The relative abundance (RA) of microbial taxa and diversities (> 90% similarity by NGS) were found higher in the boundary region of spilled-oily-water (site B) compared to the control (site C) and center of the oil spill area (site A) (B_RA/diversity > C_RA/diversity > A_RA/diversity). The isolated indigenous bacteria, such as Staphylococcus saprophyticus (CYCTW1), Staphylococcus saprophyticus (CYCTW2), and Bacillus megaterium (CYCTW3) degraded the C₁₀-C₃₀ including UCM of oil, where Bacillus sp. are exhibited more efficient, which are applicable for environmental cleanup of the oil spill area. Thus, the marine microbial diversity changes due to oil spill and the marine microbial community play an important role to biodegrade the oil, besides restoring the catastrophic disorders through changing their diversity by ecological selection and adaptation process.

Oiling of American white pelicans, common loons, and northern gannets in the winter following the Deepwater Horizon (MC252) oil spill

The Natural Resource Damage Assessment and Restoration Trustees for the Deepwater Horizon oil spill assessed the external oiling of migratory bird species dependent on open water in the Gulf of Mexico following the aforementioned spill. The assessment was designed to evaluate birds that use open water during the winter within 40 km of the Gulf shoreline. We focused on the American white pelican (Pelecanus erythrorhynchos), common loon (Gavia immer), and northern gannet (Morus bassanus). Point counts (pelican, loon) or strip transects (gannet) were used and each target species was assessed for oiling (unoiled, trace, light, moderate, or heavy amounts) and photographed. Due to distance at sighting and/or poor visibility, not all visible birds were assessed. The percentage of birds oiled varied by species, with the common loon being the highest (23.6%), followed by American white pelican (16.9%), and northern gannet (6.9%). Most of the American white pelicans and common loons had trace (83% and 72%, respectively) or light levels (11% and 24%, respectively) of oiling. The northern gannet had just trace levels of oiling. Some pelicans (6%) and loons (4%) had moderate amounts of oiling. Based on expert derived-mortality estimates and our estimates of oil exposure, we used Monte Carlo simulations to predict expected decreases of 2.5%, 4%, and 11% in the observed population for the northern gannet, American white pelican, and common loon, respectively. While these values are underestimates of the true values given the long time lag (10-12 months) between the oil spill and the assessment, these data represent some of the few estimates of exposure for these species and describe minimum risk estimates to these species.

Physiological disturbances in juvenile sockeye salmon (Oncorhynchus nerka) exposed to the water-soluble fraction of diluted bitumen

Current and proposed transcontinental pipelines for the transport of diluted bitumen (dilbit) from the Canadian oil sands traverse the coastal watersheds of British Columbia, habitat essential to Pacific salmonids. To determine the potential risks posed to these keystone species, juvenile sockeye (Oncorhynchus nerka; 1+ parr) were acutely (24-96 h) or subchronically (21-42 d) exposed to 4 concentrations of the water-soluble fraction (WSF) of unweathered Cold Lake Blend dilbit (initial total PAC concentrations: 0, 13.7, 34.7 and 124.5 μg/L) in a flow-through system. Dilbit effects on iono-osmoregulation, the physiological stress response, and the immune system were assessed by both biochemical and functional assays. Hydrocarbon bioavailability was evidenced by a significant induction of liver ethoxyresorufin-O-deethylase (EROD) activity in exposed fish. Acute and subchronic exposure significantly reduced gill Na⁺-K⁺-ATPase activity and resulted in lower plasma osmolality, Cl^-, and Na⁺ concentrations. Acute exposure to dilbit resulted in a classic physiological stress response, however at 21 d of exposure, plasma cortisol remained elevated while other measured parameters had returned to baseline values. A compromised immune system was demonstrated by a 29.5 % higher mortality in fish challenged with Vibrio (Listonella) anguillarum following dilbit exposure compared to unexposed controls. Exposure of juvenile salmonids to the WSF of dilbit (at TPAC concentrations at the ppb level) resulted in sublethal effects that included a classic physiological stress response, and alterations in iono-osmoregulatory homeostasis and immunological performance.

Restoration of common loons following the North Cape Oil Spill, Rhode Island, USA

Oil spills are a widespread problem in the marine environment and can have extensive acute and chronic adverse impacts to resident and migratory biota. On 19 January 1996, the North Cape oil tanker caught fire and grounded on the coast of Rhode Island resulting in the spill of 828,000 gal (3134 metric tonnes) of home heating oil. It resulted in the estimated death of nearly 2300 birds, including a projected 402 common loons (Gavia immer) and 12 red-throated loons (Gavia stellata). Based on existing demographic data, a resource equivalency analysis (REA) calculated that the total loss, as measured through dead adults and their foregone young over their expected lifetimes, was 2920 discounted loon-years. To generate compensatory loon years, it was initially estimated that 25 common loon nests would need protection from development for 100 years. Following a $3 million settlement with the parties responsible for the spill, we conducted surveys to identify the highest quality breeding loon habitat for protection. Monitoring efforts included 184 loon territories from 2000 to 2009, representing 866 loon territory-years on 70 lakes in four regions of Maine. To evaluate restoration effectiveness, an updated REA was conducted using productivity data collected from these surveys. Results from the updated REA indicated that were these site-specific data available when the REA was originally generated, 70 nests would have been required to offset the lost loon-years - this project permitted the protection of 119 nests. Future REAs should incorporate site specific productivity data whenever possible to most accurately scale restoration to injury. Ranking lake habitat quality further optimizes restoration effectiveness. Our results indicate breeding success was highest on 24-81 ha lakes and that emphasizing protection of lakes with loon territories in this size class is optimal. Our results demonstrate a need for site-specific restoration plans to achieve the greatest restoration benefits.

Polycyclic aromatic hydrocarbon and hypoxia exposures result in mitochondrial dysfunction in zebrafish

Organisms are routinely subjected to a variety of environmental and chemical perturbations simultaneously. Often, multi-stressor exposures result in unpredictable toxicity that occurs through unidentified mechanisms. Here, we focus on polycyclic aromatic hydrocarbons (PAHs) and hypoxia, two environmental and physiological stressors that are known to co-occur in the environment. The aim of this study was to assess whether interactive mitochondrial dysfunction resulted from co-exposures of PAHs and hypoxia. Zebrafish embryos were co-exposed to non-teratogenic concentrations of an environmental PAH mixture and hypoxia beginning at 6 hpf for an acute period of 24 h and afterwards were given either no recovery period, 45 min, 5 -hs, or 18 -hs of recovery time in clean conditions. Mitochondrial function and integrity were assessed through the use of both in ovo and in vitro assays. Hypoxia exposures resulted in drastic reductions in parameters relating to mitochondrial respiration, ATP turnover, and mitochondrial DNA integrity. PAH exposures affected ATP production and content, as well as mitochondrial membrane dynamics and lactate content. While PAH and hypoxia exposures caused a broad range of effects, there appeared to be very little interaction between the two stressors in the co-exposure group. However, because hypoxia significantly altered mitochondrial function, the possibility remains that these effects may limit an individual's ability to respond to PAH toxicity and therefore could cause downstream interactive effects.

The combined effects of salinity, hypoxia, and oil exposure on survival and gene expression in developing sheepshead minnows, Cyprinodon variegatus

The 2010 Deepwater Horizon oil spill released approximately 780 million liters of crude oil contaminating coastal habitats from Texas to Florida which are important habitats for many fish species during early life stages. These diverse habitats are also prone to rapid fluctuations in water quality, such as dissolved oxygen concentration and salinity. The consequence of combined exposure to crude oil and suboptimal environmental conditions during early life stage development of fish is still largely unknown. The objective of this project was to investigate the impacts of exposure to crude oil in combination with varying environmental stressors on developing Cyprinodon variegatus survival, growth, and gene expression. Three life stages (embryonic, post-hatch, and post-larval) were exposed to four nominal concentrations (6.25%, 12.5%, 50% and 100% with actual polycyclic aromatic hydrocarbon (PAH) concentrations ranging from 0 to 512 μg/L) of high energy water accommodated fractions (HEWAF) under different oxic (2.0 or >5.0 mg/L) and salinity (10 or 30 ppt) regimes at 30 °C for 48 h. We found that the post-larval developmental stage was the most sensitive to oil toxicity. Median lethal concentrations during the post-larval exposures followed a treatment-dependent pattern with the highest mortality observed under hypoxic-high salinity conditions (64.55 μg/L). Real-time PCR analysis identified down regulation of target genes, encoding cytochrome P450-1α (cyp1a1), erythropoietin (epo), and the aryl hydrocarbon receptor nuclear translocator (arnt1) only when oil exposure occurred under hypoxic-high salinity conditions in treatments with PAH concentrations greater than 226 μg/L. The target genes measured in this experiment are involved in the aryl hydrocarbon receptor signaling pathway which modulates metabolism of PAHs (a major component of crude oil), and the hypoxia inducible 1-α signaling pathway which is responsible for resilience to hypoxic stress, and it is known that disruption of these pathways can lead to an array of acute and chronic effects. Our results indicated that sheepshead minnow are most sensitive to oil exposure during the post-larval developmental stage. Survival data from this age-stage also indicate that oil toxicity response is exacerbated in hypoxic and high salinity environments. The increased mortality observed during the post-larval developmental stage might be attributed to the suppression of the aryl hydrocarbon receptor signaling and the hypoxia inducible 1-α signaling pathways which is evident in by the down-regulated expression of cyp1a1, epo, and arnt1. These findings provide more information about interactions between oil and abiotic factors which enable us to make better assumptions of the ecological impacts of DWH on coastal estuaries.

Hypoxia and reduced salinity exacerbate the effects of oil exposure on sheepshead minnow (Cyprinodon variegatus) reproduction

Estuaries of the northern Gulf of Mexico are dynamic environments, with fluctuations in salinity and dissolved oxygen, including areas of seasonal hypoxia. Fish that reside and reproduce in these estuaries, including sheepshead minnow (Cyprinodon variegatus; SHM), were at significant risk of oil exposure following the Deepwater Horizon oil spill. It is poorly understood how differences in environmental conditions during oil exposure impact its toxicity. The present study investigated the effects of crude oil high-energy water accommodated fraction (HEWAF) on SHM reproduction in three environmental scenarios (normoxic, hypoxic, and hypoxic with low salinity) to determine if differences in salinity (brackish vs low salinity) and dissolved oxygen (normoxia vs hypoxia) could exacerbate the effects of HEWAF-derived polycyclic aromatic hydrocarbons (PAHs). We observed that HEWAF exposure significantly increased liver somatic index of SHM compared to control, but this effect was not exacerbated by hypoxia or low salinity. HEWAF exposure also significantly decreased egg production and egg fertilization rate, but only in the hypoxic and hypoxic with low salinity scenarios. A significant correlation existed between body burdens of PAHs and reproductive endpoints, providing substantial evidence that oil exposure reduced reproductive capacity in SHM, across a range of environmental conditions. These data suggest that oil spill risk assessments that fail to consider other environmental stressors (i.e. hypoxia and salinity) may be underestimating risk.

Oil toxicity and implications for environmental tolerance in fish

Crude oil and its constituent chemicals are common environmental toxicants in aquatic environments worldwide, and have been the subject of intense research for decades. Importantly, aquatic environments are also the sites of numerous other environmental disturbances that can impact the endemic fauna. While there have been a number of attempts to explore the potential additive and synergistic effects of oil exposure and environmental stressors, many of these efforts have focused on the cumulative effects on typical toxicological endpoints (e.g. survival, growth, reproduction and cellular damage). Fewer studies have investigated the impact that oil exposure may have on the ability of exposed animals to tolerate typically encountered environmental stressors, despite the fact that this is an important consideration when placing oil spills in an ecological context. Here we review the available data and highlight potentially understudied areas relating to how oil exposure may impair organismal responses to common environmental stressors in fishes. We focused on four common environmental stressors in aquatic environments - hypoxia, temperature, salinity and acid-base disturbances - while also considering social stress and impacts on the hypothalamus-pituitary-interrenal axis. Overall, we believe the evidence supports treating the impacts of oil exposure on environmental tolerance as an independent endpoint of toxicity in fishes.

Cyanobacterial blooms in oil-contaminated subtidal sediments revealed by integrated approaches

Cyanobacteria are important primary producers on the surface of oceans and are susceptible to oil spills. However, their tolerance to oil and their roles in the bioremediation of crude oil remain elusive. We analysed the response of microbial communities to a simulated oil spill in estuarine sediment microcosms under a series of oil concentrations (0, 25, 125, and 250 g kg^-1 dry wt.). Cyanobacterial blooms only occurred on the sediment surface in the low oil (LO, 25 g kg^-1 dry wt.) group, and cyanobacteria grew from very small amounts to enriched levels according to an internal mechanism. The dominant phylotypes enriched in the oil-contaminated sediments on day 35 were Leptolyngbya, Oscillatoria, Arthrospira (Spirulina), Geitlerinema and Cyanothece, and the majority were capable of fixing nitrogen. Gammaproteobacterial blooms occurred during the early stage, and Oceanospirillales dominated the sediment surface. The annotation of unassembled metatranscriptomic data revealed an increase in nitrogen metabolism, particularly photosynthesis (antenna proteins) during the later stage, together with depletion of fatty acid metabolism. In summary, high concentrations of crude oil are toxic to cyanobacteria but can facilitate the emergence of cyanobacterial aggregation at low concentrations (crude oil concentration < 25 g kg^-1 dry wt.).

A novel method for the synergistic remediation of oil-water mixtures using nanoparticles and oil-degrading bacteria

Releases of crude oil and other types of oil from numerous sources can impose catastrophic physical, chemical, and biological effects on aquatic ecosystems. While currently-used oil removal techniques possess many advantages, they have inherent limitations, including low removal efficiencies and waste disposal challenges. The present study quantified the synergistic interactions of polyvinylpyrrolidone (PVP) coated magnetite nanoparticles (NP) and oil-degrading bacteria for enhanced oil removal at the laboratory scale. The results showed that at relatively high oil concentrations (375 mg L^-1), NP alone could remove approximately 70% of lower-chain alkanes (C9-C22) and 65% of higher-chain (C23-C26), after only 1 h, when magnetic separation of NP was used. Removal efficiency did not increase significantly after that, which was likely due to saturation of the NP with oil. Microbial bioremediation, using strains of oil-degrading bacteria, removed almost zero oil immediately but 80-90% removal after 24-48 h. The combination of NPs and oil-degrading bacterial strains worked effectively to remove essentially 100% of oil within 48 h or less. This was likely due to the sorption of oil components to NPs and their subsequent utilization by bacteria as a joint Fe and C source, although the mechanisms of removal require further testing. Furthermore, results showed that the emission of selected volatile organic compounds (VOCs) and semi volatile organic compounds (SVOCs) were reduced after addition of NPs and bacteria separately. When combined, VOC and SVOC emissions were reduced by up to 80%.

In Silico Computational Transcriptomics Reveals Novel Endocrine Disruptors in Largemouth Bass ( Micropterus salmoides)

In recent years, decreases in fish populations have been attributed, in part, to the effect of environmental chemicals on ovarian development. To understand the underlying molecular events we developed a dynamic model of ovary development linking gene transcription to key physiological end points, such as gonadosomatic index (GSI), plasma levels of estradiol (E2) and vitellogenin (VTG), in largemouth bass ( Micropterus salmoides). We were able to identify specific clusters of genes, which are affected at different stages of ovarian development. A subnetwork was identified that closely linked gene expression and physiological end points and by interrogating the Comparative Toxicogenomic Database (CTD), quercetin and tretinoin (ATRA) were identified as two potential candidates that may perturb this system. Predictions were validated by investigation of reproductive associated transcripts using qPCR in ovary and in the liver of both male and female largemouth bass treated after a single injection of quercetin and tretinoin (10 and 100 μg/kg). Both compounds were found to significantly alter the expression of some of these genes. Our findings support the use of omics and online repositories for identification of novel, yet untested, compounds. This is the first study of a dynamic model that links gene expression patterns across stages of ovarian development.

Vascular parameters continue to decrease post-exposure with simultaneous, but not individual exposure to BPA and hypoxia in zebrafish larvae

How fish respond to hypoxia, a common stressor, can be altered by simultaneous exposure to pollutants like bisphenol A (BPA), a plasticizer. BPA is cardiotoxic and interferes with the hypoxia inducible factor pathway (HIF-1α), therefore disrupting the hypoxic response. Co-exposure to hypoxia and BPA also causes severe bradycardia and reduced cardiac output in zebrafish larvae. The purpose of this work was to determine how the cardiovascular effects of co-exposure vary with BPA concentration and persist beyond exposure. Zebrafish embryos were exposed to 0, 0.01, 0.1, 1, and 100 μg/L of BPA during normoxia (>6.0 mg/L O₂) and hypoxia (2.0 ± 0.5 mg/L O₂) between 1 h post fertilization (hpf) and late hatching (72-96 hpf). Heart rate, cardiac output, and red blood cell (RBC) velocity were determined through video microscopy and digital motion analysis at late hatching and 10 days post fertilization (dpf), several days post exposure. In comparison to the hypoxic control, RBC velocity was 25% lower with 0.01 μg/L BPA and hypoxia at late hatching. At 10 dpf, the difference in RBC velocity between these treatments doubled, despite several days of recovery. This coincided with a 24% thinner outer diameter for caudal vein but no effect on cardiac or developmental parameters. Statistical interactions between BPA and oxygen concentration were found for arterial RBC velocity at both ages. Because the co-occurrence of both stressors is extremely common, it would be beneficial to understand how BPA and hypoxia interact to affect cardiovascular function during and after exposure.

Responses of immune organs after single-dose exposure to phenanthrene in yellowfin seabream (Acanthopagrus latus): CYP1A induction and oxidative stress

The effect of phenanthrene (Phe) on induction of ethoxyresorufinO-deethylase (EROD) activity and oxidative stress was examined in immune organs of yellowfin seabream Acanthopagrus latus. Fish were treated with a single intraperitoneal injection at 2, 20, or 40 mg kg^-1. The Phe concentration in spleen, EROD activity, superoxide dismutase (SOD) and catalase (CAT) activity, ascorbic acid (AsA), total glutathione (GSH), lipid peroxidation (LPO), and protein carbonylation (PC) levels in spleen and head kidney were assessed at one, four, seven, and 14 days post-injection. Dose response relationship was explored for data on day four. Phe concentration reached the highest observed level on day four, showed decline on day seven, and was undetectable at the end of trial. EROD activity in both organs followed the pattern of Phe level in all treated groups. Catalase and SOD activity at low Phe concentrations was significantly higher than controls, while LPO and PC level showed no differences from controls. In contrast, at 20 and 40 mg kg^-1, CAT and SOD activity, an indicator of oxidative stress, was significantly lower than in untreated controls, while AsA, GSH, LPO, and PC levels were higher on days 4 and 7. No parameter of any treatment group in either organ tissue showed difference from control values at the end of the experiment. The SOD and CAT activity in both organs exhibited a biphasic (initial stimulatory effect) effect, whereas other parameters showed a monophasic effect in terms of dose-response. Results suggest that Phe induced CYP1A and antioxidant responses in immune organs.

A non-destructive BFCOD assay for in vivo measurement of cytochrome P450 3A (CYP3A) enzyme activity in fish embryos and larvae

There is increasing interest in quantifying the exposure and effects of anthropogenic contaminants in fish. Determination of exposures in wild fish is routinely performed, but methods to investigate potential effects are less established. One of the most relevant approaches would be the use of in vivo assays, but existing assays are often limited to in vitro determination of enzyme activity. Many pharmaceuticals and some persistent pollutants activate, and are metabolized by cytochrome P4503A (CYP3A), which make it a relevant and desirable target for biomarker research. We altered the established 7-benzyloxy-4-trifluoromethylcoumarin-O-debenzylation (BFCOD) in vitro protocol for CYP3A activity determination, developing a rapid and inexpensive method to measure in vivo (and in ovo) CYP3A activity in two fish systems: Gulf killifish (Fundulus grandis) and zebrafish (Danio rerio) early life stages. Even with very low concentrations of 7-benzyloxy-4-trifluoromethyl coumarin (BFC, 0.06 µM or 20 µg/L), we were able to detect significant induction in CYP3A activity in embryos of F. grandis, as well as in larvae of D. rerio in response to benzo[a]pyrene (BaP) and fluoranthene (FL) exposures. Because of concerns regarding the possible contribution of CYP1A to BFCOD activity from previous research, we have used a CYP1A post-translational inhibitor (FL) in order to calculate the contribution of CYP1A to the BFCOD assay. We also dosed with benzo[k]fluoranthene (BkF) and showed significant induction of CYP1A activity, with no concurrent increase in CYP3A activity. In this paper, we have taken an established in vitro CYP3A activity assay, and utilized the reaction in a novel way to allow for the non-destructive determination of CYP3A. In summary, we describe a sensitive, cheap, fast and easy modified BFCOD assay for in ovo and in vivo determination of CYP3A activity for use in moderate throughput early-life-stage fish experiments.

I: Biomarker quantification in fish exposed to crude oil as input to species sensitivity distributions and threshold values for environmental monitoring

The aim of this study was to determine a suitable set of biomarker based methods for environmental monitoring in sub-arctic and temperate offshore areas using scientific knowledge on the sensitivity of fish species to dispersed crude oil. Threshold values for environmental monitoring and risk assessment were obtained based on a quantitative comparison of biomarker responses. Turbot, halibut, salmon and sprat were exposed for up to 8 weeks to five different sub-lethal concentrations of dispersed crude oil. Biomarkers assessing PAH metabolites, oxidative stress, detoxification system I activity, genotoxicity, immunotoxicity, endocrine disruption, general cellular stress and histological changes were measured. Results showed that PAH metabolites, CYP1A/EROD, DNA adducts and histopathology rendered the most robust results across the different fish species, both in terms of sensitivity and dose-responsiveness. The reported results contributed to forming links between biomonitoring and risk assessment procedures by using biomarker species sensitivity distributions.

Sublethal and Reproductive Effects of Acute and Chronic Exposure to Flowback and Produced Water from Hydraulic Fracturing on the Water Flea Daphnia magna

Hydraulic fracturing is an industrial process allowing for the extraction of gas or oil. To fracture the rocks, a proprietary mix of chemicals is injected under high pressure, which later returns to the surface as flowback and produced water (FPW). FPW is a complex chemical mixture consisting of trace metals, organic compounds, and often, high levels of salts. FPW toxicity to the model freshwater crustacean Daphnia magna was characterized utilizing acute (48 h median lethal concentrations; LC₅₀) and chronic (21 day) exposures. A decrease in reproduction was observed, with a mean value of 18.5 neonates produced per replicate over a 21 day chronic exposure to 0.04% FPW, which was a significant decrease from the average of 64 neonates produced in the controls. The time to first brood was delayed in the highest FPW (0.04%) treatment. Neonates exhibited an LC₅₀ of 0.19% of full-strength FPW, making them more sensitive than adults, which displayed an LC₅₀ value of 0.75%. Quantitative PCR highlighted significant changes in expression of genes encoding xenobiotic metabolism (cyp4) and moulting (cut). This study is the first to characterize chronic FPW toxicity and will help with the development of environmental monitoring and risk assessment of FPW spills.

Impacts of Petroleum-Derived Pollutants on Fish Development

The teleost fish embryo is particularly sensitive to petroleum hydrocarbons (polycyclic aromatic hydrocarbons, PAHs) at two distinct stages of development. The first is early during cleavage stages when PAHs alter normal signaling associated with establishment of the dorsal-ventral axis. This disruption involves the Wnt/β-catenin pathway and results in hyperdorsalized embryos that do not survive to hatching. The second, more sensitive period is during heart development, when oil and PAHs cause abnormal development of the heart as well as cardiac edema and arrhythmia. Even at extremely low levels (ng/L), PAHs cause subtle edema and altered contractility and heart rate, which impair swimming performance. Some PAHs are extremely phototoxic, such that exposures to trace concentrations result in severe membrane damage and mortality in sunlight. The developing fish embryo is a sensitive indicator of petroleum constituents in the environment, and healthy populations of fish likely require limited PAH exposure during development.

Physical condition and stress levels during early development reflect feeding rates and predict pre- and post-fledging survival in a nearshore seabird

The effects of acute environmental stressors on reproduction in wildlife are often difficult to measure because of the labour and disturbance involved in collecting accurate reproductive data. Stress hormones represent a promising option for assessing the effects of environmental perturbations on altricial young; however, it is necessary first to establish how stress levels are affected by environmental conditions during development and whether elevated stress results in reduced survival and recruitment rates. In birds, the stress hormone corticosterone is deposited in feathers during the entire period of feather growth, making it an integrated measure of background stress levels during development. We tested the utility of feather corticosterone levels in 3- to 4-week-old nestling brown pelicans (Pelecanus occidentalis) for predicting survival rates at both the individual and colony levels. We also assessed the relationship of feather corticosterone to nestling body condition and rates of energy delivery to nestlings. Chicks with higher body condition and lower corticosterone levels were more likely to fledge and to be resighted after fledging, whereas those with lower body condition and higher corticosterone levels were less likely to fledge or be resighted after fledging. Feather corticosterone was also associated with intracolony differences in survival between ground and elevated nest sites. Colony-wide, mean feather corticosterone predicted nest productivity, chick survival and post-fledging dispersal more effectively than did body condition, although these relationships were strongest before fledglings dispersed away from the colony. Both reproductive success and nestling corticosterone were strongly related to nutritional conditions, particularly meal delivery rates. We conclude that feather corticosterone is a powerful predictor of reproductive success and could provide a useful metric for rapidly assessing the effects of changes in environmental conditions, provided pre-existing baseline variation is monitored and understood.

Early life stages of an arctic keystone species (Boreogadus saida) show high sensitivity to a water-soluble fraction of crude oil

Increasing anthropogenic activities in the Arctic represent an enhanced threat for oil pollution in a marine environment that is already at risk from climate warming. In particular, this applies to species with free-living pelagic larvae that aggregate in surface waters and under the sea ice where hydrocarbons are likely to remain for extended periods of time due to low temperatures. We exposed the positively buoyant eggs of polar cod (Boreogadus saida), an arctic keystone species, to realistic concentrations of a crude oil water-soluble fraction (WSF), mimicking exposure of eggs aggregating under the ice to oil WSF leaking from brine channels following encapsulation in ice. Total hydrocarbon and polycyclic aromatic hydrocarbon levels were in the ng/L range, with most exposure concentrations below the limits of detection throughout the experiment for all treatments. The proportion of viable, free-swimming larvae decreased significantly with dose and showed increases in the incidence and severity of spine curvature, yolk sac alterations and a reduction in spine length. These effects are expected to compromise the motility, feeding capacity, and predator avoidance during critical early life stages for this important species. Our results imply that the viability and fitness of polar cod early life stages is significantly reduced when exposed to extremely low and environmentally realistic levels of aqueous hydrocarbons, which may have important implications for arctic food web dynamics and ecosystem functioning.

Is Exposure to Macondo Oil Reflected in the Otolith Chemistry of Marsh-Resident Fish?

Genomic and physiological responses in Gulf killifish (Fundulus grandis) in the northern Gulf of Mexico have confirmed oil exposure of resident marsh fish following the Macondo blowout in 2010. Using these same fish, we evaluated otolith microchemistry as a method for assessing oil exposure history. Laser-ablation inductively-coupled-plasma mass spectrometry was used to analyze the chemical composition of sagittal otoliths to assess whether a trace metal signature could be detected in the otoliths of F. grandis collected from a Macondo-oil impacted site in 2010, post-spill relative to pre-spill, as well as versus fish from areas not impacted by the spill. We found no evidence of increased concentrations of two elements associated with oil contamination (nickel and vanadium) in F. grandis otoliths regardless of Macondo oil exposure history. One potential explanation for this is that Macondo oil is relatively depleted of those metals compared to other crude oils globally. During and after the spill, however, elevated levels of barium, lead, and to a lesser degree, copper were detected in killifish otoliths at the oil-impacted collection site in coastal Louisiana. This may reflect oil contact or other environmental perturbations that occurred concomitant with oiling. For example, increases in barium in otoliths from oil-exposed fish followed (temporally) freshwater diversions in Louisiana in 2010. This implicates (but does not conclusively demonstrate) freshwater diversions from the Mississippi River (with previously recorded higher concentrations of lead and copper), designed to halt the ingress of oil, as a mechanism for elevated elemental uptake in otoliths of Louisiana marsh fishes. These results highlight the potentially complex and indirect effects of the Macondo oil spill and human responses to it on Gulf of Mexico ecosystems, and emphasize the need to consider the multiple stressors acting simultaneously on inshore fish communities.

Quantifying overlap between the Deepwater Horizon oil spill and predicted bluefin tuna spawning habitat in the Gulf of Mexico

Atlantic bluefin tuna (Thunnus thynnus) are distributed throughout the North Atlantic and are both economically valuable and heavily exploited. The fishery is currently managed as two spawning populations, with the GOM population being severely depleted for over 20 years. In April-August of 2010, the Deepwater Horizon oil spill released approximately 4 million barrels of oil into the GOM, with severe ecosystem and economic impacts. Acute oil exposure results in mortality of bluefin eggs and larvae, while chronic effects on spawning adults are less well understood. Here we used 16 years of electronic tagging data for 66 bluefin tuna to identify spawning events, to quantify habitat preferences, and to predict habitat use and oil exposure within Gulf of Mexico spawning grounds. More than 54,000 km² (5%) of predicted spawning habitat within the US EEZ was oiled during the week of peak oil dispersal, with potentially lethal effects on eggs and larvae. Although the oil spill overlapped with a relatively small portion of predicted spawning habitat, the cumulative impact from oil, ocean warming and bycatch mortality on GOM spawning grounds may result in significant effects for a population that shows little evidence of rebuilding.

Polycyclic aromatic hydrocarbons in blood related to lower body mass in common loons

We captured 93 wintering adult and subadult Common Loons (Gavia immer) in coastal Louisiana from 2011 to 2015 following the Deepwater Horizon oil spill. We tested blood samples for exposure to polycyclic aromatic hydrocarbons (PAHs) and measured physiological variables including hematocrit, hemoglobin and total blood protein. PAH concentrations in loon blood differed from year to year and by age class. High PAH concentrations were significantly related to lower body masses in both adult and subadult birds and higher serum protein levels in adults only. PAH concentrations had marginal relations with both hematocrit and hemoglobin levels. The types of PAHs detected also underwent a major shift over time. The PAHs detected in 2011, 2012, and 2015 were primarily low molecular weight (three carbon rings); however, in 2013, most detected PAHs were high molecular weight (four carbon rings). It is unclear what events led to the increase in PAH concentrations and the shift in type of PAHs over time.

Hypoxia depresses CYP1A induction and enhances DNA damage, but has minimal effects on antioxidant responses in sheepshead minnow (Cyprinodon variegatus) larvae exposed to dispersed crude oil

The growing incidence of hypoxic regions in coastal areas receiving high volumes of anthropogenic discharges requires more focused risk assessment of multiple stressors. One area needing further study is the combined effect of hypoxia and oil exposure. This study examined the short-term sublethal effects of co-exposure to hypoxia and water accommodated fractions (WAF) and chemically enhanced WAFs (CEWAFs) of Southern Louisiana Crude oil on detoxification, antioxidant defenses and genotoxicity in early life stage sheepshead minnow (Cyprinodon variegatus). CYP1A induction (evaluated by measuring EROD activity), activity of a number of key antioxidant enzymes (GST, GR, GPx, SOD, CAT, and GCL), levels of antioxidants (tGSH, GSH, and GSSG), evidence of lipid peroxidation (evaluated using the TBARS assay), and DNA damage (evaluated using the comet assay) provided a broad assessment of responses. Contaminant detoxification pathways induced by oil exposure were inhibited by co-exposure to hypoxia, indicating a maladaptive response. The interactive effects of oil and hypoxia on antioxidant defenses were mixed, but generally indicated less pronounced alterations, with significant increases in lipid peroxidation not observed. Hypoxia significantly enhanced DNA damage induced by oil exposure indicating the potential for significant deleterious effects post exposure. This study demonstrates the importance of considering hypoxia as an enhanced risk factor in assessing the effects of contaminants in areas where seasonal hypoxia may be prevalent.

Substantial changes in hemocyte parameters of Manila clam Ruditapes philippinarum two years after the Hebei Spirit oil spill off the west coast of Korea

Two years after the Hebei Spirit oil spill occurred off the west coast of Korea, we determined sub-lethal effects of the spilled oil on hemocyte parameters of Ruditapes philippinarum in the damaged areas. Clams in the spilled sites displayed unusually high proportion of granulocytes, which may result in higher phagocytosis capacity and reactive oxygen species production. Hemocytes in clams from the polluted sites also displayed less DNA damage and mortality than in the control site, possibly due to a faster phagocytosis of the impaired cells. Glycogen, the major energetic reserve, was depleted in clams from the spilled sites, potentially due to energetic consumption for maintenance of a large pool of granulocytes, detoxification processes and oxidative stress. Modified hemocyte parameters in clams in the spilled area, may reflect sub-lethal physiological stresses caused by the residual oils in the sediment, in conjunction with environmental modifications such as food availability and pathogens pattern.

Developmental abnormalities and differential expression of genes induced in oil and dispersant exposed Menidia beryllina embryos

Exposure of fish embryos to relatively low concentrations of oil has been implicated in sub-lethal toxicity. The objective of this study was to determine the effects of the exposure of Menidia beryllina embryos at 30-48h post-fertilization to the water accommodated fractions of oil (WAF, 200ppm, v/v), dispersants (20ppm, v/v, Corexit 9500 or 9527), and mixtures of oil and each of the dispersants to produce chemically enhanced water accommodated fractions (CEWAFs) over a 72-hour period. The polyaromatic hydrocarbon (PAH) and benzene, toluene, ethylene and xylene (BTEX) constituents of the 5X concentrated exposure solutions (control, WAF, dispersants and CEWAFs) were determined and those of the 1× exposures were derived using a dilution factor. PAH, BTEX and low molecular weight PAH constituents greater than 1ppb were observed in WAF and the dispersants, but at much higher levels in CEWAFs. The WAF and CEWAFs post-weathering were diluted at 1:5 (200ml WAF/CEWAF: 800ml 25ppt saltwater) for embryo exposures. Mortality, heartbeat, embryo normalcy, abnormality types and severities were recorded. The qPCR assay was used to quantify abundances of transcripts of target genes for sexual differentiation and sex determination (StAR, dmrt-1, amh, cyp19b, vtg and chg-L,), growth regulation (ghr) and stress response (cyp1a and Hsp90); and gapdh served as the housekeeping gene. Temperature was 21±1.5°C throughout the experimental period, while mortality was low and not significantly different (p=0.68) among treatments. Heartbeat was significantly different (0.0034) with the lowest heartbeats recorded in Corexit 9500 (67.5beats/min) and 9527 (67.1beats/min) exposed embryos compared with controls (82.7beats/min). Significantly more treated embryos were in a state of deterioration, with significantly more embryos presenting arrested tissue differentiation compared with controls (p=0.021). Exposure to WAF, dispersants and CEWAF induced aberrant expression of all the genes, with star, dmrt-1, ghr and hsp90 being significantly down-regulated in CEWAF and cyp19b in Corexit 9527. The cyp1a and cyp19b were significantly up-regulated in CEWAFs and WAF, respectively. The molecular endpoints were most sensitive, especially the expression of star, cyp19b, cyp1a, hsp90 and could therefore be used as early indicators of long term effects of Corexit 9500 and 9527 usage in oil spill management on M. beryllina, a valid sentinel for oil pollution events.

Spilled Oils: Static Mixtures or Dynamic Weathering and Bioavailability?

Polynuclear aromatic hydrocarbons (PAHs) from sequestered MV Selendang Ayu oil were biologically available in 2008, 3.6 y after it was spilled along Unalaska Island, Alaska. Thermodynamically driven weathering was the most probable mechanism of organism exposure to PAHs. Alkane and PAH composition in oil changed over time as smaller constituents were preferentially lost, indicative of weathering. In contrast, composition of the largest compounds (biomarkers) including triterpanes, hopanes, and steranes remained unchanged. Smaller molecules (the PAHs) lost from stranded oil were observed in indigenous mussels and passive samplers deployed in July 2008. Concentration and composition of PAHs were significantly different than in a non-oiled reference area and patterns observed in mussels were repeated in passive samplers deployed in three zones (intertidal, subtidal, and water). Thus, hydrocarbons lost from one compartment (sequestered whole oil) were detectable in another (mussels and passive samplers) implying aqueous transfer. Quantities of mobile oil constituents were small, yielding uptake concentrations that are likely inconsequential for mussels, but the sensitivity provided by bioaccumulation and passive sampler uptake ensured that dissolved hydrocarbons were detectable.

Hypoxia Enhances the Toxicity of Corexit EC9500A and Chemically Dispersed Southern Louisiana Sweet Crude Oil (MC-242) to Sheepshead Minnow (Cyprinodon variegatus) Larvae

Oil exploration and production activities are common in the northern Gulf of Mexico as well as many other coastal and near coastal areas worldwide. Seasonal hypoxia is also a common feature in the Northern Gulf, and many other coastal areas, which is likely to increase in severity and extent with continuing anthropogenic nutrient inputs. Hypoxia has well established physiological effects on many organisms, and it has been shown to enhance the toxicity of polycyclic aromatic hydrocarbons (persistent components of petroleum) in fish. The goal of this study was to examine the combined effects of hypoxia and exposure to contaminants associated with oil spills. We evaluated the effects of short term (48 hr) exposures to Corexit EC9500A, water accommodated fractions (WAF), and chemically enhanced water accommodated fractions (CEWAF) prepared from Southern Louisiana Sweet Crude Oil (MC 242) on survival of sheepshead minnow (Cyprinodon variegatus) larvae held under normoxic (ambient air) or hypoxic (2 mg/L O2) conditions. Results demonstrated that hypoxia significantly enhances mortality observed in response to Corexit or CEWAF solutions. In the latter case, significant interactions between the two stressors were also observed. Our data supports the need to further evaluate the combined stresses imparted by hypoxia and exposure to petroleum hydrocarbons and dispersants.

Joint effects of salinity and the antidepressant sertraline on the estuarine decapod Carcinus maenas

Concurrent exposure of estuarine organisms to man-made and natural stressors has become a common occurrence. Numerous interactions of multiple stressors causing synergistic or antagonistic effects have been described. However, limited information is available on combined effects of emerging pharmaceuticals and natural stressors. This study investigated the joint effects of the antidepressant sertraline and salinity on Carcinus maenas. To improve knowledge about interactive effects and potential vulnerability, experiments were performed with organisms from two estuaries with differing histories of exposure to environmental contamination. Biomarkers related to mode of action of sertraline were employed to assess effects of environmentally realistic concentrations of sertraline at two salinity levels. Synergism and antagonism were identified for biomarkers of cholinergic neurotransmission, energy production, anti-oxidant defences and oxidative damage. Different interactions were found for the two study sites highlighting the need to account for differences in tolerance of local ecological receptors in risk evaluations.

Genomic and genotoxic responses to controlled weathered-oil exposures confirm and extend field studies on impacts of the Deepwater Horizon oil spill on native killifish

To understand the ecotoxicological impacts of the Deepwater Horizon oil spill, field studies provide a context for ecological realism but laboratory-based studies offer power for connecting biological effects with specific causes. As a complement to field studies, we characterized genome-wide gene expression responses of Gulf killifish (Fundulus grandis) to oil-contaminated waters in controlled laboratory exposures. Transcriptional responses to the highest concentrations of oiled water in the laboratory were predictive of field-observed responses that coincided with the timing and location of major oiling. The transcriptional response to the low concentration (∼10-fold lower than the high concentration) was distinct from the high concentration and was not predictive of major oiling in the field. The high concentration response was characterized by activation of the molecular signaling pathway that facilitates oil metabolism and oil toxicity. The high concentration also induced DNA damage. The low concentration invoked expression of genes that may support a compensatory response, including genes associated with regulation of transcription, cell cycle progression, RNA processing, DNA damage, and apoptosis. We conclude that the gene expression response detected in the field was a robust indicator of exposure to the toxic components of contaminating oil, that animals in the field were exposed to relatively high concentrations that are especially damaging to early life stages, and that such exposures can damage DNA.

Physiological responses to shifts in multiple environmental stressors: relevance in a changing world

Population response to global change will depend on responses to a multivariate set of changes in abiotic habitat characteristics and biotic interactions. Organismal biologists seeking to make ecological inferences about the impacts of global change by studying physiological performance have traditionally performed carefully controlled experimental studies that examine one variable at a time. Those studies, while of high value, may not lead to accurate predictions of organismal responses in the natural habitat, where organisms experience concomitant changes in multiple environmental factors. The symposium "Physiological Responses to Simultaneous Shifts in Multiple Environmental Stressors: Relevance in a Changing World" focused on physiological studies in which multiple environmental variables were simultaneously examined and brought together an international group of early-career and established speakers with unique perspectives on studies of multistressors. In doing so, the objective of the symposium was to frame the necessary next steps for increasing predictive capacity of organismal responses to environmental shifts in the natural habitat, establish novel collaborations among researchers actively investigating physiological responses to a multivariate environment, and broaden the number of researchers conducting such studies.