Sublethal effects of oil-contaminated sediment to early life stages of the Eastern oyster, Crassostrea virginica.

The explosion of the Deepwater Horizon (DWH) oil drilling rig resulted in the release of crude oil into the Gulf of Mexico. This event coincided with the spawning season of the Eastern oyster, Crassostrea virginica. Although oil bound to sediments constitutes an important source of polycyclic aromatic hydrocarbon (PAH) exposure to benthic organisms, toxicity of sediment-associated DWH oil has not been investigated in any bivalve species. Here, we evaluated the sublethal effects of acute exposure of gametes, embryos and veliger larvae of the Eastern oyster to different concentrations of unfiltered elutriates of sediment contaminated with DWH oil. Our results suggest that gametes, embryos and veliger larvae are harmed by exposure to unfiltered elutriates of contaminated sediment. Effective concentrations for fertilization inhibition were 40.6 µg tPAH50 L-1 and 173.2 µg tPAH50 L-1 for EC201h and EC501h values, respectively. Embryo exposure resulted in dose-dependent abnormalities (EC20 and EC50 values were 77.7 µg tPAH50 L-1 and 151 µg tPAH50 L-1, respectively) and reduction in shell growth (EC2024h value of 1180 µg tPAH50 L-1). Development and growth of veliger larvae were less sensitive to sediment-associated PAHs compared to embryos. Fertilization success and abnormality of larvae exposed as embryos were the most sensitive endpoints for assessing the toxicity of oil-contaminated sediment. Bulk of measured polycyclic aromatic hydrocarbons were sediment-bound and caused toxic effects at lower tPAH50 concentrations than high energy water accommodated fractions (HEWAF) preparations from the same DWH oil. This study suggests risk assessments would benefit from further study of suspended contaminated sediment.

Crude oil cardiotoxicity to red drum embryos is independent of oil dispersion energy.

The potential bioavailability of toxic chemicals from oil spills to water column organisms such as fish embryos may be influenced by physical dispersion along an energy gradient. For example, a surface slick with minimal wave action (low energy) could potentially produce different toxic effects from high energy situations such as pressurized discharge from a blown wellhead. Here we directly compared the toxicity of water accommodated fractions (WAFs) of oil prepared with low and high mixing energy (LEWAFs and HEWAFs, respectively) using surface oil samples collected during the 2010 Deepwater Horizon spill, and embryos of a representative nearshore species, red drum (Sciaenops ocellatus). Biological effects of each WAF type was quantified with several functional and morphological indices of developmental cardiotoxicity, providing additional insight into species-specific responses to oil exposure. Although the two WAF preparations yielded different profiles of polycyclic aromatic hydrocarbons (PAHs), cardiotoxic phenotypes were essentially identical. Based on benchmark thresholds for both morphological and functional cardiotoxicity, in general LEWAFs had lower thresholds for these phenotypes than HEWAFs based on total PAH measures. However, HEWAF and LEWAF toxicity thresholds were more similar when calculated based on estimates of dissolved PAHs only. Differences in thresholds were attributable to the weathering state of the oil samples.

Influence of variable ultraviolet radiation and oil exposure duration on survival of red drum (Sciaenops ocellatus) larvae.

The toxicity of some polycyclic aromatic hydrocarbons (PAHs) increases with ultraviolet (UV) radiation. The intensity of UV radiation varies within aquatic ecosystems, potentially providing reprieves during which tissue repair may occur. Transient/short-term PAH exposure prior to UV exposure may initiate metabolism/clearance, potentially affecting outcomes. Larval Sciaenops ocellatus were exposed to oil and UV radiation, using either variable photoperiods or pre-UV oil exposure durations. Shorter PAH exposures exhibited greater toxicity, as did exposure to shorter photoperiods. Environ Toxicol Chem 2018;37:2372-2379. © 2018 SETAC.

Exposure to Deepwater Horizon oil and Corexit 9500 at low concentrations induces transcriptional changes and alters immune transcriptional pathways in sheepshead minnows.

The 2010 Deepwater Horizon (DWH) oil spill caused the release of 4.9 million barrels of crude oil into the Gulf of Mexico, followed by the application of 2.9 million L of the dispersant, Corexit™ to mitigate the spread of oil. The spill resulted in substantial shoreline oiling, potentially exposing coastal organisms to polyaromatic hydrocarbon (PAH) and dispersant contaminants. To investigate molecular effects in fish following exposure to environmentally relevant concentrations of DWH oil and dispersants, we exposed adult sheepshead minnows (Cyprinodon variegatus) to two concentrations of high-energy water-accommodated fraction (HEWAF), chemically enhanced water-accommodated fraction (CEWAF) or Corexit 9500™ for 7 and 14days. Resulting changes in hepatic gene expression were measured using 8×15K microarrays. Analytical chemistry confirmed PAH concentrations in HEWAF and CEWAF treatments were low (ranging from 0.26 to 5.98µg/L), and likely representative of post-spill environmental concentrations. We observed significant changes to gene expression in all treatments (relative to controls), with Corexit and CEWAF having a greater effect on expression patterns in the liver than HEWAF treatments. Sub-network enrichment analysis of biological pathways revealed that the greatest number of altered pathways in high dose HEWAF and CEWAF treatments occurred following a 7-day exposure. Pathways related to immunity comprised the majority of pathways affected in each treatment, followed by pathways related to blood and circulation processes. Our results indicate that oil composition, concentration, and exposure duration all affect molecular responses in exposed fish, and suggest that low-concentration exposures may result in sub-lethal adverse effects.

Responses of juvenile southern flounder exposed to Deepwater Horizon oil-contaminated sediments.

The Deepwater Horizon oil spill released millions of barrels of crude oil into the northern Gulf of Mexico, much of which remains associated with sediments and can have continuing impacts on biota. Juvenile southern flounder (Paralichthys lethostigma) were exposed for 28 d in the laboratory under controlled conditions to reference and Deepwater Horizon oil-contaminated sediments collected from coastal Louisiana to assess the impacts on an ecologically and commercially important benthic fish. The measured polycyclic aromatic hydrocarbon (PAH) concentrations in the sediments ranged from 0.25 mg/kg to 3940 mg/kg suite of 50 PAH analytes (tPAH50). Mortality increased with both concentration and duration of exposure. Exposed flounder length and weight was lower compared to controls after 28 d of exposure to the sediments with the highest PAH concentration, but condition factor was significantly higher in these fish compared with all other treatments. Histopathological analyses showed increased occurrence of gill abnormalities, including telangiectasis, epithelial proliferation, and fused lamellae in flounder exposed to sediments with the highest tPAH50 concentrations. In addition, hepatic vascular congestion and macrovesicular vacuolation were observed in flounder exposed to the more contaminated sediments. These data suggest that chronic exposure to field collected oil-contaminated sediments results in a variety of sublethal impacts to a benthic fish, with implications for long-term recovery from oil spills. Environ Toxicol Chem 2017;36:1067-1076. © 2016 SETAC.

Effects of sediment amended with Deepwater Horizon incident slick oil on the infaunal amphipod Leptocheirus plumulosus.

Crude oil released from the Deepwater Horizon disaster into the Gulf of Mexico posed potential impacts to infaunal invertebrates inhabiting near shore habitats. The effects of sediment-associated weathered slick oil on the amphipod Leptocheirus plumulosus was assessed using 28-d exposures to total PAH sediment concentrations ranging from 0.3 to 24mg/kg (sum of 50 PAHs or tPAH50). Survival and growth rate were significantly decreased in the 2.6, 11.4 and 24.2mg/kg treatments, but only growth in 5.5mg/kg. Offspring production was dramatically decreased but was variable and significantly different only for 24.2mg/kg. The concentrations associated with 20% decreases relative to reference were 1.05 (95% CI=0-2.89) mg/kg tPAH50 for growth rate and 0.632 (95% CI=0.11-2.15) mg/kg tPAH50 for offspring production. The concentrations of PAHs affecting amphipods are within the range of concentrations measured in marsh areas reportedly impacted by DWH oil after its release.

Colony-specific cuticular hydrocarbon profile in Formica argentea ants.

The cuticular hydrocarbons of the ant Formica argentea were identified by gas chromatography/mass spectrometry. Behavioral bioassays tested the role of each class of cuticular hydrocarbon in nestmate recognition, and statistical analyses looked for potential colony-specific signatures. The cuticular hydrocarbons of F. argentea consist of n-alkanes, alkenes, and methyl-branched alkanes. Behavioral bioassays demonstrated that changes in the alkene and methyl-branched alkane signature of F. argentea increased aggression, but changes in alkanes did not. Statistical analyses demonstrated that F. argentea workers present a colony-specific hydrocarbon profile based on their methyl-branched C(29) alkane signature. Using this signature alone, it is possible to group worker ants statistically by nest, suggesting that methyl-branched C(29) alkanes may be important in nestmate recognition for this species. These results support the idea that variation in positional isomers of cuticular hydrocarbons of the same carbon chain length may provide enough information for nestmate recognition. Although the addition of alkenes increased aggression in F. argentea, alkenes did not provide a colony-specific signature. This study reinforces the idea that investigators studying nestmate recognition should not examine cuticular hydrocarbon profiles as a whole but rather, should look for colony-specific signatures embedded in parts of the profile.

Eusocial evolution and the recognition systems in social insects.

Eusocial species, animals which live in colonies with a reproductive division of labor, typically have closed societies, in which colony members are allowed entry and nonmembers, including animals of the same species, are excluded. This implies an ability to discriminate colony members ("self") from nonmembers ("nonself"). We draw analogies between this type of discrimination and MHC-mediated cellular recognition in vertebrates. Recognition of membership in eusocial colonies is typically mediated by differences in the surface chemistry between members and nonmembers and we review studies which support this hypothesis. In rare instances, visual signals mediate recognition. We highlight the need for better understanding of which surface compounds actually mediate recognition and for further work on how differences between colony members and nonmembers are perceived.