A Decline in Benthic Foraminifera following the Deepwater Horizon Event in the Northeastern Gulf of Mexico

Sediment cores were collected from three sites (1000–1200 m water depth) in the northeastern Gulf of Mexico from December 2010 to June 2011 to assess changes in benthic foraminiferal density related to the Deepwater Horizon (DWH) event (April-July 2010, 1500 m water depth). Short-lived radioisotope geochronologies (²¹⁰Pb, ²³⁴Th), organic geochemical assessments, and redox metal concentrations were determined to relate changes in sediment accumulation rate, contamination, and redox conditions with benthic foraminiferal density. Cores collected in December 2010 indicated a decline in density (80–93%). This decline was characterized by a decrease in benthic foraminiferal density and benthic foraminiferal accumulation rate (BFAR) in the surface 10 mm relative to the down-core mean in all benthic foraminifera, including the dominant genera (Bulimina spp., Uvigerina spp., and Cibicidoides spp.). Cores collected in February 2011 documented a site-specific response. There was evidence of a recovery in the benthic foraminiferal density and BFAR at the site closest to the wellhead (45 NM, NE). However, the site farther afield (60 NM, NE) recorded a continued decline in benthic foraminiferal density and BFAR down to near-zero values. This decline in benthic foraminiferal density occurred simultaneously with abrupt increases in sedimentary accumulation rates, polycyclic aromatic hydrocarbon (PAH) concentrations, and changes in redox conditions. Persistent reducing conditions (as many as 10 months after the event) in the surface of these core records were a possible cause of the decline. Another possible cause was the increase (2–3 times background) in PAH’s, which are known to cause benthic foraminifera mortality and inhibit reproduction. Records of benthic foraminiferal density coupled with short-lived radionuclide geochronology and organic geochemistry were effective in quantifying the benthic response and will continue to be a valuable tool in determining the long-term effects of the DWH event on a larger spatial scale.     

Deep-Sea Benthic Footprint of the Deepwater Horizon Blowout

The Deepwater Horizon (DWH) accident in the northern Gulf of Mexico occurred on April 20, 2010 at a water depth of 1525 meters, and a deep-sea plume was detected within one month. Oil contacted and persisted in parts of the bottom of the deep-sea in the Gulf of Mexico. As part of the response to the accident, monitoring cruises were deployed in fall 2010 to measure potential impacts on the two main soft-bottom benthic invertebrate groups: macrofauna and meiofauna. Sediment was collected using a multicorer so that samples for chemical, physical and biological analyses could be taken simultaneously and analyzed using multivariate methods. The footprint of the oil spill was identified by creating a new variable with principal components analysis where the first factor was indicative of the oil spill impacts and this new variable mapped in a geographic information system to identify the area of the oil spill footprint. The most severe relative reduction of faunal abundance and diversity extended to 3 km from the wellhead in all directions covering an area about 24 km². Moderate impacts were observed up to 17 km towards the southwest and 8.5 km towards the northeast of the wellhead, covering an area 148 km². Benthic effects were correlated to total petroleum hydrocarbon, polycyclic aromatic hydrocarbons and barium concentrations, and distance to the wellhead; but not distance to hydrocarbon seeps. Thus, benthic effects are more likely due to the oil spill, and not natural hydrocarbon seepage. Recovery rates in the deep sea are likely to be slow, on the order of decades or longer.     

Metagenomics reveals sediment microbial community response to Deepwater Horizon oil spill

The Deepwater Horizon (DWH) oil spill in the spring of 2010 resulted in an input of ∼4.1 million barrels of oil to the Gulf of Mexico; >22% of this oil is unaccounted for, with unknown environmental consequences. Here we investigated the impact of oil deposition on microbial communities in surface sediments collected at 64 sites by targeted sequencing of 16S rRNA genes, shotgun metagenomic sequencing of 14 of these samples and mineralization experiments using ¹⁴C-labeled model substrates. The 16S rRNA gene data indicated that the most heavily oil-impacted sediments were enriched in an uncultured Gammaproteobacterium and a Colwellia species, both of which were highly similar to sequences in the DWH deep-sea hydrocarbon plume. The primary drivers in structuring the microbial community were nitrogen and hydrocarbons. Annotation of unassembled metagenomic data revealed the most abundant hydrocarbon degradation pathway encoded genes involved in degrading aliphatic and simple aromatics via butane monooxygenase. The activity of key hydrocarbon degradation pathways by sediment microbes was confirmed by determining the mineralization of ¹⁴C-labeled model substrates in the following order: propylene glycol, dodecane, toluene and phenanthrene. Further, analysis of metagenomic sequence data revealed an increase in abundance of genes involved in denitrification pathways in samples that exceeded the Environmental Protection Agency (EPA)''s benchmarks for polycyclic aromatic hydrocarbons (PAHs) compared with those that did not. Importantly, these data demonstrate that the indigenous sediment microbiota contributed an important ecosystem service for remediation of oil in the Gulf. However, PAHs were more recalcitrant to degradation, and their persistence could have deleterious impacts on the sediment ecosystem.     

Microbial community successional patterns in beach sands impacted by the Deepwater Horizon oil spill

Although petroleum hydrocarbons discharged from the Deepwater Horizon (DWH) blowout were shown to have a pronounced impact on indigenous microbial communities in the Gulf of Mexico, effects on nearshore or coastal ecosystems remain understudied. This study investigated the successional patterns of functional and taxonomic diversity for over 1 year after the DWH oil was deposited on Pensacola Beach sands (FL, USA), using metagenomic and 16S rRNA gene amplicon techniques. Gamma- and Alphaproteobacteria were enriched in oiled sediments, in corroboration of previous studies. In contrast to previous studies, we observed an increase in the functional diversity of the community in response to oil contamination and a functional transition from generalist populations within 4 months after oil came ashore to specialists a year later, when oil was undetectable. At the latter time point, a typical beach community had reestablished that showed little to no evidence of oil hydrocarbon degradation potential, was enriched in archaeal taxa known to be sensitive to xenobiotics, but differed significantly from the community before the oil spill. Further, a clear succession pattern was observed, where early responders to oil contamination, likely degrading aliphatic hydrocarbons, were replaced after 3 months by populations capable of aromatic hydrocarbon decomposition. Collectively, our results advance the understanding of how natural benthic microbial communities respond to crude oil perturbation, supporting the specialization-disturbance hypothesis; that is, the expectation that disturbance favors generalists, while providing (microbial) indicator species and genes for the chemical evolution of oil hydrocarbons during degradation and weathering.     

Interannual Recruitment Dynamics for Resident and Transient Marsh Species: Evidence for a Lack of Impact by the Macondo Oil Spill

The emulsification of oil at the Deepwater Horizon (DWH) well head relegated a large proportion of resultant hydrocarbon plumes to the deep sea, facilitated the incorporation of oil droplets into microbial and planktonic food web, and limited the severity of direct, wetland oiling to coastal Louisiana. Nevertheless, many transient fish and invertebrate species rely on offshore surface waters for egg and larval transport before settling in coastal habitats, thereby potentially impacting the recruitment of transient species to coastal nursery habitats quite distant from the well site. We compared the utilization of salt-marsh habitats by transient and resident nekton before and after the DWH accident using data obtained from an oyster reef restoration project in coastal Alabama. Our sampling activities began in the summer preceding the DWH spill and continued almost two years following the accident. Overall, we did not find significant differences in the recruitment of marsh-associated resident and transient nekton in coastal Alabama following the DWH accident. Our results, therefore, provide little evidence for severe acute or persistent oil-induced impacts on organisms that complete their life cycle within the estuary and those that spent portions of their life history in potentially contaminated offshore surface waters prior to their recruitment to nearshore habitats. Our negative findings are consistent with other assessments of nekton in coastal vegetated habitats and bolster the notion that, despite the presence of localized hydrocarbon enrichments in coastal habitats outside of Louisiana the most severe oil impacts were relegated to coastal Louisiana and the deep sea. Analyzing all the information learned from this accident will undoubtedly provide a synthesis of what has or has not been affected in the Northern Gulf of Mexico, which when put in context with oil spill studies elsewhere should improve our ability to avert and manage the negative consequences of such accidents.     

Microbial communities related to biodegradation of dispersed Macondo oil at low seawater temperature with Norwegian coastal seawater

The Deepwater Horizon (DWH) accident in 2010 created a deepwater plume of small oil droplets from a deepwater well in the Mississippi Canyon lease block 252 (‘Macondo oil’). A novel laboratory system was used in the current study to investigate biodegradation of Macondo oil dispersions (10 μm or 30 μm median droplet sizes) at low oil concentrations (2 mg l⁻¹) in coastal Norwegian seawater at a temperature of 4–5°C. Whole metagenome analyses showed that oil biodegradation was associated with the successive increased abundances of Gammaproteobacteria, while Alphaproteobacteria (Pelagibacter) became dominant at the end of the experiment. Colwellia and Oceanospirillales were related to n-alkane biodegradation, while particularly Cycloclasticus and Marinobacter were associated with degradation of aromatic hydrocarbons (HCs). The larger oil droplet dispersions resulted in delayed sequential changes of Oceanospirillales and Cycloclasticus, related with slower degradation of alkanes and aromatic HCs. The bacterial successions associated with oil biodegradation showed both similarities and differences when compared with the results from DWH field samples and laboratory studies performed with deepwater from the Gulf of Mexico.     

A Tale of Two Recent Spills—Comparison of 2014 Galveston Bay and 2010 Deepwater Horizon Oil Spill Residues

Managing oil spill residues washing onto sandy beaches is a common worldwide environmental problem. In this study, we have analyzed the first-arrival oil spill residues collected from two Gulf of Mexico (GOM) beach systems following two recent oil spills: the 2014 Galveston Bay (GB) oil spill, and the 2010 Deepwater Horizon (DWH) oil spill. This is the first study to provide field observations and chemical characterization data for the 2014 GB oil spill. Here we compare the physical and chemical characteristics of GB oil spill samples with DWH oil spill samples and present their similarities and differences. Our field observations indicate that both oil spills had similar shoreline deposition patterns; however, their physical and chemical characteristics differed considerably. We highlight these differences, discuss their implications, and interpret GB data in light of lessons learned from previously published DWH oil spill studies. These analyses are further used to assess the long-term fate of GB oil spill residues and their potential environmental impacts.     

Hydrocarbon-degrading bacteria enriched by the Deepwater Horizon oil spill identified by cultivation and DNA-SIP

The massive influx of crude oil into the Gulf of Mexico during the Deepwater Horizon (DWH) disaster triggered dramatic microbial community shifts in surface oil slick and deep plume waters. Previous work had shown several taxa, notably DWH Oceanospirillales, Cycloclasticus and Colwellia, were found to be enriched in these waters based on their dominance in conventional clone and pyrosequencing libraries and were thought to have had a significant role in the degradation of the oil. However, this type of community analysis data failed to provide direct evidence on the functional properties, such as hydrocarbon degradation of organisms. Using DNA-based stable-isotope probing with uniformly ¹³C-labelled hydrocarbons, we identified several aliphatic (Alcanivorax, Marinobacter)- and polycyclic aromatic hydrocarbon (Alteromonas, Cycloclasticus, Colwellia)-degrading bacteria. We also isolated several strains (Alcanivorax, Alteromonas, Cycloclasticus, Halomonas, Marinobacter and Pseudoalteromonas) with demonstrable hydrocarbon-degrading qualities from surface slick and plume water samples collected during the active phase of the spill. Some of these organisms accounted for the majority of sequence reads representing their respective taxa in a pyrosequencing data set constructed from the same and additional water column samples. Hitherto, Alcanivorax was not identified in any of the previous water column studies analysing the microbial response to the spill and we discuss its failure to respond to the oil. Collectively, our data provide unequivocal evidence on the hydrocarbon-degrading qualities for some of the dominant taxa enriched in surface and plume waters during the DWH oil spill, and a more complete understanding of their role in the fate of the oil.     

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

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

Benthic taxa as potential indicators of a deep-sea oil spill

The effect of the Deepwater Horizon oil spill on benthic macrofauna in the deep-sea Gulf of Mexico was measured in September–October 2010. Macrofauna community diversity and abundance were lowest closest to the wellhead and increased with distance from the wellhead up to 10 km. The macrofauna loss was primarily in surface sediments, which could be due to the deposition of oil and other toxic chemicals. Crustacean taxa appeared to be sensitive to the deep-sea blowout. Polychaete taxa varied in their sensitivity, but Dorvilleidae which is often associated with organic enrichment, was responsible for the largest amount of dissimilarity between stations close and far from the wellhead. Several other taxa were classified as sensitive or tolerant to the deep-sea blowout by comparing their distributions among impacted and non-impacted zones. The macrobenthic communities in the deep Gulf of Mexico exhibit a toxic response to the blowout on the Deepwater Horizon well, and this is correlated with barium and petroleum hydrocarbons.     

Diverse,rare microbial taxa responded to the Deepwater Horizon deep-sea hydrocarbon plume

The Deepwater Horizon (DWH) oil well blowout generated an enormous plume of dispersed hydrocarbons that substantially altered the Gulf of Mexico''s deep-sea microbial community. A significant enrichment of distinct microbial populations was observed, yet, little is known about the abundance and richness of specific microbial ecotypes involved in gas, oil and dispersant biodegradation in the wake of oil spills. Here, we document a previously unrecognized diversity of closely related taxa affiliating with Cycloclasticus, Colwellia and Oceanospirillaceae and describe their spatio-temporal distribution in the Gulf''s deepwater, in close proximity to the discharge site and at increasing distance from it, before, during and after the discharge. A highly sensitive, computational method (oligotyping) applied to a data set generated from 454-tag pyrosequencing of bacterial 16S ribosomal RNA gene V4–V6 regions, enabled the detection of population dynamics at the sub-operational taxonomic unit level (0.2% sequence similarity). The biogeochemical signature of the deep-sea samples was assessed via total cell counts, concentrations of short-chain alkanes (C₁–C₅), nutrients, (colored) dissolved organic and inorganic carbon, as well as methane oxidation rates. Statistical analysis elucidated environmental factors that shaped ecologically relevant dynamics of oligotypes, which likely represent distinct ecotypes. Major hydrocarbon degraders, adapted to the slow-diffusive natural hydrocarbon seepage in the Gulf of Mexico, appeared unable to cope with the conditions encountered during the DWH spill or were outcompeted. In contrast, diverse, rare taxa increased rapidly in abundance, underscoring the importance of specialized sub-populations and potential ecotypes during massive deep-sea oil discharges and perhaps other large-scale perturbations.     

Shifts in Symbiotic Endophyte Communities of a Foundational Salt Marsh Grass following Oil Exposure from the Deepwater Horizon Oil Spill

Symbiotic associations can be disrupted by disturbance or by changing environmental conditions. Endophytes are fungal and bacterial symbionts of plants that can affect performance. As in more widely known symbioses, acute or chronic stressor exposure might trigger disassociation of endophytes from host plants. We tested this hypothesis by examining the effects of oil exposure following the Deepwater Horizon (DWH) oil spill on endophyte diversity and abundance in Spartina alterniflora – the foundational plant in northern Gulf coast salt marshes affected by the spill. We compared bacterial and fungal endophytes isolated from plants in reference areas to isolates from plants collected in areas with residual oil that has persisted for more than three years after the DWH spill. DNA sequence-based estimates showed that oil exposure shifted endophyte diversity and community structure. Plants from oiled areas exhibited near total loss of leaf fungal endophytes. Root fungal endophytes exhibited a more modest decline and little change was observed in endophytic bacterial diversity or abundance, though a shift towards hydrocarbon metabolizers was found in plants from oiled sites. These results show that plant-endophyte symbioses can be disrupted by stressor exposure, and indicate that symbiont community disassembly in marsh plants is an enduring outcome of the DWH spill.     

Decline in condition of gorgonian octocorals on mesophotic reefs in the northern Gulf of Mexico: before and after the Deepwater Horizon oil spill

Hard-bottom ‘mesophotic’ reefs along the ‘40-fathom’ (73 m) shelf edge in the northern Gulf of Mexico were investigated for potential effects of the Deepwater Horizon (DWH) oil spill from the Macondo well in April 2010. Alabama Alps Reef, Roughtongue Reef, and Yellowtail Reef were near the well, situated 60–88 m below floating oil discharged during the DWH spill for several weeks and subject to dispersant applications. In contrast, Coral Trees Reef and Madison Swanson South Reef were far from the DWH spill site and below the slick for less than a week or not at all, respectively. The reefs were surveyed by ROV in 2010, 2011, and 2014 and compared to similar surveys conducted one and two decades earlier. Large gorgonian octocorals were present at all sites in moderate abundance including Swiftia exserta, Hypnogorgia pendula, Thesea spp., and Placogorgia spp. The gorgonians were assessed for health and condition in a before-after-control-impact (BACI) research design using still images captured from ROV video transects. Injury was modeled as a categorical response to proximity and time using logistic regression. Condition of gorgonians at sites near Macondo well declined significantly post-spill. Before the spill, injury was observed for 4–9 % of large gorgonians. After the spill, injury was observed in 38–50 % of large gorgonians. Odds of injury for sites near Macondo were 10.8 times higher post-spill, but unchanged at far sites. The majority of marked injured colonies in 2011 declined further in condition by 2014. Marked healthy colonies generally remained healthy. Background stresses to corals, including fishing activity, fishing debris, and coral predation, were noted during surveys, but do not appear to account for the decline in condition at study sites near Macondo well.     

Microbial community analysis of a coastal salt marsh affected by the Deepwater Horizon oil spill

Coastal salt marshes are highly sensitive wetland ecosystems that can sustain long-term impacts from anthropogenic events such as oil spills. In this study, we examined the microbial communities of a Gulf of Mexico coastal salt marsh during and after the influx of petroleum hydrocarbons following the Deepwater Horizon oil spill. Total hydrocarbon concentrations in salt marsh sediments were highest in June and July 2010 and decreased in September 2010. Coupled PhyloChip and GeoChip microarray analyses demonstrated that the microbial community structure and function of the extant salt marsh hydrocarbon-degrading microbial populations changed significantly during the study. The relative richness and abundance of phyla containing previously described hydrocarbon-degrading bacteria (Proteobacteria, Bacteroidetes, and Actinobacteria) increased in hydrocarbon-contaminated sediments and then decreased once hydrocarbons were below detection. Firmicutes, however, continued to increase in relative richness and abundance after hydrocarbon concentrations were below detection. Functional genes involved in hydrocarbon degradation were enriched in hydrocarbon-contaminated sediments then declined significantly (p<0.05) once hydrocarbon concentrations decreased. A greater decrease in hydrocarbon concentrations among marsh grass sediments compared to inlet sediments (lacking marsh grass) suggests that the marsh rhizosphere microbial communities could also be contributing to hydrocarbon degradation. The results of this study provide a comprehensive view of microbial community structural and functional dynamics within perturbed salt marsh ecosystems.     

胜利油田采油区土壤石油污染状况及其微生物群落结构

基于不同开采年代新油井(2011—)和老油井(1966—2003年)周边土壤的调查取样,研究了采油区土壤石油污染状况,利用PCR-DGGE和克隆测序技术,探讨了新、老油井周边土壤微生物的群落结构.结果表明:油井周边土壤均受到不同程度的石油污染,其石油烃含量大多高于土壤石油污染临界值(500 mg·kg^-1),且老油井周边土壤污染水平更高.污染土壤石油烃含量与土壤有机碳、全氮和速效钾含量呈显著正相关.老油井周边土壤微生物群落多样性指数随污染水平的增大而减小,新油井则呈相反的趋势.DGGE图谱优势条带测序结果表明,油井周边土壤均存在明显的优势菌,大多为石油烃相关菌和烃类降解菌,如微杆菌属、链霉菌属、迪茨氏菌属、黄杆菌属及α、γ变形菌等.
     

Patterns of biosynthesis and accumulation of hydrocarbons and contact sex pheromone in the female german cockroach,Blattella germanica

De novo synthesis of contact female sex pheromone and hydrocarbons in Blattella germanica was examined using short in vivo incubations. Accumulation of pheromone on the epicuticular surface and the internal pheromone titer were related to age-specific changes in hydrocarbon synthesis and accumulation in normal and allatectomized females. The incorporation of radiolabel from [1-¹⁴C]propionate into the cuticular methyl ketone pheromone fraction was positively related to corpora allata activity during two gonotrophic cycles. During peak pheromone production the total internal lipid fraction contained greater titers of pheromone than the cuticular surface, and it too exhibited a cycle internally, preceding the rise in external pheromone. This suggests that synthesis and accumulation of pheromone internally are followed by transport of pheromone to the epicuticular surface where it accumulates. Radiolabel was incorporated efficiently into both cuticular and internal hydrocarbons after the imaginal molt and until the peak of pheromone synthesis, but it declined to lower levels before ovulation and throughout pregnancy. The internal hydrocarbon titer decreased 58% after oviposition, suggesting deposition in the egg case. It remained relatively unchanged during pregnancy and increased again during the second gonotrophic cycle. In allatectomized females, hydrocarbon synthesis was reduced relative to control females until oviposition in the latter. However, subsequent rates of hydrocarbon synthesis in allatectomized females (without oothecae) exceeded the rates in sham-operated females (with oothecae). In the absence of ovarian uptake of hydrocarbons, the internal titer increased without the decline found in control females at oviposition. As internal hydrocarbons increased, so did cuticular hydrocarbons and both internal and cuticular methyl ketone pheromones. These patterns corresponded well with feeding patterns in sham-operated and allatectomized females, suggesting that pheromone production is normally regulated by stage-specific feeding-induced hydrocarbon synthesis (precursor accumulation internally) and juvenile hormoneinduced conversion of hydrocarbon to pheromone. They also suggest that both the cuticle and the ovaries might be target sites for hydrocarbon and possibly methyl ketone deposition. © 1994 Wiley-Liss, Inc.     

Beach sand oil spills select for generalist microbial populations

The specialization-disturbance hypothesis predicts that, in the event of a disturbance, generalists are favored, while specialists are selected against. This hypothesis has not been rigorously tested in microbial systems and it remains unclear to what extent it could explain microbial community succession patterns following perturbations. Previous field observations of Pensacola Beach sands that were impacted by the Deepwater Horizon (DWH) oil spill provided evidence in support of the specialization-disturbance hypothesis. However, ecological drift as well as uncounted environmental fluctuations (e.g., storms) could not be ruled out as confounding factors driving these field results. In this study, the specialization-disturbance hypothesis was tested on beach sands, disturbed by DWH crude oil, ex situ in closed laboratory advective-flow chambers that mimic in situ conditions in saturated beach sediments. The chambers were inoculated with weathered DWH oil and unamended chambers served as controls. The time series of shotgun metagenomic and 16S rRNA gene amplicon sequence data from a two-month long incubation showed that functional diversity significantly increased while taxonomic diversity significantly declined, indicating a decrease in specialist taxa. Thus, results from this laboratory study corroborate field observations, providing verification that the specialization-disturbance hypothesis can explain microbial succession patterns in crude oil impacted beach sands.Subject terms: Microbial ecology, Community ecology     

Benthic foraminifera associated with a hydrocarbon seep in the Rockall Trough (NE Atlantic)

Recent benthic foraminiferal assemblages in surface sediments of the Rockall Trough (NE Atlantic) have been qualitatively and quantitatively studied in order to investigate the effects of hydrocarbon seepage on benthic foraminiferal populations. Species diversity and abundance data have been examined in samples of similar lithology collected from hydrocarbon seep and non-seep (control) areas at a water depth of about 1000 m. Three species groups with different environmental preferences can be recognized. Group 1 dominates seep samples, and includes species tolerant to hydrocarbon emission, especially Angulogerina bradyana. In contrast, the less tolerant Group 2 species are weakly represented at seeps but dominate control samples. Group 3 species occur in low frequencies in both seep and non-seep samples. Furthermore, the measurement of species diversity (Shannon-Wiener and Simpson indices) demonstrates a difference in foraminiferal occurrence and frequencies between the seep and non-seep sites. Thus, the benthic foraminiferal distribution pattern is guided by different sensitivities of the species to hydrocarbons, reduced bottom-water oxygen usually associated with seepage and/or to a relatively elevated organic matter content in the sediment.     

Interannual patterns of the large free-living nematode assemblages in the Mexican Exclusive Economic Zone,NW Gulf of Mexico after the Deepwater Horizon oil spill

The presence and abundance of particular nematode genera in marine sediments are bioindicators of environmental disturbance. They can even reveal the existence of specific toxicants, such as trace-metals and hydrocarbons derived from fossil fuels. We studied this important infaunal component during a three-year monitoring program in Mexico’s Exclusive Economic Zone (EEZ) in the aftermath of a major oil spill in the northern Gulf of Mexico caused by the sinking of the Deepwater Horizon platform (DWH) in April of 2010. A closer look at the nematode composition and density values throughout and after the DWH oil spill revealed considerable changes. Continental shelf and upper slope sediments sampled in the summer of 2010 included 48 genera and a density of 44.45 ind/10 cm⁻². Eight months later in the winter of 2011, there was a critical decrement in genera number (23) and density (25.22 ind/10 cm⁻²). However, in 2012, the nematode community showed signs of recovery: genus diversity was 58 with a density of 91.45 ind/10 cm⁻². Significant differences were recorded between the first and the last sampling periods, driven by a remarkable turn-over in genera composition, and by an increase in density of the genera Sabatieria, Dorylaimopsis, and Cheironchus. Similarly, significant spatial differences between the nematofauna of the inner-middle shelf and the deepest zone (>2000 m) were detected. Correlation analyses confirmed the tolerant behavior of the above genera to Ni and Co, and their proliferation when hydrocarbon compounds presumably derived from the DWH oil spill increased throughout the study. The Maturity Index (MI) estimated for each survey ranged from 2.35 to 2.6. Environmental Quality Status conditions in the summer of 2010 were good while in the winter of 2011 were poor, and moderate towards the winter of 2012. Index of Trophic Diversity (ITD) values for each survey were high: 0.70, 0.68, and 0.74, respectively. A high predominance of feeding guilds 1B and 2B was recorded throughout the study.The estimated Index of Trophic Diversity (ITD) values resulted high (Table 5). These values apparently indicated that the four feeding types were proportionally distributed in the nematode assemblage. This fact was better reflected during the winter of 2012. Nonetheless, these results are not congruent with the high predominance of feeding guilds 1B and 2B observed throughout the study.     

Distribution of Petroleum and Aromatic Hydrocarbons at a Former Crude Oil and Natural Gas Production Facility

Site characterization and remediation activities were performed at a former crude oil and natural gas production facility prior to redevelopment of the site. Field activities included delineation, excavation and segregation of approximately 1,250,000 m³ of soil impacted by total petroleum hydrocarbons (TPH) and the aromatic volatile organic compounds (VOCs) benzene, toluene, ethylbenzene, and xylenes (hereafter, collectively referred to as BTEX). Petroleum hydrocarbon chain length information was used to determine whether remediation was required in impacted areas, because the site-specific cleanup values for TPH compounds, established by the California State Regional Water Quality Control Board (RWQCB), were based on hydrocarbon chain length. Site-specific cleanup levels were also established by the RWQCB for BTEX. Subsurface investigation activities performed at the site indicated that the mean percentage of condensate and TPH compounds in the gasoline range was significantly greater at depths ranging from 4.6 to 18 m than in shallower samples. There was no significant difference in the mean concentration of BTEX compounds and mean percentage of diesel range and heavier hydrocarbons with depth. The occurrence of BTEX, diesel range, and heavier hydrocarbons at depth may result from preferential pathways for downward migration of contaminants, including blown out wells, abandoned wellbores, and the presence of faults. Vapor phase diffusion may also be a major transport mechanism controlling movement of BTEX compounds beneath the site.