Vulnerability and resilience of living marine resources to the Deepwater Horizon oil spill : an overview

Funding for the project was primarily provided by the Gulf of Mexico Research Initiative through several of its research centers.The 2010 Deepwater Horizon (DWH) oil well blowout in the Gulf of Mexico (GoM) was the largest and perhaps most consequential accidental marine oil spill in global history. This paper provides an overview of a Research Topic consisting of four additional papers that: (1) assemble time series data for ecosystem components in regions impacted by the spill, and (2) interpret temporal changes related to the vulnerability of species and ecosystems to DWH and the ensuing resilience to perturbation. Time series abundance data for many taxa pre-date DWH, often by decades, thus allowing an assessment of population- and community-level impacts. We divided the north central GoM into four interconnected “eco-types”: the coastal/nearshore, continental shelf, open-ocean pelagic and deep benthic. Key taxa in each eco-type were evaluated for their vulnerability to the circumstances of the DWH spill based on population overlap with oil, susceptibility to oil contamination, and other factors, as well their imputed resilience to population-level impacts, based on life history metrics, ecology and post-spill trajectories. Each taxon was scored as low, medium, or high for 13 vulnerability attributes and 11 resilience attributes to produce overall vulnerability and resilience scores, which themselves were also categorical (i.e., low, medium, or high). The resulting taxon-specific V-R scores provide important guidance on key species to consider and monitor in the event of future spills similar to DWH. Similar analyses may also guide resource allocation to collect baseline data on highly vulnerable taxa or those with low resilience potential in other ecosystems. For some species, even a decade of observation has been insufficient to document recovery given chronic, long-term exposure to DWH oil remaining in all eco-types and because of impacts to the reproductive output of long-lived species. Due to the ongoing threats of deep-water blowouts, continued surveillance of populations affected by DWH is warranted to document long-term recovery or change in system state. The level of population monitoring in the open-ocean and deep benthic eco-types has historically been low and is inconsistent with the continued migration of the oil industry to the ultra-deep (≥1,500 m) where the majority of leasing, exploration, and production now occurs.Publisher PDFPeer reviewe

Testing the Effect of MOSSFA (Marine Oil Snow Sedimentation and Flocculent Accumulation) Events in Benthic Microcosms

In multispecies experiments performed in microcosms with natural sediment, it was investigated how the presence of marine snow affects the fate and ecological impact of deposited oil residues. The response of different taxonomic groups like nematodes, foraminifera, crustaceans and molluscs onto the presence of marine snow with or without oil was compared with the impact of deposited oil residues without marine snow. Also the effect of the presence of marine snow on oil biodegradation and transfer of oil-derived compounds to selected biota was studied. Although not designed to mimic the specific deep sea conditions in the Gulf of Mexico, the outcome of the experiments gave new insights in how a MOSSFA event can affect the benthic community. In general the experiments indicate that at field realistic oil-derived compound concentrations, the adverse impact of the marine snow on the sediment surface has a stronger impact on the benthic ecosystem than the oil’s toxicity on its own. In addition, the presence of marine snow reduces the degradation of the oil and can create an exposure route for animals that consume oiled marine snow and thus potentially enhances the ecological impact further

Vulnerability and Resilience of Species and Ecosystems to Large-Scale Contamination Events: Lessons Learned from Deepwater Horizon

The Deepwater Horizon (DWH) event - the largest marine oil spill in global history - was associated in time with a complex and diverse set of ecosystem changes. Four major “ecotypes” including the open ocean pelagic, deep benthic, continental shelf, and coastal/inshore habitats were affected. Despite nearly 10 years since the event, not all resources have recovered to pre-spill levels and some are projected to take decades to perhaps a century or more to recover. Two major reservoirs of DWH oil remain in the environment (deep benthic and coastal wetlands); in some cases little oil weathering has occurred resulting in ongoing toxic contamination. Although containing a significant proportion of the majority of the Gulf’s biodiversity of fishes and benthos, prior to DWH the deep sea was particularly poorly studied. New information collected post-DWH indicates a widespread decline in mid-water fish and deep-water benthos species. Distribution shifts of open ocean delphinids coincided with the spill. Continental shelf resources impacted by the spill included many species of commercial and recreational fisheries importance. Shelf communities exhibited moderate to significant declines coincident with the spill. Recovery of shelf resources is complicated by increased lionfish abundance post-spill. Inshore resources (and particularly bottlenose dolphin, American oyster and blue crab) were impacted not only by oil pollution but countermeasures used to mitigate oil impacts, and especially the release of large quantities of fresh water into coastal marshlands. While some inshore resources have recovered, DWH impacts may have weakened the resiliency of some species and communities potentially making them more susceptible to a wide range of ongoing stressors including sea level rise, ocean warming, acidification, chronic toxic exposures and others. Long-term ecosystem remediation programs (e.g., marsh reconstruction) may very well have consequential impacts for a range of ecologically and economically important resources affected by DWH. The oil industry has been steadily moving to deeper waters of the Gulf. In 2018 more than half of Gulf oil was derived from the “ultra-deep” (e.g., \u3e 1,500 m). Thus there is an urgent need to better quantify the productivity and vulnerability of deep sea resources to future oil spills

Changes in Sediment Redox Conditions Following the BP DWH Blowout Event

Following the blowout of the Macondo well, a pulse in sedimentation resulted in changes in sedimentary redox conditions. This is demonstrated by downcore and temporal changes in the concentration of redox sensitive metals: Mn, Re, and Cd. Sediment cores collected in the NE Gulf of Mexico (GoM) reveal increased sedimentation after the Deepwater Horizon (DWH) blowout. The formation of mucous-rich marine snow in surface waters and subsequent rapid deposition to underlying sediments is the likely cause. Respiration of this material resulted in decreased pore-water oxygen concentration and a shoaled redoxcline, resulting in two distinct Mn peaks in sediments following the event, one typically in the top 10 mm, with the other at 20–30 mm. Most cores near the wellhead reveal this non-steady state behavior for up to two years after the event. Associated with the Mn minimum between the two Mn peaks, a modest (15–30%) enrichment of Re consistent with reducing sediments typically exists. A three-year time series of three stations following the event reveal that sediment Re increased 3–4 times compared to the pre-impact baseline value for two years, indicating sediments are increasingly more reducing for two years. In the third year, Re concentration decreased, suggesting a return towards pre-impact conditions. In select sites where the density of benthic foraminifera was determined, an assemblage-wide decrease occurred coincident with reducing conditions as determined by redox sensitive metals, demonstrating the important consequences of changing redox conditions on benthic ecosystems. Determination of redox sensitive metals will continue to constrain the temporal evolution of reducing conditions, which will serve to document the long-term effects of the spill, and the possible return to pre-event conditions

Changes in Sediment Redox Conditions Following the BP DWH Blowout Event

Following the blowout of the Macondo well, a pulse in sedimentation resulted in changes in sedimentary redox conditions. This is demonstrated by downcore and temporal changes in the concentration of redox sensitive metals: Mn, Re, and Cd. Sediment cores collected in the NE Gulf of Mexico (GoM) reveal increased sedimentation after the Deepwater Horizon (DWH) blowout. The formation of mucous-rich marine snow in surface waters and subsequent rapid deposition to underlying sediments is the likely cause. Respiration of this material resulted in decreased pore-water oxygen concentration and a shoaled redoxcline, resulting in two distinct Mn peaks in sediments following the event, one typically in the top 10 mm, with the other at 20–30 mm. Most cores near the wellhead reveal this non-steady state behavior for up to two years after the event. Associated with the Mn minimum between the two Mn peaks, a modest (15–30%) enrichment of Re consistent with reducing sediments typically exists. A three-year time series of three stations following the event reveal that sediment Re increased 3–4 times compared to the pre-impact baseline value for two years, indicating sediments are increasingly more reducing for two years. In the third year, Re concentration decreased, suggesting a return towards pre-impact conditions. In select sites where the density of benthic foraminifera was determined, an assemblage-wide decrease occurred coincident with reducing conditions as determined by redox sensitive metals, demonstrating the important consequences of changing redox conditions on benthic ecosystems. Determination of redox sensitive metals will continue to constrain the temporal evolution of reducing conditions, which will serve to document the long-term effects of the spill, and the possible return to pre-event conditions

A Synthesis of Deep Benthic Faunal Impacts and Resilience Following the Deepwater Horizon Oil Spill

The Deepwater Horizon (DWH) oil spill significantly impacted the northern Gulf of Mexico (nGoM) deep benthos (\u3e125 m water depth) at different spatial scales and across all community size and taxa groups including microbes, foraminifera, meiofauna, macrofauna, megafauna, corals, and demersal fishes. The resilience across these communities was heterogeneous, with some requiring years if not decades to fully recover. To synthesize ecosystem impacts and recovery following DWH, the Gulf of Mexico Research Initiative (GOMRI) Core 3 synthesis group subdivided the nGoM into four ecotypes: coastal, continental shelf, open-ocean, and deep benthic. Here we present a synopsis of the deep benthic ecotype status and discuss progress made on five tasks: (1) summarizing pre- and post-oil spill trends in abundance, species composition, and dynamics; (2) identifying missing data/analyses and proposing a strategy to fill in these gaps; (3) constructing a conceptual model of important species interactions and impacting factors; (4) evaluating resiliency and recovery potential of different species; and (5) providing recommendations for future long-term benthic ecosystem research programs. To address these tasks, we assessed time series to detect measures of population trends. Moreover, a benthic conceptual model for the GoM deep benthos was developed and a vulnerability-resilience analysis was performed to enable holistic interpretation of the interrelationships among ecotypes, resources, and stressors. The DWH oil spill underscores the overall need for a system-level benthic management decision support tool based on long-term measurement of ecological quality status (EQS). Production of such a decision support tool requires temporal baselines and time-series data collections. This approach provides EQS for multiple stressors affecting the GoM beyond oil spills. In many cases, the lessons learned from DWH, the gaps identified, and the recommended approaches for future long-term hypothesis-driven research can be utilized to better assess impacts of any ecosystem perturbation of industrial impact, including marine mineral extraction

Number of dominant genera with depth for each core and the corresponding BFAR.

<p>Areas where there are no data available are denoted “n.d.”.</p><p>Number of dominant genera with depth for each core and the corresponding BFAR.</p

Location of core sampling sites in the northeastern Gulf of Mexico with reference to the Deepwater Horizon.

<p>Location of core sampling sites in the northeastern Gulf of Mexico with reference to the Deepwater Horizon.</p