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The 2010 Deepwater Horizon (DWH) oil blowout in the Gulf of Mexico began on April 20, originating in the deep sea 66 km off the Louisiana coast. By early June, DWH oil had spread to coastal Louisiana, Mississippi, Alabama and western Florida. An estimated 2,113 km of shoreline were oiled, making DWH the largest marine oil spill in global history by length of affected shoreline. Additionally, a series of oil spill response measures were deployed, including diversions of Mississippi River discharge to forestall oil coming ashore, and the establishment of large-scale fishery closures, with both affecting coastal resources to varying degrees. Here, we review published studies and describe additional analyses evaluating long-term impacts of DWH on coastal/nearshore biological resources. We assembled time-series data collected by state, federal and academic partners on population abundance and environmental conditions to evaluate species and community change. Our study focused on plankton, invertebrates, fishes and dolphins, and 13 “key species” were selected to conduct semi-quantitative vulnerability-resilience (V-R) analyses. At one extreme, early life stages of Gulf Menhaden (Brevoortia patronus) were not affected due to seasonal spawning and larval development preceding the spill. In contrast, demographically independent populations of the common Bottlenose Dolphin, (Tursiops truncatus) suffered a variety of severe and ongoing health effects owing to oil exposure. Virtually all of the heavily oiled salt marsh habitat was in Louisiana, with the majority occurring in Barataria Bay. Multispecies trawl survey abundances declined post-DWH throughout eastern coastal Louisiana but remained stable elsewhere. A regime shift in composition of Barataria Bay trawl survey catches occurred during and following the spill, the persistence of which was associated with long-term reductions in average salinity and increases in water clarity. In some cases, fishery closures were associated with measurable but ephemeral increases in abundance of some targeted and bycatch species. Freshwater flooding of marshes was ineffective in preventing coastal oiling and severely affected benthic euryhaline resources including Eastern Oyster (Crassostrea virginica) and Marsh Periwinkle (Littoraria irrorata). The flooding response measure experiment also indicates the directionality of impacts that further planned water diversions may have on ecological communities of lower Mississippi River basins.

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The Deepwater Horizon oil spill revived discussions on the use of dispersants as an oil spill countermeasure. One of the greatest concerns regarding the use of dispersants deals with potential exposure of water column organisms to high concentrations of oil. While toxicity data on dispersants and physically and chemically dispersed oil have been generated for decades under controlled laboratory conditions, the practical use of this information has been limited by the lack of a centralized data repository. As a result, the Dispersant and Chemically Dispersed Oil Toxicity Database (DTox) was created to address that shared need of unrestricted and rapid access to toxicity data. DTox is a quantitative database that gathers existing toxicity data through a careful review and compilation of data extracted from the peer-review and gray literature. Through a rigorously evaluation of the quality of each data source, this database contains pertinent information including species scientific name, life stage tested, dispersant name, exposure type, oil weathering stage, exposure duration, etc. More importantly, this database contains effects concentrations reported on measured or nominal basis. Within the database, each data source is assigned an applicability score based on their relevance to oil spills. Key criteria in the determination of source applicability include exposure type, reported effects concentrations, 2 Abstract number 299546 2014 INTERNATIONAL OIL SPILL CONFERENCE 2and reported analytical chemistry. Information in DTox has been further integrated into a userfriendly tool that allows for on-the-fly data searches and data plotting in the form of Species Sensitivity Distributions. To date, +400 papers have been evaluated for potential inclusion into the database, and data extracted from +170 sources. Despite inherent limitations, existing toxicity data are of great value to the oil spill scientific community. Although toxicity data will never be enough to answer all toxicity questions regarding the use of dispersants, this centralized data repository can help inform decisions on dispersant use and can help identify data needs and gaps. The ultimate goal of this tool is its contribution to a better understanding of the biological effects of dispersants and oil in the aquatic environment.

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