Abstract
On April 20, 2010, one of the largest offshore oil spills in history occurred with the blowout of the British Petroleum Deepwater Horizon (DWH) Macondo Prospect well. The well blowout and subsequent release of oil had the potential to impact the ecosystem of the Gulf of Mexico that harbors many significant resources. Accordingly, this study attempts to systematically evaluate and organize data, information, assumptions, and uncertainties regarding the DWH blowout using an ecological risk assessment approach. The analysis phase included toxicity tests of chemically enhanced water accommodated fraction (CEWAF) of MC252 crude oil and Corexit on the early life stages (ELS) of the red drum, Sciaenops ocellatus. The objectives of this study were threefold: (1) to characterize the toxicity of CEWAF of MC252 crude oil to red drum ELS, (2) determine how the sensitivity of this species compares to other finfish ELS; and (3) to determine if these laboratory results might be used to predict effects from in situ exposure to other commercially, recreationally and ecologically important finfish in the wake of the DWH blowout. Red drum ELS exposed for 24 hours to CEWAF with total polycyclic aromatic hydrocarbons (PAHs) ranging from 0.25 mg/L to 5.5 mg/L presented with one or more gross abnormalities including: cardiac edema, skeletal abnormalities, yolk sac edema, finfold abnormalities and decreased growth. The median concentration at which 50% of the red drum larvae experienced abnormalities (EC50) and were considered non-viable after 24 hour exposure to CEWAF ranged from 0.38 mg/L to 1.63 mg/L (n=2). The median lethal concentration (LC50) ranged from 0.48 mg/L to 2.43 mg/L (n = 2). The results of this study are in agreement with other toxicity tests using various finfish ELS native to the GOM, and show that the effects of MC252 CEWAF toxicity can be debilitating to individual finfish ELS. Population level effects to red drum and other sensitive finfish as a result of the DWH blowout would be dependent on the spatiotemporal severity of exposure particularly in relation to the timing of natural density-dependent population regulation.