Evaluation of toxicity of Deepwater Horizon slick oil on spat of the oyster Crassostrea virginica.

The 2010 explosion of the Deepwater Horizon (DWH) oil rig generated the largest marine oil spill in US history with millions of barrels of crude oil released in the Gulf of Mexico (GoM). The eastern oyster, Crassostrea virginica, is an ecologically and economically important species in the northern GoM. Due to its biological characteristics (sessile, filter feeding), juvenile oysters may have been affected. This study investigated the effects of surface-collected DWH oil prepared as high-energy water-accommodated fraction (HEWAF) on the survival of 2-month-old oyster spat, and evaluated the potential impacts of HEWAF on particle clearance rate and spat tissue. Exposure of oysters to a range of oil/HEWAF (0-7-66-147-908-3450 μg tPAH50 (sum of 50 polycyclic aromatic hydrocarbons) L-1) resulted in non-dose-dependent mortalities and reduced clearance rates of algal food (Tisochrysis lutea). A morphometric study of the digestive tubules (DGTs) indicated a dose-dependent response to oil exposure on lumen dilation, on epithelium thinning of the DGT, and a significant change in DGT synchrony (LOEC = 66 μg tPAH50 L-1). This finding suggests that structural changes occurred in the digestive gland of exposed oysters most likely due to an oil-related stress. In addition, histological observations showed that tissues in contact with HEWAF (gills, palp, connective tissue, digestive gland) were adversely impacted at ≥ 7 μg tPAH50 L-1, and exhibited pathological symptoms typical of an inflammatory response (e.g., hemocyte diapedesis and infiltration, syncytia, epithelium sloughing).