Lethal and sub-lethal effects of Deepwater Horizon slick oil and dispersant on oyster (Crassostrea virginica) larvae

• Deepwater Horizon oil spill coincided with oyster spawning and recruitment season.
• Different Crassostrea virginica larval stages were exposed to oil and/or Corexit for 72–96 h.
• HEWAF, CEWAF and Corexit reduced larval growth, settlement success and survival.
• Toxic effects were observed at environmentally relevant concentrations of tPAH50.
• Sublethal doses of PAH may impact oyster populations and the whole ecosystem.

In April 2010, crude oil was spilled from the Deepwater Horizon (DWH) oil platform for 87 days, coincident with the spawning season and recruitment of the oyster, Crassostrea virginica, in the Gulf of Mexico. Impacts of acute exposures to surface-collected DWH oil (HEWAF), dispersed oil (CEWAF) and dispersant alone (Corexit 9500A®) on planktonic larval stages of C. virginica (veliger, umbo and pediveliger) were tested in the laboratory. Exposures to HEWAF, CEWAF and dispersant were toxic to larvae impairing growth, settlement success and ultimately survival. Larval growth and settlement were reduced at concentrations of tPAH50 ranging from 1.7 to 106 μg L−1 for HEWAF and 1.1–35 μg L−1 for CEWAF, concentrations well within the range of water sampled during the DWH oil spill. Sublethal effects induced by oil and dispersant could have significant ecological implications on oyster populations and on the whole estuarine ecosystem.