Laboratory Exposures to Dispersed Oil in Fish, Shrimp and Crabs: Implications for Survival and Growth in Oil-Impacted Estuaries

The explosion of the Deepwater Horizon oil rig in the northern Gulf of Mexico on 20 April 2010 and the subsequent 87 day oil leak resulted in an unprecedented exposure of crude oil and dispersant to offshore, benthic, beach and estuarine habitats in Florida, Alabama, Mississippi and Louisiana.  Furthermore, the spill occurred during the reproductive season for many important nekton species, potentially impacting gonadal development, spawning, hatching success, and larval and juvenile growth and survival.  A series of laboratory experiments were conducted to evaluate the effects of oil and dispersant on sheepshead minnow (Cyprinodon variegatus) embryos, larvae and adults, blue crab (Callinectes sapidus) megalopae and Kona shrimp (Litopenaeus vannamei) juveniles.   A chemically enhanced water accommodated fraction (CEWAF) was produced by mixing artificial seawater, BP sweet crude oil taken from the riser pipe and Corexit 9500, the dispersant used by BP. Blue crab megalopae were exposed to 0%, 0.2%, 1.0%, 5.0% and 10.0% CEWAF under static renewal conditions for 96h.  The results showed that CEWAF is acutely toxic to blue crab megalopae, with a calculated 96 hour LC50 of 2.28% (95% CI = 1.50 – 3.48).  Juvenile shrimp were exposed to 0%, 0.2% and 5.0% CEWAF for 7 days with static renewal every 48 h.  Mortality (11%) occurred only at the highest dose within 24 h, and juveniles were lethargic upon initial and 48h renewal of the 5% CEWAF treatment. Embryonic (48 hours post fertilization, hpf) sheepshead minnow were exposed to 0%, 0.1% and 1.0% CEWAF under flow-through conditions and monitored through 14 days post hatch (dph).  Hatching success was significantly impacted by 1.0% CEWAF exposure beginning at 120 hpf, and at 216 hpf, 1.0% CEWAF produced approximately a 10% reduction in total hatch success.  At 14 dph, there was a significant, 10% reduction in larval length in both CEWAF treatments compared to controls.  Adult sheepshead minnow exposed to 0%, 0.1% and 1.0% CEWAF under flow-through conditions for 7 days showed a reduction in the ratio of vitellogenic oocytes:primary growth oocytes with increasing CEWAF concentrations and a significantly higher percentage of primary growth oocytes in the 1.0% CEWAF treatment.  Taken together, these results suggest that CEWAF significantly impacts survival of the youngest life stages of both crabs and fish and produces sub-lethal effects on older shrimp and fish. Thus, exposure to dispersed oil could have long-term population consequences for a variety of estuarine dependent species.