Response of deep-water corals to oil and chemical dispersant exposure

Cold-water corals serve as important foundation species by building complex habitat within deep-sea benthic communities. Little is known about the stress response of these foundation species yet they are increasingly exposed to anthropogenic disturbance as human industrial presence expands further into the deep sea. A recent prominent example is the Deepwater Horizon oil-spill disaster and ensuing clean-up efforts that employed chemical dispersants. This study examined the effects of bulk oil–water mixtures, water-accommodated oil fractions, the dispersant Corexit 9500A®, and the combination of hydrocarbons and dispersants on three species of corals living near the spill site in the Gulf of Mexico between 500 and 1100m depths: Paramuricea type B3, Callogorgia delta and Leiopathes glaberrima. Following short-term toxicological assays (0–96h), all three coral species examined showed more severe health declines in response to dispersant alone (2.3–3.4 fold) and the oil–dispersant mixtures (1.1–4.4 fold) than in the oil-only treatments. Higher concentrations of dispersant alone and the oil–dispersant mixtures resulted in more severe health declines. C. delta exhibited somewhat less severe health declines than the other two species in response to oil and oil/dispersant mixture treatments, likely related to its increased abundance near natural hydrocarbon seeps. These experiments provide direct evidence for the toxicity of both oil and dispersant on deep-water corals, which should be taken into consideration in the development of strategies for intervention in future oil spills.