External effects of chemical dispersant and chemically dispersed oil on seabirds

Marine oil spills can have a significant impact to nearshore resources, including population-level effects to marine bird species. One potential response technique employed to reduce impacts is to apply chemical dispersants in... [ view full abstract ]

Marine oil spills can have a significant impact to nearshore resources, including population-level effects to marine bird species. One potential response technique employed to reduce impacts is to apply chemical dispersants in order to drive oil particles into the water column. Their use, however, is controversial due to lack of evidence on long-term ecosystem-level effects as well as the risk-benefit potential to animals caught in the release. To address the physical effects of this practice, 36 wild-caught common murres (Uria aalge) were randomly assigned to a control group or one of seven treatment groups exposed to increasing concentrations of chemical dispersant (Corexit 9500), Prudhoe Bay crude oil, or dispersed oil in water. After exposure, changes in behavior, body temperature, and water penetration through plumage were assessed over time in uncontaminated water. Additionally, two feathers plucked from the ventrum at each time point was microscopically assessed (e.g., distance between barbs, angle between barb and central rachis, and number of barbule clumps along barb) to determine structural changes to feathers. Significant differences were detected in body temperature, water penetration, and feather structure both across treatment groups and within treatment groups over time. Specifically, decreased body temperature, increased water penetration, and loss of buoyancy (with associated behavioral changes) was seen in groups exposed to contaminants in a dose-response manner immediately after exposure and extending to 48-hrs post-exposure. Statistically significant changes in barb distance and number of barbule clumps, however, was only associated with oil exposure. After 48-hrs, no significant differences in body temperature or water penetration was observed in groups exposed to dispersant only, but remained in groups exposed to oil and dispersed oil. The results of this study will provide tangible data to responders to better evaluate benefits/risks of chemical dispersant use with regard to seabirds during oil spills.