title: Responses of the soft coral Xenia elongata following acute exposure to a chemical dispersant.
abstract: Limited toxicology data are available regarding oil dispersant exposure to coral species. Corexit® EC9500A (Corexit) is a commonly applied dispersant most well known for its use after the Deepwater Horizon spill in April, 2010. There is limited evidence that Corexit can cause a bleaching response in corals. The aims of the study were: (1) to determine the extent of bleaching after acute 24 h and 72 h exposures of sublethal concentrations (0-50 ppm) of Corexit to the pulsing soft coral Xenia elongata and (2) to investigate a percent symbiont loss calculation using zooxanthellae density. The percent symbiont loss calculation was compared to a traditional metric of normalizing zooxanthellae density to soluble protein content. Percent symbiont loss was an effective measure of coral stress in acute Corexit exposures, while protein normalized zooxanthellae density was more variable. The bleaching data suggest a positive relationship between dispersant concentration and percent symbiont loss, culminating in excessive tissue necrosis and coral mortality within 72 h in high concentration exposures (p < 0.001). Percent beaching ranged from 25% in 5 ppm exposures to 100% in 50 ppm exposures. Corexit also caused a significant decrease in pulse activity (p < 0.0001) and relative oxygen saturation (p < 0.001), possibly indicating a reduction in photosynthetic efficiency. This study and other similar research indicate that dispersant exposure is highly damaging to marine organisms, including ecologically important coral species.
authors.affiliation: Department of Biology, St. Mary's College of Maryland, 18952 E. Fisher Rd, 20686 St. Mary's City, MD USA ; Present Address: Harbor Branch Oceanographic Institute, Florida Atlantic University, 5600 N US Highway 1, 34946 Fort Pierce, FL USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Studivan
authors.affiliation: Department of Biology, St. Mary's College of Maryland, 18952 E. Fisher Rd, 20686 St. Mary's City, MD USA.
authors.forename: Walter I
authors.initials: WI
authors.lastname: Hatch
authors.affiliation: Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, PO Box 38, 20688 Solomons, MD USA.
authors.forename: Carys L
authors.initials: CL
authors.lastname: Mitchelmore
keywords: Coral bleaching; Corexit 9500; Oil dispersant; Percent symbiont loss; Xenia elongata