Deep sea coral, some of it thousands of years old, was coated when the oil-Corexit mixture settled to the bottom. Two recent studies demonstrate the toxic effect of Corexit and oil on coral. In the first, published in January, researchers exposed two species of coral larvae to crude, Corexit 9500, and combinations of the two. Exposure to medium and high concentrations of oil and Corexit “significantly decreased larval settlement and survival for both species,” the abstract said. “Exposure of coral larvae to oil spill related contaminants, particularly the dispersant Corexit 9500, has the potential to negatively impact coral settlement and survival.” The study concluded that, “The demonstrated effects of (oil and Corexit) strongly suggest that the use of dispersants to mitigate oil spills in the vicinity of coral reefs should be avoided.”
The second study, published in April, was co-authored by Steve Kolian, Scott Porter, and two other researchers. They looked at coral species growing on oil and gas platforms in the Gulf. Out of 125 coral colonies sampled, 60 percent showed“visible signs of polyp mortality” and were excluded from the study. Healthy colonies were placed in tanks. One species began releasing a cloudy white material for 14 hours. “Several hours later, the aquarium water turned brown and then black. After water changes, the water would change from light brown to black as the corals depurated oil,” the authors wrote. “The corals appeared to purge most of the material within 7 days, but continued to display retracted polyps, exuded mucus, and showed signs of tissue loss for another 5 days.” The paper referred to a “brown flocculent material” found on the surface of some corals, noting that biomarkers in the material matched those of oil from the BP well, MC-252. Further analysis of “hydrocarbon exudate” from the corals also showed a match with MC-252 oil.
After publication, Kolian received an email from Eugene Shinagree from the University of South Florida’s College of Marine Science, who concurred that “this was most certainly BP oil.” The fact that “corals at that depth contained oil is clear evidence the oil contained Corexit,” he added. “Without (Corexit), oil would have been restricted to surface waters above the zone of coral growth. In my experience coral mucus resists absorption of untreated crude oil even when totally submerged in oil.”
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