22 Aug 2014
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Mote Study: BP Oil Spill Cleaning Chemical Kills Coral

A Mote Marine Laboratory study of the cleaning agent Corexit 9500 showed that the cleaning agent in BP oil spill disaster also caused great harm to coral.

Mote Study: BP Oil Spill Cleaning Chemical Kills Coral

A new report from Mote Marine Laboratory in Sarasota released Wednesday reports that cleanup efforts from the Deepwater Horizon oil rig disaster could be causing a real threat to fragile coral reefs.

The study focused on studying coral larvae and seeing how a dispersant that is used to cling to oil slicks and diffuse it from reaching shores could actually be just as toxic. The findings are published in the peer-reviewed journal PLOS ONE.

The 2010 BP disaster spilled more than 200 million gallons of oil into the Gulf of Mexico and responders used these dispersants, one called Corexit 9500, to prevent the oil from reaching beaches.

"Overall, these findings indicate that exposure of coral larvae to the dispersant Corexit 9500 is toxic and will result in loss of coral recruitment," the study states.

It turns out that the dispersant is just as harmful to certain marine life as the oil itself.

“Dispersant, and the mixture of oil and dispersant, may be highly toxic to coral larvae and prevent them from building new parts of the reef,” said Dr. Kim Ritchie, principal investigator on the emergency Protect Our Reefs grant supporting this study and manager of the Marine Microbiology Program at Mote. “In addition, our results support the growing knowledge that certain coral species may fare worse than others during oil spills.” 

Mote scientists looked to study the effects of two Florida Keys coral species—mustard hill coral and mountainous star coral—and placing larvae of these corals in different sets of solutions. 

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The test solutions include saltwater plus Dissolved Deepwater Horizon oil from the rig, weathered oil, Corexit 9500 and a final one with the oil and the Corexit 9500. The coral larvae was placed in various concentrations of solutions for 72 hours while the mountainous star coral larvae was tested in slowly diluted solutions during a 96-hour period, according to Mote.

As expected, the larvae exposed to oil died sooner than ones only in seawater, and the mountainous star coral had a lower chance of surviving in the lowest oil concentration tested of .49 parts per million diluted over that 96-hour window, according to the study.

Even worse was the Corexit 9500—the very chemical that many hoped would clean up the oil and save marine life. 

No mountainous star coral larvae settled or survived at the medium and high concentrations of 50 and 100 parts per million and no mustard hill coral larvae settled or survived at 100 parts per million.

The study says that most of the mountainous star coral didn't even survive the lowest concentration test of .86 parts per million.

What do these scientific measurements mean to the naked eye?

"Depending on the concentration, the higher the concentration of oil and dispersant, the more opaque it becomes.  With the dispersant only (Corexit 9500), there was little cloudiness and with the water soluble oil mixture (WAF) it was perfectly clear," said Dr. Dana Wetzel, manager of Mote's Environmental Laboratory for Forensics. So it's not exactly water that humans would be fond of interacting with either.

The water soluble oil mixture is the chemicals from the oil that are able to dissolve in water; oil has many different chemical components, Wetzel continued to explained.

Fresh oil from Deepwater Horizon also started killing the larvae within the first 24 hours, according to the study.

Ritchie led the investigation along with Wetzel, Dr. Gretchen Goodbody-Gringley, former Mote postdoctoral researcher who is now an instructor at Bermuda Institute of Ocean Sciences, and were conducted both in Sarasota and at the Mote Tropical Research Laboratory on Summerland Key.

"The decision to use dispersant chemicals poses trade-offs for oil spill responders. While a dispersed surface oil slick is rendered less likely to reach the shore, treatment of major oil spills with dispersant chemicals has been shown to result in significant environmental degradation as a result of increased hydrocarbon dissolution and surfactant toxicity," the team wrote in their study.

Wetzel said what this study does is provide information on how oil and dispersants effect coral larvae because that wasn't available before. Scientists have known how fish and shellfish were damaged though.

The Florida Keys coral were not directly affected by Deepwater Horizon, according to the study, but these types of coral are also found in the Northwestern Gulf closer to the oil rig, but those coral were not directly affected either, according to the study. 

Scientists believe, however, that oil exploration near Cuba could pose further harm.

“To understand how oil and dispersant could affect wild corals, more research is needed on their complex natural life cycles,” Ritchie said. “Coral larvae seem to settle with help from landing pads called ‘biofilms’ that are formed by microbes like marine bacteria. This delicate natural process might be interrupted by dispersant and its mixture with oil, so it’s important to know how it works in detail.”

BP settled in November with the federal government in for $4.5 billion for its role in the spill. Sarasota County hopes it can claim $5.25 million from the case. 

The owner of the rig itself, Transocean Ltd., was due in New Orleans federal court Wednesday to pay a $400 million settlement with the Justice Department for violating the Clean Water Act, the Associated Press reported

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