November 8, 2010
Oil Traveled Up the Gulf Food Chain, Scientists Say
Crude oil floating on the surface of the Gulf of Mexico in May.While officials in Washington pick apart the sequence of events that led to the release of nearly five million barrels of oil in the Deepwater Horizon disaster, scientists are still trying to figure out where all of that oil went.
Some of it was captured in the spill response, some of it is still visible in marshes and on beaches, some of it remains in plumes underwater and some of it evaporated, though there are still heated disputes over how much went where.
Meanwhile, a group of scientists in Alabama has been studying another pathway for all of that oil: through the Gulf of Mexico’s hungry oil-eating microbes. Scientists expected bacteria to eat the oil, but speculation remained about what would happen after that. As it turns out, the oil that the bacteria consumed traveled up the food chain as the oil-eating bacteria were eaten in turn, the scientists suggest.
By tracking oil’s particular carbon signature, which differs from the nutrients in the usual bacterial diet, scientists from the Dauphin Island Sea Lab in Alabama were able to observe the growing presence of oil in the planktonic food web as oil reached the waters of the northern gulf.
They describe their findings in a report published on Monday in Environmental Research Letters.
“We showed with little doubt that oil consumed by marine bacteria did reach the larger zooplankton that form the base of the food chain,” Monty Graham, the lead author of the report, said in a news release. These zooplankton are in turn eaten by larger marine organisms like fish and whales.
Dr. Graham added, “The continuing search for where the oil went should not only include direct evidence of existing pools of oil, but also the shadows of where the oil once was as indicated by so-called ‘biomarkers’ — such as light carbon isotopes in the bodies of plankton.”
The study did not look for toxicity in the food web; government scientists are studying that question. But it adds to the larger picture of the oil’s fate, providing evidence that much of the oil that “disappeared” was, to put it more precisely, eaten.