Gulf oil hits food chain much sooner than expected

Posted by Emma Woollacott

Following the Gulf oil spill, many people were surprised by how quickly the oil seemed to disappear. Now scientists say they know where it went - into the food chain.

Following the spill, about 200 million gallons of crude oil were released into the Gulf of Mexico. According to government and academic researchers, as much as half of this may have been naturally or chemically dispersed.

But the team at the Dauphin Island Sea Lab in Alabama decided to track a stable isotope of carbon from the oil and try and discover how quickly the rest oif it was being incorporated into the food-web - and how far up the chain it might have gone.

Dr Monty Graham and his colleagues showed that as the oil approached northern Gulf coastal waters in pulses, there was a dramatic decrease in the carbon isotope weight signature over about a four-week period - much more quickly than had been expected.

With all other possible sources of ‘light’ carbon ruled out, they concluded that oil-carbon entered the plankton food web as micro-organisms fed upon the oil-consuming bacteria. In fact, oil-carbon repeatedly showed up into August, well after the surface oil slicks were virtually gone.

According to Graham, it hadn't been disputed whether the oil would be consumed by marine bacteria - but there was debate on what this would ultimately mean for the rest of the food web.

"We showed with little doubt that oil consumed by marine bacteria did reach the larger zooplankton that form the base of the food chain. These zooplankton are an incredibly important food-source for many species of fish, jellyfish and whales," says Graham.

Graham says that this doesn't necessarily mean that crude oil toxins were transferred into the zooplankton, but it does show a food web pathway by which other components of the oil could reach higher in the food web.