Researchers find more evidence that microbes ate BP oil in Gulf

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on November 08, 2010 at 5:10 PM, updated November 08, 2010 at 5:12 PM


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In a research paper published Monday morning in IOP Publishing's Environmental Research Letters, the scientists found that microscopic animals found drifting in Gulf waters, called zooplankton, contained a higher concentration of a lighter carbon atom than a heavier carbon atom, an indicator that the organisms they were eating had feasted on oil.

"The message we have is that a very large fraction of the oil had to have been consumed by microbes, which in turn are food for larger organisms," said William "Monty" Graham, senior marine scientist at the lab and lead author for the paper. "For the most part, it looks like the microbes came to the rescue as the oil came towards shore, and turned it into food."

The oil began its journey up the food chain when it was gobbled up by tiny bacteria no larger than one micron, researchers found. There are 25,400 microns in an inch.

The bacteria were then eaten by small single-cell organisms called nanoflagellates, which were in turn eaten by ciliates. Then came the zooplankton, which are large enough to be eaten by a wide variety of sea life, from crabs to whales.

The study was designed to explore how the oil disappeared from the water so quickly and to show other researchers how to track the oil by studying larger organisms in the food chain.

"The problem that I think a lot of people have is that they can't connect the dots between all this oil... being released, and that other than in some locations where it's being seen in marshes, so much of the oil is gone," Graham said. "The important point we are trying to make here is that the way to go forward is to look for the shadow of oil, the evidence of where the oil was at one time."

Oil contains a greater percentage of "carbon 12" atoms, also known as isotopes, than "carbon 13" atoms, which are heavier, Graham said. The heavier carbon atom contains an additional neutron.

The researchers used special nets to take samples of zooplankton at four locations on the shallow to moderately-deep Gulf shelf area along the Alabama coastline just east of Mobile, and at two sites in Mobile Bay. The samples were collected between early June and mid-August.

The study found that in the weeks after four waves of oil approached the Alabama shoreline, zooplankton in Gulf waters contained a greater percentage of lighter carbon atoms than the heavier carbon atoms. Graham said that's an indication that they had eaten smaller organisms that had gobbled up oil, because other zooplankton food sources do not contain the same percentage of lighter carbon atoms.

The new study did not test for the presence of toxic materials in the zooplankton. Such testing is being done by other researchers participating in a federal-state assessment of damages to natural resources.

Graham believes that those tests will find little, if any, evidence of toxic materials moving up the food chain, however. He believes different species of bacteria fed on the toxic substances contained in the oil, such as polycyclic aromatic hydrocarbons, and turned most of the material back into non-toxic materials.

"When that data comes out, I doubt seriously that anybody will find toxic components of oil in the larger plankton, unless it's microdroplets of oil."

The marine lab's study was supported by a grant from the National Science Foundation under its RAPID program for oil spill research. The work also was supported by the Alabama Department of Conservation and Natural Resources, the National Oceanic and Atmospheric Administration and BP's Gulf Research Initiative, which is a five-year grant program administered by an independent board to underwrite oil spill research.

The next step for the marine laboratory scientists, Graham said, is to confirm whether the dramatic increase in carbon in the Gulf caused by the oil spill actually translated into the creation of more of the zooplankton, or whether the oil may have reduced the growth of tiny plant species known of phytoplankton to the point where it offset the increases in zooplankton.

The lab has received a grant from BP's Gulf Research Initiative for that study, he said.

Mark Schleifstein can be reached at or 504.826.3327.