The evidence is in, and investigators are charging the Gulf of Mexico oil plume with assault on at least one coral site.

The diffuse subsurface plume of oil and gas that escaped into the Gulf during the 2010 Deepwater Horizon oil spill was almost certainly a source for a brown muck found damaging a community of deep-sea corals near the wellhead, a group of scientists concluded today in a study published by the Proceedings of the National Academy of Sciences.

The scientists found the damaged coral 7 miles southwest of BP PLC's well during a research cruise in late 2010, a path similar to the course charted by the plume (Greenwire, Jan. 10). Many of the corals were coated in a flaky brown muck and showed signs of tissue damage. The spill was an immediate suspect, but proving the charge was uncharted territory.

"It is easy to see the impact of oil on surface waters, coastlines and marine life, but this was the first time we were diving to the seafloor to examine the effects on deep sea ecosystems," said Helen White, the study's lead author and a chemistry professor at Haverford College, in a statement.

The damaged coral community was a rare sight during their dives, the scientists stressed. They found all the corals located more than 12 miles from BP's well to be healthy during their first cruise, which ended in early November, several months after the well's demise. Only on their last dive did they discover the damaged site, which then demanded a second, short-notice cruise during December 2010.

What they saw during their cruise were coral skeletons stripped bare of their typical encrusting creatures, their tissues loose or strung with heavy mucus. Many of the corals were caked in a brown goo, unusual even in an ecosystem long accustomed to natural oil seeps. Almost 50 percent of the colonies showed damage to at least half their structure, and a quarter of the corals were almost wholly stressed or coated.

Although visual inspection of the coral took only a few weeks, the scientists then had to spend almost a year verifying whether the brown muck actually stemmed from the BP well. It was an arduous task, but the team, collaborating with oil fingerprinting experts at the Woods Hole Oceanographic Institution, eventually made a match.

In the end, it's an admirable case, said Dave Valentine, a microbial geochemist at the University of California, Santa Barbara, who was not affiliated with the study.

"If this were an episode of 'CSI,' the forensic evidence would be sufficient for an arrest," said Valentine, one of the foremost experts on the Gulf plume. "But even with this forensic evidence, many details of the oil's assault are unclear."

For the scientists to move forward, Valentine said, they'll need to answer a few more questions: How did the oil arrive at the corals? Why did it stick so well? What else is mixed into the mucus? How did the corals actually die?

Only then, he said, will the scientists be able to move from arrest to conviction.

Click here to read more about the study.