Marine Blizzard

Norman Francis says it's all better now, though. So thank you, BP.

The problem with the sticky mix is not only that it suffocates life forms, she said. The BP oil droplets also still contain tiny amounts of toxic polycyclic aromatic hydrocarbons. If exposed to air at the ocean's surface or onshore, those chemicals might quickly evaporate or decompose, she said. But a mile below the Gulf surface, where there's low light, cold temperatures, and limited oxygen, the PAHs are surviving.

"There seems to be something about the matrix that is also not amenable to microbial oxidation" of the PAHs, she said. "We have yet to come up with a good explanation about why it isn't degrading."

Five years after the spill, deepwater coral continue to be affected, she said.

"Every time we've gone out, we've documented more limb loss and mortality," Joye said "It's a chronic problem. It's not just an acute, one-time exposure and the damage is done."