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Deciphering the unseen, underwater effects of the Gulf oil spill.

The Gulf of Mexico oil spill sparked an explosion of sticky clumps of organic matter that scientists call sea snot, according to ongoing research.

The boom likely precipitated a sea-snot "blizzard" in Gulf (map) waters, researchers say. And as the clumps sank, they may have temporarily wiped out the base of the food chain in the spill region by scouring all small life from the water column.

In the weeks after the April 20 Deepwater Horizon oil rig explosion, scientists surveying the surface near the drill site spotted relatively huge particles—several centimeters across—of sea snot.

These particularly slimy flakes of "marine snow" are made up of tiny dead and living organic matter, according to Uta Passow, a biological oceanographer at the University of California, Santa Barbara.

Tiny plants in the ocean called phytoplankton produce a mucus-like substance when stressed, and it's possible that exposure to the Deepwater Horizon oil caused them to pump out more of the sticky stuff than usual.

This abundance of "mucus" made the naturally occurring marine-snow particles—usually about a few millimeters wide—even stickier.

"Everything they collide with in their path they collect and take with them," said project leader Passow, who's currently tracking marine snow aboard the research vessel Oceanus.

(Related: why the Gulf oil spill isn't going away.)

Sea Snot Spurred Marine "Snowfall"?

Based on surface observations and oily layers of dead plankton found on the seafloor, the researchers believe the sticky particles may have plummeted to the bottom of the ocean in a marine-snow "blizzard" around the Deepwater Horizon site in May. Passow cautioned, though, that no one actually witnessed the snowstorm.

In the lab Passow and colleagues are working to reproduce the marine-snow conditions that might have spawned the "huge, slimy" event, she said.

One simulation found that month-old marine snow would have sunk to the seafloor relatively fast—sinking hundreds of yards a day, compared with an average marine-snow sinking rate of 115 feet (35 meters) a day.

It's unknown why the material would have sunk so fast, Passow said. But it's possible the oil killed so many of the ocean's tiny floating organisms that the snow became abnormally heavy and so fell quicker than usual.

That heft may also explain why Passow and colleagues are finding so much new sea snot in the seafloor traps that they check every 36 hours—though nothing approaching the levels collected during the May snowstorm.

(Related: "Much Gulf Oil Remains, Deeply Hidden and Under Beaches.")

Recent observations by the team—including Vernon Asper and Arne Diercks of the University of Southern Mississippi—show no evidence of unusually voluminous sea snot at the surface nearly five months later, Passow noted.

The sea snot explosion, it seems, has come and gone, though its effects may linger. The sea snot blizzard "probably will have a long-term impact," Passow said—though exactly how the blizzard will affect the Gulf is anyone's guess.

(Read about the Gulf oil spill in the October National Geographic magazine.)

Sea Snot May Have Created Deadly Void

The possible long-term impact of the blizzard stems in part from its potential to starve or poison marine creatures.

By sinking en masse, the marine snow may have deprived fish larvae of a crucial food source—the phytoplankton itself. When fish larvae hatch, they have less than a day to find sustenance or they'll starve, Passow noted. (See pictures of ten animals at risk from the Gulf oil spill.)

On the Gulf seafloor, the sticky "snowstorm" may have killed bottom dwellers.

In addition to being perhaps suffocatingly large, the blizzard may have been toxic. Scientists have found tiny black dots in sediment traps near the BP spill site that—if confirmed as oil from the Gulf spill—suggest tarballs got swept up in the snowstorm.

Normally, dead organisms settling on the seafloor are free meal deliveries for animals living at depth. "But when it's oil-soaked particles, I suspect the bottom-dwelling organisms might not be so happy," marine-snow expert Alice Alldredge said.

(Also see "Toxic Oil Found Deep on Gulf Seafloor?")

Likewise, if tarballs were indeed caught up in the marine snow, their toxicity may be killing off various life-forms that hitchhike along with pockets of marine snow—each drifting pocket is usually a "hot spot of activity," project leader Passow said.

In any case, the true toll of the blizzard may remain a mystery in the short term.

Since many fish species mature slowly, for example, it will take a few years to determine whether the oily snowstorm caused a lost generation of certain species, said Alldredge, of the University of California, Santa Barbara, who was not involved in the research.

Likewise, the Gulf, in general, may take a while to fully recover. "Humans tend to want things to be fixed right away," she said, "and nature takes a little longer."

(Read more about how nature is fighting the oil spill.)

Sea Snot May Yield Giant Blobs of Mucus?

The addition of oil may cause the sea snot to coalesce into giant blobs called marine mucilage, which can grow more than a hundred miles (160 kilometers) long, according to Roberto Danovaro, director of the marine-science department at Italy's Polytechnic University of Marche.

(See "Giant, Mucus-Like Sea Blobs on the Rise, Pose Danger.")

Phytoplankton produce more mucus when there's more carbon and less nitrogen and phosphorus available—"exactly the case created by the oil spill," Danovaro said. An oil particle is mostly hydrogen and carbon.

In fact, because both the oil and the algae-generated mucus are gel-like, the apparently oily Gulf marine snow may be especially prone to forming marine-mucilage blobs, UCSB's Alldredge noted.

Such blobs are relatively common in oceans in spring and summer, and they move with the currents like "a submarine going up and down the water column," the Polytechnic University of Marche's Danovaro said. (See sea-mucus blob pictures.)

In rare cases, and if seas are consistently calm, mucilages can become very large and persist for months, allowing disease-causing bacteria to accumulate within the blobs. It's unknown whether that will happen in the Gulf, Danovaro said.

Even so, project leader Passow added, anything can happen. After all, she hadn't expected to find evidence of a marine-snow blizzard in the first place.