Worry Underwater: Oxygen Levels Drop as Oil Continues to Flow

June 23, 2010— -- Evidence of marine biologists' doomsday scenario thrashes in the Gulf waters as sharks crowd into shallow waters.

Marine biologists say the sea animals flee the spill zone the way others would flee a forest fire. With thousands of gallons of oil contaminating their natural habitats, marine creatures press into oil-free waters.

"Their habitat is shrinking, tens of thousands of square miles are affected, and animals moving away from them," said Mobi Salangi, director of the Institute for Marine Mammal Studies. "There are changes in food, the food they eat and their prey."

Plumes of dense oil in shallow waters, up to 50 feet below the surface, have sucked up oxygen. Tests by the Dauphin Island Sea Lab usually show oxygen levels in the shallow waters at nearly eight parts per million. They're now down to two parts per million -- four times lower than normal.

Sharks, crabs, sting rays, birds and dolphins are all crowding piers, from Panama Beach, Florida, to the coasts of Louisiana.

Feeding frenzies are common in the Gulf, but the sharks jostling the Alabama coast are now much larger and in much greater numbers.

Biologists told ABC News that the entire food chain had been disrupted -- partly from the mass of oil and partly because the oil has sapped the water of oxygen.

"What we're really witnessing may be a shift in the whole ecosystem feeding structure, the food web," said Bob Shipp, director of marine biology at the University of Southern Alabama. "It also may be altered permanently -- as we've seen in other parts of the world where these things happen."

The oil spill has disturbed plant life too. Algae cannot survive if there isn't enough oxygen in the water, and a loss of algae could damage the ecosystem and the fisheries that rely on marine life.

Scientists said the oil may also cause the sea creatures' chemo receptors -- which function as built-in GPS systems to detect carbon dioxide levels -- to go on the fritz.

Deepwater Oil Plumes Also Affect Oxygen Levels

Samantha Joye, a marine scientist at the University of Georgia, told The Associated Press that the underwater oil plumes have reduced oxygen in the waters, but that it would take months for the oxygen to reach levels harmful to fish and animals, unlike in shallow waters, where oxygen levels have decreased at higher rates.

Joye said oxygen concentrations have dropped about 2 percent every day in the deepwater oil plumes, thousands of feet underwater.

Methane, which is also leaking from the Deepwater Horizon, poses another threat to underwater wildlife, as it attracts microbes that consume oxygen, and scientists said that if methane and microbe levels rise too much, they could create zones of so little oxygen that hardly anything could survive.