NEW ORLEANS -- The oil you can't see could be as bad as the oil you can.

While people anxiously wait for the slick in the Gulf of Mexico to wash up along the coast, globules of oil already are falling to the bottom of the sea, where they threaten virtually every link in the ocean food chain, from plankton to fish that are on dinner tables everywhere.

"The threat to the deep-sea habitat is already a done deal -- it is happening now," said Paul Montagna, a marine scientist at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi.

Hail-size gobs of oil the consistency of tar or asphalt will roll around the bottom, while other bits will get trapped hundreds of feet below the surface and move with the current, said Robert S. Carney, a Louisiana State University oceanographer.

Oil has been gushing into the Gulf of Mexico at a rate of at least 200,000 gallons a day since an offshore drilling rig exploded last month and killed 11 people. On Wednesday, workers loaded a 100-ton, concrete-and-steel box onto a boat and hope to lower it to the bottom of the sea by week's end to capture some of the oil.

Scientists say bacteria, plankton and other tiny, bottom-feeding creatures will consume oil, and will then be eaten by small fish, crabs and shrimp. They, in turn, will be eaten by bigger fish, such as red snapper, and marine mammals like dolphins. The petroleum substances that concentrate in the sea creatures could kill them or render them unsafe for eating, scientists said.

Scientists are watching to see whether the slick will hitch a ride to the East Coast by way of a powerful eddy known as the "loop current," which could send the spill around Florida and into the Atlantic. If that happens, the oil could foul beaches and kill marine life on the East Coast.

In South Carolina, no preparations were under way Wednesday to deal with the possibility of tar balls from the spill washing up on beaches, but federal and state agencies had begun to talk about it. Homeland Security keeps a contingency plan that gives the Coast Guard the lead role and provides for boom operations to corral the mess.

"So far it (pollution) doesn't seem to be a significant threat," said Priscilla Wendt, S.C. Department of Natural Resources environmental quality manager.

The plan pulls in assistance from a long list of groups that includes county emergency preparedness departments and environmental organizations such as the Center for Birds of Prey in Awendaw, Save the Wando and Concerned Citizens for the Ashley.