The swath of Atlantic Ocean the Obama administration may open to oil and gas exploration is an ecologically diverse network of soft-bottom shelves and rocky canyons that includes some of most dynamic and mysterious marine systems on Earth.

The 500-mile-long (805-kilometer) region stretching from Virginia to Georgia hosts 700 fish species, five types of sea turtles, migrating humpbacks, and endangered fin whales and right whales with sensitive acoustic systems. Seabirds by the millions float along the Gulf Stream as it carries warm water and nutrients north.

Beyond the continental shelf, where the seafloor slopes down into the abyss, the bottom of the ocean is cut by canyons deeper than the Grand Canyon that are visited by tilefish and home to spindly-legged crabs. Newly discovered deep-sea coral gardens host so many bizarre creatures that one scientist said it's like "Dr. Seuss went crazy down there."

Yet very little is known about how much oil and gas there is—or just how big a threat extracting the resources might pose.

"It's a big open question at this point," said Peter Auster, of the University of Connecticut's Northeast Underwater Research Technology and Education Center. "Many of these things go on with nothing bad happening most of the time. But with these sorts of things, we have to always assume there's going to be an accident at some point. And that can have impacts that last years or even decades."

Any move to drill off the Atlantic coast is years away, and may never actually happen. The administration's plan merely starts a long process of public and environmental review.

The known quantities of oil and gas are tiny, especially when compared to the Gulf of Mexico or Alaska, and energy prices are in the tank. And though many people, including several southern governors, have expressed enthusiasm for offshore exploration, there is also great opposition.

Marine researchers who understand the Atlantic's particular challenges say there are many hidden dangers to consider.

"It's possible the risks could be small if everything is done just right," said Larry Cahoon, a biological oceanographer at the University of North Carolina, Wilmington. "But that's a really, really, really big if."

View Images Conger eels are found among the deep-sea corals of the Atlantic Ocean. Photograph by age fotostock, Alamy

Lessons From Last Time

Few know the stakes as well as Cahoon, who sat on an advisory council that examined the potential for offshore oil development in the Southeast in the 1980s.

At the time, Mobil Oil sought to drill for oil 35 miles (56 kilometers) off Cape Hatteras, North Carolina. Everyone assumed little of ecological consequence lived there and that any accident or spill would send contaminants out to sea.

But the common seaweed sargassum regularly washes ashore from the open ocean, and Cahoon and his colleagues determined the same currents could drive any spill toward land.

"We found out the prevailing currents meant that about 30 percent of any oil in a spill would wash up on North Carolina beaches," Cahoon recalled.

It also turned out that the area in question was a biological hot spot, not a desert—as local fishers well knew.

"It's where the tuna guys went, where a lot of fish migrated, and where almost all the seabird populations in the North Atlantic meet to mate and feed," Cahoon said.

The grassroots outrage fueled by the 1989 Exxon Valdez oil spill in Alaska eventually led the government to pull the plug on exploration off North Carolina. Two decades later, the 2010 BP oil spill in the Gulf of Mexico likewise prompted the Obama administration to shelve its earlier offshore oil development plan.

View Images The deep-sea coral gardens found off the Atlantic are home to an unusual variety of sea life, including Lophelia pertusa (above). Photograph by Lophelia II 2009: Deepwater Coral Expedition: Reefs, Rigs, and Wrecks, NOAA Ocean Explorer

The Stakes Haven't Changed

In its latest plan, the White House is proposing to sell drilling leases no closer than 50 miles (80 kilometers) from shore, which would exclude the region once targeted by Mobil.

But scientists say many of the same ecological issues would recur.

The continental shelf, which stretches far out to sea off New England, ends much closer to shore in parts of the South. That brings colliding currents and a mixing zone of deep and shallow water closer to where exploration might occur.

"What we've found is, that is one of the most dynamic regions in the sea," said Steve W. Ross, a research professor at UNC-Wilmington who has studied the region's submarine canyons and deep-sea corals. "There are a lot of places where you just wouldn't want to have an accident."

Even out here, everything is connected. Upwelling of cold water brings nutrients toward the surface, and they then get pushed toward shore. Sunlight triggers plankton blooms that spread back out to sea, where they feed other fish and marine species.

Out past the shelf off Virginia, deep canyons serve as funnels, trapping organic matter that supports an array of life scientists have started to catalog only in the past few years. That includes large numbers of three-foot-long (one-meter) cod-like cusk, which have largely disappeared from areas closer to shore.

To the south, mounds of deep-sea coral rise as much 650 feet (200 meters) high, providing homes for black-bellied rosefish and conger eels.

"In a spill, every part of the ecosystem is potentially at risk—the bottom, the upper water column, the surface, the shore," Ross said. "There are not a lot of places where you could say, 'We could afford to write that off.'"