Each year, a plane takes a long, 12,000-foot-high journey across the Chesapeake and the Atlantic coastal bays of Maryland and Virginia, taking pictures all along the way.

That yields an annual crop of photos that scientists at the Virginia Institute of Marine Science use to determine where beds of submerged aquatic vegetation are expanding - and disappearing. But in the past year, the photos raised an alarm.

It the midst of grass beds in Chincoteague Bay, on the seaside of Virginia's Eastern Shore, large circles of grasses had completely vanished.

"It looked like alien landing patterns," said Mike Barnette, of the Virginia Marine Resources Commission.

In Maryland's part of the bay, meanwhile, the high-altitude photos showed cleared paths winding through grass beds which one scientist described as "snake trails."

In both instances, the impact on SAV beds was blamed on clam-harvesting equipment.

Responding to concerns, the VMRC in December set the Chincoteague Bay grass beds aside as a sanctuary. The action immediately closed the beds to clamming; final details of the sanctuary are to be worked out by the commission's January meeting.

"It's going to be a pretty good chunk of real estate," Barnette said. "The industry recognized it as an important habitat. They understand that SAV is critical to the reestablishment of the bay scallop industry."

Meanwhile, the Maryland Department of Natural Resources has established a special workgroup of watermen, environmentalists and others to examine what - if anything - should be done about the issue. A recommendation is expected by March, but the issue is controversial.

Those agency activities, at least in part, reflect increased emphasis placed on protecting SAV beds as their importance has been recognized in documents such as the Bay Program's Blue Crab Fishery Management Plan.

"I think that [the blue crab plan] was probably a very important element," said Bob Orth, a scientist at the Virginia Institute of Marine Science.

"We've been able to show that this is an important - if not the most important - habitat for the blue crab in the Bay as a nursery." Barnette agreed: "It's there in black and white that we should protect this, and the reasons why it should be protected."

At the same time, it raises questions of how far government agencies should go to protect grass beds - and the potential consequences of such actions.

In both Maryland and Virginia, the state must approve plans for many structural activities that affect SAV beds, such as channel dredging, dumping dredged material on beds, pier construction or marina development.

Policies tend to prohibit or discourage such direct impacts, though questions remain about how much protection should be given to "potential habitat" - areas up to 6 feet deep that could someday hold grasses if the water ever gets clean enough. "If it's an existing grass bed, the issue is pretty clear," Barnette said. "But if there's just sandy bottom, even though it's only 2 feet of water, it's hard to say."

Fishing meanwhile, is regulated differently from structural changes to grass beds. And the debate going on in Maryland could foreshadow future disputes with fishermen - and other user groups - over potential impacts on SAV of everything from fishing gear to recreational boat props.

The clamming issues arose when the annual SAV aerial survey showed that hundreds of acres of grasses, primarily in the coastal bays and to a lesser extent in the Chesapeake, had been heavily scarred in 1997.

"The change in intensity and the extent of the scarring from '96 to ' 97 is mind-boggling," Orth said. "The seriousness of this is pretty high."

Larry Simns, president of the Maryland Waterman's Association, disputed that there has been a major shift to clamming in grass beds - or that clamming causes any long-term damage. He said grasses were coming back in some previously barren areas that had been clammed for years.

"If clamming were so destructive, then there wouldn't be any grass in the clamming area," Simns said. "Clamming is so small an environmental factor compared to all the other factors that I don't think the clamming has any impact."

In fact, the total number of acres affected is in the hundreds of acres. By contrast, the amount of beds in the Bay routinely fluctuates by thousands of acres every year, primarily because of water quality issues.

But Orth and some other scientists worry that the scars done to the bottom by hydraulic dredge equipment - which sends jets of water into the sediment to unearth clams - could prevent recovery for years.

He and others question whether any preventable losses should be allowed at a time when tens of thousands of dollars per acre is being spent to restore grass beds. If grasses had to be replanted in areas damaged by clamming, Orth said, it would cost millions of dollars.

Bill Goldsborough, a fisheries scientist with the Chesapeake Bay Foundation, said no one would be allowed to destroy hundreds of acres of wetlands without - at a minimum - being required to construct new wetlands to offset the loss.

"I think the same standard ought to apply to SAV, which has every bit as much - if not more - value to the Bay," Goldsborough said.

"What we're trying to do here is establish an ethic for the Bay," Goldsborough said. "Not just with this issue, but in general. We are trying to get everyone to do their part. Everybody whose activity is adversely affecting the Bay, we're trying to get them to change that activity."

But in Maryland, Mike Naylor, a member of the DNR team working with the special clamming workgroup, said the department's goal is to let interested parties reach a consensus over what, if anything, should be done.

A regulation that makes SAV untouchable is not realistic, Naylor said. "We know that recreational boating has an impact on SAV, we've known that for a long time, but you can still buy a boat," he said. "And no one is going to say we're not going to allow anyone to boat on the Bay because some SAV is destroyed."

Because hydraulic dredging has been conducted on the Bay for decades without visible impacts, Naylor said it was possible that the 1997 damage was a one-time event. "No one wants to make a whole bunch of regulations for something that was only a problem one summer," he said.

But if the state moves toward becoming more strict about clamming and other activities in grass beds, Naylor said it will raise a number of practical issues.

"Let's say we want to protect all SAV beds," he said. "How do you enforce that? What is an SAV bed? Is one plant every six meters an SAV bed? Or is it two plants every six meters? Or one plant every every 20 meters? If you are going to try to prosecute people for harvesting in an SAV bed, you had better know what an SAV bed is."

Orth, saying the grass beds were valuable for more species than just clams, said the state needed to act soon to define - and protect - beds from the clamming impact. He estimated more than 1,200 acres of grasses in Maryland's coastal bays had some degree of scarring, a 10-fold increase from 1996. "The density of these scars are horrible," Orth said. "They're destroying more area than [were destroyed] in all of Virginia's coastal bays."

But as oysters and other Bay species have declined, clamming has become a more important fishery for many watermen, who say they are being singled out for blame.

"The biggest problem is the nitrogen, the phosphorus and all the nutrients going into the water that smother out the sunlight," Simns said. "We're not saying that we don't want to protect the grass. We're saying don't put us out of business and then still let the grasses die because of all these other things. That's what is happening here."