Below, in a world not so removed from that of humans, tiny snails, worms and crabs move among short, thumb-thick green shoots with fanning leaves and long, thin grasses that sway toward the sun from the muddy bay bottom.

Black-eyed juvenile shrimp and sleek baby fish flit along those grasses, eating algae and pouncing on worms, grubs and insects. Adult flounder and mullet drop in for occasional visits to graze the buffet of fish, grasses and creatures smaller than a pinky nail.

It is this place, the tireless and mysterious bottom of Alabama's bays, that scientists and conservationists this year are seeking to protect by closing large swaths to shrimp trawling.

Shrimp nets and the chains and weights that take them to the bottom, according to many scientists, scour bay and sea floors, devastating the delicate underwater environment, leaving in their wake plumes of sediment and a ruined, barren landscape similar to a forest that has been clear cut.

Such dramatic descriptions do not precisely apply to the shallow-lying grass beds of muddy, murky Mobile Bay, which are largely inaccessible to shrimp trawlers, according to local scientists and fisheries regulators. Still, a long-term break in trawling in Mobile Bay could have dramatic -- and beneficial -- effects all the same, they said.

Alabama's coast boasts one of the Gulf of Mexico's most important breeding grounds for shrimp and fish, according to marine scientists. Mobile Bay is the Gulf's largest open bay and the sixth largest drainage basin in the United States. At an average depth of 10 feet, it is also among the Gulf's shallowest bays.

Decades of environmental damage and habi tat loss in the bay have launched a debate this year about the area's 30-plus years of shrimp trawling, in which a small fleet of boats seasonally drags bottom areas, often repeatedly.

The big talk

Last month, the talk began. The Mobile Bay National Estuary Program -- a federal entity charged with improving the state's inlets and bays -- hosted the state's first meeting in seven years on closing areas to trawl nets.

The group brought together conservationists, fisheries managers and callous-handed fishermen to discuss what it would take to hammer out a plan each group could live with, said David Yeager, director of the estuary program. This month, Yeager informed the state policy-making Conservation Advisory Board of the ongoing no-trawl-zone discussions. The advisory board may choose to vote on the bay closure proposal at its final meeting this year, which will be set for May or June.

But the consensus Yeager hopes to deliver to state officials at that meeting seems far away. The talks have pitted those who favor a wide-ranging closure, generally conservationists and recreational fishermen, against shrimpers, who oppose creating any no-trawl areas whatsoever in state waters. The two sides remain divided, for the time being.

"I think it's a fairly clear case. The shrimpers would get more shrimp, the recreational fishermen would catch more fish, and the bay would be healthier," said Dan Dumont, director of the Alabama Forest Resource Center, a nonprofit land trust organization, in a recent telephone interview. Dumont said he has participated in the discussions as a conservationist.

"It is pretty clear," said Ernie Anderson, president of the Organized Seafood Association of Alabama, the group that has opposed no-trawl zones most passionately. "This looks like an underwater land-grab by the recreational fishermen."

No one knows exactly how many Alabama shrimpers use upper Mobile Bay yearly. That kind of monitoring isn't done, and state licenses are not divided up in a way that would separate bay shrimpers from Gulf shrimpers, said Chris Denson, a biologist with the Alabama Marine Resources Division. Currently, 2,540 people hold state shrimping licenses, 574 of them operating boats less than 30 feet in length.

Those smaller boats are likely to drag their nets in the bay at least part of the year, generally in the fall as white shrimp season opens, said Sonny Knowell, 64, a longtime bay shrimper. He said he's shrimped for decades in the upper bay.

"I don't get up in the shallows. My boat draws six feet of water, and I'll bog down if I get near them," Knowell said. A very few shrimpers do trawl over the seagrasses, not with bottom-dragging otter trawls but with butterfly nets that stay closer to the surface, he said.

"Most of us don't go up there anyway, so what are they wanting to protect?" Knowell said.

The science

At issue are the effects of trawling on three things in estuarine waters -- seagrass beds, finfish populations and the habitat of the insect-like creatures that burrow into the muddy bottom.

Mobile Register interviews with several Gulf-based marine science experts and a review of available scientific literature revealed no directed studies on these subjects in Mobile Bay.

"We're really light-years behind other states where this is concerned. Our understanding of Mobile Bay is really still in its infancy," said John Valentine, a University of South Alabama fisheries biologist. "We don't have the quality of funding or community involvement other states have."

Still, studies done in other states and anecdotal scientific evidence can fuel understanding of these issues in Mobile Bay, he said. And if the state does eventually close the upper bay to trawling, studies can be done that would catapult our understanding of the bay forward, he said.

Seagrass

Hugging the shallow waters where the sprawling, 185,000-acre Mobile and Tensaw River Delta gradually becomes Mobile Bay are large swaths of underwater plants -- an unseen forest floor that serves as both dormitory and nursery to young fish and shellfish.

In most places around the Gulf, seagrasses are dying. Mobile Bay is no exception, according to past surveys. In the past 50 years, sea grass losses have ranged from 50 to 100 percent in estuaries from Florida to Texas, according to various academic, state and federal studies.

A study of aerial photos taken of Mobile Bay from 1955 to 1979 showed a loss of 49 percent of seagrass beds. A new aerial survey of Alabama's grass beds now in draft form shows some 6,641 acres of the grass beds. A comparison of those photos, taken in 2002, with aerial studies done since the 1950s is now under way, said Yeager of the Mobile Bay National Estuary Program, which is paying for the studies.

"I remember back in the '40s and '50s, out there where Fairhope Pier is, you could wade out and there was a huge, thick seagrass area there," said John Borom, 62, a biologist and director of Faulkner State Community College. Those seagrasses vanished by the 1980s, he said.

The impact of trawling on seagrass loss in the bay is not easily quantifiable, Valentine and others said. Many other things have contributed to seagrass loss, including bulkheading, which wipes out seagrasses and their habitat directly, as well as polluted runoff from sewage plants, industry, upland pollution and fill dirt from local construction, Valentine said. Seagrass losses in faraway places like China and Australia have led some researchers to suspect a larger cause, like global warming.

Some conservationists and regulators feel that dragging nets may prevent seagrasses from growing in areas where they might otherwise. The nets scour the bottom, sending a plume of mud into the water that Florida researchers have found can stay suspended for eight hours.

That suspended dirt can choke out light for plants that already are on the threshold of the depth at which they can grow, said Paul Carlson, a researcher at the Florida Marine Research Institute. Resuspended sediments can settle on top of grasses, choking light further.

The Mobile River, which is part of a system that its origins in the Appalachians, tends to be very muddy. Mobile Bay is so murky that sunlight doesn't penetrate very deeply. Submerged plants grow only in very shallow water -- 3 or 4 feet deep at most, Valentine said.

Shrimpers maintain that seagrasses are growing in all the areas where they are able to grow.

"But it's possible that if we stop trawling in these areas, some seagrasses may come back," said Steve Heath, chief biologist for the marine resources division of the Alabama Department of Conservation and Natural Resources. "If this closure happens, we'll be monitoring for that."

Bycatch

South Carolina's sounds and bays were permanently closed by the state Legislature in 1986, said David Whitaker, director of the office of fisheries management at the South Carolina Department of Natural Resources. The closure was done largely for economic, not ecological, reasons, he said.

"A coalition of large shrimp boat captains and environmental folks got together," Whitaker said. "The big trawlers didn't want the small boats taking the shrimp first. They said the shrimp would be bigger."

In 1989, the department completed a two-year study of the closure's effect on shrimp and recreational finfish populations. The study concluded that the shrimp caught were indeed bigger, but roughly for every pound gained in shrimp size there was a loss of a pound of juvenile shrimp to natural predators.

"If the shrimpers didn't get them, the predators did," Whitaker said. The overall catch was more valuable, as the big boat captains had predicted, Whitaker said.

Local shrimpers said a political division between small and big shrimpers was unlikely in Alabama.

"I'd have everything to gain by letting them close the upper part of the bay," said Anderson of the Organized Seafood Association, who owns Graham Shrimp Co., a Bayou La Batre shrimp company with four large, Gulf boats and an unloading dock.

"But we're all related around here," Anderson said with a laugh. "Really, we stick together."

The South Carolina study had another interesting outcome, Whitaker said. Recreational fishermen have long contended that shrimpers' nets snatch popular sports fish from estuaries when they are young, killing them in their nets or suffocating them on the culling table.

"There was no significant difference between recreational catch before and after the closure," Whitaker said. But unpopular "trash" fish such as star drum, blackcheek tonguefish and sea catfish, grew in numbers, he said.

It should be noted that South Carolina's bays don't have seagrass beds, like those in Mobile Bay, he said. A long-term study of the effect of a trawling closure on fish and shellfish in an estuary like Mobile Bay could not be located.

Critters

The vast majority of Mobile Bay's 200,000-acre bed is mud. Where it dips past four feet, down to 10 and 15 feet in depth, very little or no sunlight hits the bottom, Valentine said. Vegetation is impossible there, but that doesn't mean the floor is dead.

It is positively alive with thousands of small, crawling, burrowing creatures. These creatures are necessary to the normal functioning of the nutrient exchange system, according to research papers. The organisms consume soil and other matter on the bottom, convert it to a different form as they digest it, which in turn can be digested by the fish who eat the bottom-dwellers.

When shrimp trawls pass over these muddy bottom areas, they flatten out and crush wide swaths of soil, closing up or collapsing the delicate burrows of these creatures, according to a 2000 University of Maine study. Many of them are killed.

In oceans, the effects of this over time can be dramatic, according to the study -- starving out creatures like crabs and giving an advantage to "suspension feeders" like mollusks, plankton and jellyfish. Local scientists contacted said they didn't know what the long-term effects would be on an ecosystem like Mobile Bay's.