The reproductive cycle of the Chesapeake Bay's blue crabs has all the elements of a good romantic epic: a sweeping scale, a cast of thousands and protagonists caught up in forces beyond their control.

It starts with fertilized females migrating to the lower bay to spawn, sometimes traveling dozens of miles underwater. Then, after their eggs have hatched, the tiny crab larvae are swept into the Atlantic Ocean. These microscopic creatures must rely on the tides to return them to the bay.

For years, it was thought impossible to build a hatchery for blue crabs: Who could re-create this saga in a tank?

"We were told when we started, 'Don't even touch it; it's not going to work,' " said Yonathan Zohar, a professor at the University of Maryland Biotechnology Institute.

But, after much experimentation, it has worked.

Zohar and his team have built the first hatchery for blue crabs, raising them from eggs to nickel-size juveniles in a laboratory at Baltimore's Inner Harbor.

This is the third year they have released thousands of hatchery-raised crabs in the wild, after launching the program in the summer of 2000.

Scientists say the hatchery marks a significant achievement, even if it never produces enough crabs to restore the bay's flagging population. At the least, they say, this work has provided valuable insights into the crab's once-mysterious life cycle.

"This was one stone that we couldn't leave unturned," Zohar said.

The blue crab is one of the most important creatures in the bay, both economically and as a symbol of Chesapeake culture. Watermen catch millions of pounds of crabs every year, pumping tens of millions of dollars into the economy in Maryland and Virginia.

But, for all the creatures' prominence, many basic details about blue crabs had remained poorly understood: How long do they live? How many times can a female spawn?

Part of the problem was that crabs frequently shed their shells, frustrating efforts to tag them or determine their age by looking for growth rings.

In short, "nobody knows anything about crabs," said Larry Simns, president of the Maryland Watermen's Association.

In this environment, disagreements have persisted for years between the scientists who study the crabs and the watermen who catch them. Their division is this fundamental: They even disagree about whether the crab population is growing or declining.

Scientists cite surveys estimating that the number of crabs in the bay dropped to about 200 million last year, from an estimated 870 million in 1993.

But watermen say they are catching more crabs this year. So many more, in fact, that Simns said they are having trouble selling them.

"The crab doesn't need bringing back," Simns said, "because we've got plenty of them."

Into this information enigma stepped Zohar and his team. They have been praised by both scientists and watermen for discovering details about crab biology.

"What we are getting are a lot of the basic life-history characteristics of the crab that we've never been able to measure," said Lynn Fegley, blue crab program manager for the Maryland Department of Natural Resources. "Their work up there is just invaluable."

Zohar directs the University of Maryland's Center of Marine Biotechnology, which was established in 1985. He runs a $2 million laboratory that is funded by the federal and state governments and by more than $400,000 from Baltimore's Phillips Seafood.

The building, on a pier behind the Inner Harbor's Hard Rock Cafe, also holds tanks where scientists are experimenting with sturgeons, rockfish and a fish called sea bream, but its marquee residents are the blue crabs.

The hatchery's work begins with "sooks," or fertilized female crabs, that are caught by watermen. The scientists control the crabs' spawning by manipulating the light, water temperature and salinity in the tanks.

On one recent day, one tank held female crabs that were in winter mode, the water kept cold and the light limited to a few hours each day.

"When we want them to spawn, we'll move them into springtime conditions," Zohar said. That means warmer water, more hours of light and higher salinity to mimic their trip to the saltier waters of the lower bay.

The eggs released by these females will hatch into microscopic larvae. At the hatchery, these are the most demanding of infants. Zohar and his team have to feed them a constantly shifting diet of tiny food to re-create their life in the wild.

For instance, in one tank of tiny 3-day-old crabs, the scientists added microscopic animals called rotifers for the crabs to feed on, plus even smaller bits of algae for the rotifers to eat. The algae and the rotifers also are raised in the laboratory, along with the brine shrimp -- better known as sea monkeys -- that the crabs eat at a later stage of development.

As the hatchlings change from larvae and begin to resemble adult crabs, Zohar's team faces another problem: cannibalism. When small crabs shed their shell, they are as tempting to their siblings as soft-shell crabs are to humans.

To combat cannibalism, the scientists have given the crabs extra food, tried to separate larger and smaller ones, and added plastic netting in the tanks to give molting crabs a place to hide.

After about 60 days in the hatchery, the crabs are ready to be released into the wild. Of the 1 million or 2 million eggs released by one female crab, only 30 or 40 percent usually survive this long -- a rate, however, that is much higher than in the wild.

By taking the crabs through this process, Zohar said, his team has learned "all kinds of cool things." Among them: Crabs can grow to sexual maturity in a few months -- not years, as had previously been thought.

Also, Zohar said, the team discovered that female crabs can produce five batches of eggs. He said watermen had previously thought that the crabs spawned once and then died.

Simns, the watermen's association president, said the watermen had actually known about that ability all along.

"It wasn't any surprise to us," he said. "But it was a surprise to a whole lot of people" in the scientific community, he said.

One of the release sites for the hatchery's crabs is in Virginia's York River. The other is in the Rhode River at the Smithsonian Environmental Research Center near Edgewater. In this year's first batch, a total of about 26,000 juvenile crabs were released at the two sites.

On one recent day in Edgewater, college-age volunteers were tagging the little crabs before they were released. Each crab was injected -- in what one scientist unceremoniously called the "butt muscle" -- with a tiny piece of magnetic wire and a bit of bright orange dye.

Those were designed to allow scientists to identify hatchery-raised crabs caught in the wild. The tags are injected into the crab's muscle so that they are not lost when it loses its shell. Scientists said the tags are too small to pose any harm to humans who might consume the crabs.

After being tagged, the crabs were put in a cooler, then carried out in a boat into a shallow, muddy cove.

"Just start putting them in their new happy home," said Eric Johnson, a postdoctoral student, as the crabs were dumped in.

It's not always so happy. The scientists estimated that 20 to 30 percent of the crabs they released in 2002 reached sexual maturity. But in 2003, a year of heavy pollution in the bay, the number dropped to between 5 and 7 percent, said Anson "Tuck" Hines of the Smithsonian.

It's unclear whether enough crabs will be released here to affect the bay's population. Donald F. Boesch, president of the University of Maryland's Center for Environmental Science (which operates the Chesapeake Biological Laboratory at Solomons), said that so many crabs are eaten -- by fish, other crabs or humans -- that it would require an impossibly large number of hatchlings to produce significant numbers of adult crabs.

"You can't compete effectively with the scale of Mother Nature," Boesch said.

But the hatchery scientists still have not conceded. Trying to improve their crabs' chance of survival, they are considering adding sand to the bottom of the tanks so the crabs will know to bury themselves to hide from predators in the wild.

The scientists' dream is to turn over the hatchery technology to watermen and produce the crabs in larger and larger numbers. To that end, they plan to open a larger facility this year at an old oyster hatchery in southern Calvert County near Solomons Island.

"Tank space is the limit. Size is the limit," Zohar said, referring to the capacity of his current lab. "Otherwise, the sky is the limit."

Eggs protrude from a blue crab at the Center of Marine Biotechnology, where thousands of crabs have been raised. The project has answered old questions about their life cycle.University of Maryland scientist Yonathan Zohar, above, helped build the first hatchery for blue crabs. At right, a baby crab gets injected with a tiny coded wire tag at a release site at the Smithsonian Environmental Research Center so it can be identified later.