Correction: An earlier version of this article incorrectly said that the oyster population in Maryland is 36,000. It should have said that the area of habitat suitable for oysters in the state is 36,000 acres. The article also said that the U.S. Army Corps of Engineers is preparing a Native Oyster Restoration Master Plan for the Chesapeake Bay that aims to expand the oyster habitat in both Maryland and Virginia from 450 acres to tens of thousands of acres by 2032. In fact, it aims to expand oyster sanctuaries in the two states. This version has been corrected.

An oyster from Massachusetts is shucked at the Old Ebbitt Grill in Washington. With the Chesapeake Bay oyster population depleted, the restaurant turns elsewhere for its oysters. (SUSAN BIDDLE/FOR THE WASHINGTON POST)

For Chesapeake Bay oysters, the urge to mess around starts with a warm and relaxing bath.

Researchers at the University of Maryland Center for Environmental Science know this because they stand over climate-controlled vats of water and watch. It’s not the mating rituals of mollusks that fascinate them. They are monitoring a key first step in an expanding government effort to save the endangered bay oyster — and with it, the sickly bay itself.

“We believe the Chesapeake Bay cannot be restored without the restoration of oysters,” said Tom O’Connell, director of fisheries services for the Maryland Department of Natural Resources. He explained that oysters play a major role in filtering pollution. “Oysters alone can’t improve water quality, but they are an essential ingredient.”

The bay is the nation’s largest estuary, the lifeblood of Maryland and Virginia. It is a precious resource that shapes cultural identities — such as that of the now-threatened waterman — and the region’s way of life.

Maryland recently embarked on a new effort to super-size the oyster population, encouraging them to procreate like crazy by expanding their habitat, increasing aquaculture farming and setting aside larger river sanctuaries to protect them from harvesters.

O’Connell said the state is determined to improve on a previous effort. After spending at least $50 million in state and federal funds since 1994, according to O’Connell, Maryland has managed only to maintain a very small area of habitat suitable for oysters — 36,000 acres, a 70 percent drop from what it was 30 years ago. That failure dampens optimism that the historic oyster population can ever be restored.

The drive to go bigger on oyster restoration goes beyond Maryland’s program, which began with the opening of the harvest season in September. In the fall, the Army Corps of Engineers is expected to announce its Native Oyster Restoration Master Plan for the bay.

The master plan aims to expand oyster sanctuaries in both Maryland and Virginia from 450 acres to tens of thousands of acres by 2032, at a cost of $66 million, mostly federal dollars, according to the corps.

Where the magic happens

It all starts with the oyster and its offspring. Scientists who encourage them to get busy and prosper at the University of Maryland’s Horn Point Laboratory are trying to perfect 100-year-old aquaculture science. May to September is the optimum time frame to seed oyster reefs.

In that soothing warm water, clam-tight adult males loosen up and release sperm that floats on a current. The females respond by tossing out microscopic eggs by the tens of millions. Last week, Don “Mutt” Meritt, the hatchery’s director, scooped some up after they were fertilized.

Meritt oversees the development of a billion eggs in eight 10,000 gallon tanks at the hatchery. He babies them with a brew of homegrown algae until they grow into “spat” that are ready to attach to a hard surface. Meritt makes sure the surface is a shell — the building block of the reefs that the baby oysters need to survive and thrive as adults.

Oysters purify bay waters by eating algae. The plant is a natural part of the bay, but too much of it blocks sunlight, sucks up oxygen and causes fish kills, and produces toxins that stink to high heaven.

For centuries, oysters have chomped algae and spit it out in chunks that fall harmlessly to the bay floor. On top of that, their reefs invite dinner guests — sponges, barnacles and mussels — that also scarf algae. An adult oyster can filter as much as 50 gallons of water per day, according to the Chesapeake Bay Foundation.

Many of the shells on which workers pour the spat are collected from restaurants with raw-oyster bars in the District, Virginia and Maryland by the Oyster Recovery Partnership.

Shell collecting

The partnership turned to the restaurants because of the dwindling number of shells in the wild. At the restaurants, kitchen staff traditionally tossed shells in the trash after diners slurped oysters.

Old Ebbitt Grill in the District, where 700,000 mollusks were served last year, was one of the first places the partnership visited.

“It was a no-brainer for us,” said Christian Guidi, the restaurant’s general manager. “It was an opportunity for us to assist with the restoration of what used to be a great place for oysters.”

Bay oysters were once so plentiful in the Chesapeake that their reefs — a mountain of shells — caused shipwrecks around the time Jamestown was founded. Now they are so depleted from diseases caused by urban and farm waste that Old Ebbitt turns to Massachusetts, Rhode Island and British Columbia for its oysters.

Under the partnership, the restaurants instruct kitchen staff to save the top shell of each oyster after cracking it off to serve, and to save the bottom shell when plates are retrieved.

The filled buckets are taken downstairs and poured into bigger ones that are picked up by a truck twice a week. Last year, more than 40 restaurants participated. This year, there are more than 60, including the McCormick & Schmick’s seafood restaurant in Bethesda and Hank’s Oyster Bar in Alexandria, said Stephan Abel, the partnership’s executive director.

“Imagine if instead of a few thousand acres of oyster beds, we had hundreds of thousands like we did 400 years ago,” said Mark Bryer, director of the Chesapeake Bay program for the Nature Conservancy, one of several nonprofit partners in the restoration effort.

Bryer envisions underwater mountains of oyster shells peaking and dipping like the rails of a roller coaster.

“This is our great coral reef,” he said. “This is our awesome habitat.”

But it might be a pipe dream. Restoration of the oyster population that existed at Jamestown is hardly likely, Bryer said.

The partnership of environmental groups that includes the Nature Conservancy and the Chesapeake Bay Foundation are hard-pressed to find enough shells to seed the spat at the lab, let alone rebuild enormous shell habitats in the rivers.

And there are other drawbacks. After the spat are poured onto shells at the lab, they are whisked to giant oyster reefs in rivers such as the Chester, Choptank, Patuxent and Magothy, where they are ejected in the hope they will grow to adulthood and start the mating ritual all over again.

But only a fraction of the spat survive. Some die when the side of the shell they are stuck to smacks the ground.

“I call it the luck of the fall,” Meritt said.

Bottom-feeding fish gobble their fair share.

Governments will keep seeding tens of millions of spat in rivers because oysters are so critical to the bay’s survival, said Claire O’Neil, project manager for the Army Corps’ Chesapeake Bay oyster restoration project in Maryland.

“I think most environmentalists agree that the oyster is simply the keystone species for the bay,” she said.