By Matthew A. Ward
NORFOLK, Va (Reuters) - After 10 years of cultivating oysters in the waters off his backyard dock, Kendall Osborne has developed something of a salt thumb.
He began gardening oysters as a way of bonding with his two daughters and, like hundreds of other Virginians, to help bring the ailing Chesapeake Bay back to life and rid it of dead zones where no sea creatures can survive.
"It's fun to see them grow," said Osborne, whose Norfolk, Virginia, home sits on the shore of the Lafayette River. "When we get them they're very small, about half the size of your pinky fingernail. A year later, they're 2, 3 and occasionally even 4 inches long."
Scientists estimate Chesapeake Bay's oyster population has plummeted to less than 5 percent of levels before European settlement, and oyster gardeners hope their effort to replenish the mollusks will help improve the environment in the bay.
Oysters form large reefs that provide a habitat for marine plants and animals. They feed by filtering microscopic plants from the water, improving water quality, and as adults can filter up to 50 gallons (190 liters) of water a day in optimum conditions.
"If you look at the time of first contact, when the original oyster population had been in place for hundreds of thousands of years, they were able to filter the entire Chesapeake Bay, which is a huge volume of water, in about three or four days," said Tanner Council, a coordinator for the Chesapeake Bay Foundation, which runs an oyster gardening program in Virginia.
"Now it takes the better part of a year."
Volunteer gardeners, of which there are an estimated 300 in Virginia, plant their baby oysters in the late summer and early fall. A year later the gardeners voyage out to sanctuary reefs where the mollusks are deposited.
Council's foundation, which works to better the nation's largest estuary through community involvement and education, also runs a program in Maryland. Other organizations such as the Tidewater Oyster Gardeners Association operate similar programs.
Federal and state governments have spent more than $5 billion trying to clean up the bay, which has a watershed of more than 64,000 square miles (166,000 sq km) and is home to commercial quantities of fish and crabs, as well as oysters.
Pollutants such as nitrogen and phosphorus flow into the bay from treated sewage, fertilizer and animal manure, leading to unnatural algae blooms and using up oxygen needed by other inhabitants.
As a result, the bay and its tidal waters are stricken by dead zones where sea creatures cannot survive.
In May 2009, President Barack Obama issued an executive order to restore the bay after it continued to fail the "fishable and swimmable" goals of the Clean Water Act.
In response, the Environmental Protection Agency last year published maximum daily pollution guidelines with accountability measures for the six bay states and the District of Columbia.
Those governments are developing Watershed Implementation Plans, which aim to install by 2025 control measures to fully restore the bay and its tidal rivers.
Various other government arms are working toward a solution, including the Department of Agriculture, which in mid-August pledged $848,424 toward reducing the use of manure -- a major phosphorus generator -- as fertilizer.
The Chesapeake Bay Foundation says volunteer oyster gardening efforts are a key part of the solution.
"There's tipping points at which populations can crash," Council said. "When all the dots connect you can have a bloom in the oyster population, which is the kind of thing that we're really looking for."
(Editing by Colleen Jenkins and Cynthia Johnston and Greg McCune)