Copied from the Times Dispatch

Loss of eelgrass threatens crabs

Chesapeake Bay vegetation that supports marine life is dying off

Sunday, Mar 23, 2008 - 12:08 AM

By LAWRENCE LATANE III

TIMES-DISPATCH STAFF WRITER

GLOUCESTER POINT -- Summer fun used to mean soft crabs and jimmies for Tom Powers, who merely had to wade into the Chesapeake Bay to catch his fill.

But that ended in 2005 when the 30-acre eelgrass bed he crabbed in disappeared.

"It died and it still hasn't come back," the Poquoson resident said.

That bed at Hunt's Point and thousands of other acres of eelgrass vanished when water temperatures climbed beyond normal in the lower Chesapeake Bay. Temperatures spiked temporarily between 2.5 and 3 degrees above normal during the summer of 2005.

Now, scientists at Virginia Institute of Marine Science are fearing more die-offs.

Years of research have proved that once eelgrass beds are gone, they don't come back, said Ken Moore, who has written studies on the stresses confronting eelgrass beds in the Chesapeake.

The underwater plant sends ribbonlike leaves sprouting from the bottom. They form dense green thickets of vegetation in the shallows that harbor a bounty of marine life.

Few species have as great a stake in eelgrass as the blue crab. The crab supports a multimillion-dollar commercial fishing industry, which is in trouble because of sharp declines in the crab population. Eelgrass beds provide welcome shelter for blue crabs shortly after they hatch in the Atlantic Ocean off the Virginia Capes.

"They have a chemical sensitivity" that allows them to detect the beds and hide from predators there once they enter the bay, VIMS scientist Jacques van Montfrans said. "We typically find 10 to 100 times more crabs in eelgrass than unvegetated sites."

When they can't find eelgrass, the baby crabs swim to the marshy fringes of the bay's tributary creeks and rivers, said Rom Lipcius, another VIMS scientist. But those bare mud bottoms are like a lion's den of hungry striped bass, croaker and bigger blue crabs.

Eelgrass acreage in the bay has dropped by more than half since its high of about 30,000 acres in the mid-1990s, according to a VIMS survey. About 13,500 acres were found in 2006.

Thousands more acres grew in the saltiest waters of the bay before June 1972, when Tropical Storm Agnes uprooted eelgrass colonies, smothered them with sediment and clouded the water with debris and pollution. Eelgrass died because sunlight couldn't penetrate the water.

As Moore's research found, the grass has never returned in Maryland, where Agnes hit hardest, probably because pollution limited the grasses' ability to survive, he said.

Intense efforts to replant eelgrass seedings and scatter eelgrass seed in Maryland waters have failed.

"I gave up trying to plant it," said Court Stevenson, a professor at the University of Maryland's Horn Point Laboratory on the Eastern Shore. "I'm not terribly optimistic about eelgrasses' future in Maryland."

Now a new threat is emerging in the lower bay with a rise in water temperature and a decline in water clarity, Robert J. Orth, a biologist at VIMS said.

"The bay's warming up. Eelgrass is a cool-water species and we're close to the southern limit of its range," he said.

Secchi disk readings, made by measuring the depth at which a white disk disappears when lowered into the water, show a gradual decline in water clarity in the bay's mainstem near the Maryland-Virginia line, said Mark Trice, who oversees water-quality data for Maryland.

Figures he supplied show average visibility readings from May through July last year were 1 meter -- about 39 inches -- or a half-meter less than the previous 20-year average.

Water pollution -- in the bay's case, nutrients from fertilizer run-off, septic-tank seepage and sewage-plant discharges -- feeds microscopic algae and bacteria that make the water less transparent.

As water temperatures rise, the eelgrass's metabolism speeds up, demanding the plant to produce more food through photosynthesis. Such a double-whammy is leaving eelgrass stressed in the lower bay, which scientists once considered a haven for the aquatic plant, Orth said.

Like his Maryland counterparts, Orth has ceased attempts to replant eelgrass beds, which also disappeared from the Virginia tributaries after Agnes.

On the other hand, he has had tremendous success on the seaside bays along Virginia's Eastern Shore.

A planting of eelgrass shoots about 10 years ago has regenerated 750 acres in South Bay. The difference between that coastal inlet and the Chesapeake is that it is open to cooler, pollution-free water from the Atlantic.

"What we're seeing is nature taking over," he said.