The Bay's underwater grass beds surged 12 percent last year to the second highest level observed in recent decades.

Overall, the annual survey mapped 85,899 acres, up from the 76,860 acres mapped in 2008. Still, acreage was less than halfway to the Baywide goal of 185,000 acres. The goal is based on the amount of grasses observed around the Bay in the past.

Scientists cautioned that much of the increase was driven by a large proliferation of widgeon grass in the mid-Bay.

Widgeon grass is notorious for expanding rapidly when conditions are good, then disappearing just as rapidly when water quality worsens, contributing to the often wide fluctuations in Bay grass acreage.

"It shows up and disappears. That is the nature of that beast." said Bob Orth, a scientist with the Virginia Institute of Marine Science, who oversees the annual survey.

Widgeon grass drove huge increases in areas such as the mouth of the Choptank River, Eastern Bay and the Honga River in the mid-Bay. Still, many of beds in those areas were much smaller than what was present just a decade ago: Eastern Bay roughly doubled its acreage, to almost 400 acres, from a year ago. But little more than a decade ago, it had about 5,000 acres, noted Lee Karrh, of the Maryland Department of Natural Resources and chair of the Bay Program's SAV Workgroup.

"It is good news that some of the grass came back in 2009, but the bad news is it is nowhere near what it was," Karrh said.

Still, he and others said there was plenty of good news in the numbers. Many grass beds, including the 12.4-square-mile bed in Susquehanna Flats-the largest expanse in the Bay-became more densely vegetated, something that can aid long-term stability.

Also, eelgrass-which suffered a major die-off in 2005 because of unusually warm water temperatures-continued to bounce back, although it has still not attained its pre-2005 levels.

The expansion of Susquehanna Flats and nearby Elk River appears to have halted, but scientists say that's mainly because the further expansion of those beds is limited by deep water, where water clarity is poorer. This still is the biggest success story in the Bay-a little more than a decade ago, those areas were sparsely covered.

"That continues to be the good news story," Orth said. "But I don't think we are going to see the big changes we've had in the past just because there is no more area outside of the deep water."

The annual aerial survey is a closely watched indicator of the Bay's health. Underwater grasses-more formally called submerged aquatic vegetation or SAV-require clear water to absorb the sunlight they need to survive, so they are very susceptible to nutrient pollution, which spurs algae blooms and sediment runoff, which cloud the water. They also provide some of the most important habitat in the Chesapeake, providing shelter for juvenile crabs and small fish, and food for waterfowl.

The survey found that beds increased in all geographic zones in the Bay-upper, middle and lower-for only the second time since 2001.

  • The upper Bay, from the Bay Bridge north, had 23,598 acres, a 3 percent increase from 2008. Beds in the upper Bay have almost reached the region's goal of 23,630 acres.
  • The middle Bay, which stretches south from the Bay Bridge to the Potomac River and Pocomoke Sound, had 39,604 acres, a 15 percent increase from 2008, but still well short of the 115,229-acre goal for that region.
  • The lower Bay, which is south of the Potomac-Pocomoke line, had 22,697 acres, a 17 percent increase from 2008. That was about half of the 46,030-acre goal for that region.

But those trends can be reversed just as quickly A series of dry years capped by drought conditions in 2002 drove an upward grass trend that reached 89,659 acres-the most observed since annual surveys began in the early 1980s. But heavy rains the next year washed away 30 percent of that acreage.