BALTIMORE (Map, News) - Underwater grasses in the Chesapeake Bay increased 10 percent last year but fell far short from the target, an annual aerial survey released Monday found.

The grasses — a major indicator of the overall health of the Bay — covered about 65,000 acres of the Bay and its rivers in 2007, which is 35 percent of the goal of 185,000 acres by 2010, according to the Chesapeake Bay Program, a regional partnership coordinating Bay restoration efforts.

“As the Bay grasses go, so does the Bay itself,” said Lee Karrh, a state Department of Natural Resources scientist and head of the Chesapeake Bay Program’s Bay grasses group.

Bay grasses, threatened by nutrient and sediment runoff, provide a crucial habitat and protection for blue crabs and other aquatic life. The grasses also filter the water by absorbing harmful nutrients and slowing the flow, allowing sediments to drop out, Karrh said.

The survey, conducted by the Virginia Institute of Marine Science, is based on photographs taken between May and October.

Grass coverage topped 90,000 acres in 2002 but saw sharp declines in 2006 to about 59,000 acres, according to the survey.

In 2007, the upper Bay, which is north of the Chesapeake Bay Bridge, reached 80 percent of the goal with 19,000 acres of coverage. The grass beds on the Susquehanna Flats have reached 97 percent of the goal.

“We are really excited about what we are seeing in the upper Bay,” said Bill Dennison, a researcher and professor at the University of Maryland Center for Environmental Science.

Grasses are responding to efforts to reduce the nitrogen loads through upgrading the wastewater treatment plants, Dennison said.

The middle and lower reaches of the Bay are still suffering from poor water clarity, researchers said.

The middle Bay, from the Bay Bridge to the Potomac River, saw grasses decrease to about 30,000 acres, or 26 percent of the goal, the survey found. South of the Potomac River, researchers found about 16,000 acres, or 35 percent of the goal.

smichael@baltimoreexaminer.com