BALTIMORE (AP) — Underwater grasses in the Chesapeake Bay continued to decline last year, and Hurricane Irene and Tropical Storm Lee the year before are to blame, researchers said Thursday as they released results of an aerial survey of the ecologically important aquatic plants.
The 2011 storms dumped a torrent of mud and debris into the bay, and that sediment, which can bury grasses and block them from the light they need to grow, is the most likely cause for the 21 percent drop. The decline was the third consecutive drop and follows a more than 20 percent decrease in the previous year’s study, which also blamed the storms as well as summer heat.
“It has been a rough few years for bay grasses, and we were not terribly surprised,” said Bob Orth, a Virginia Institute of Marine Science researcher who coordinates the survey.
The survey results were released by the Chesapeake Bay Program, a federal-state partnership that coordinates bay restoration efforts among the six states in the watershed — Maryland, Virginia, West Virginia, Pennsylvania, Delaware and New York — and the District of Columbia.
The amount of grass in the bay dropped to levels last reported in 1986, several years after the annual survey began, the researchers said. The die-off was least severe in the southern bay, where there was a 7 percent overall decrease and where new beds were found in the main stem of the James River.
Grass beds declined by nearly a third in the upper bay, but the survey found the large Susquehanna Flats grass bed remained very dense and robust. In the middle bay, which covers the section between the Bay Bridge and the Potomac River, grasses decreased 28 percent.
The grasses are important because they provide food and habitat for fish, birds and other species. They also absorb pollutants that can cause algae blooms and help clear the water.
An unusually hot summer in 2010 also caused some grasses to die off in the lower bay. That, combined with wet weather that washed sediments into the bay the following year, has contributed to the declines, the researchers said.
Nick DiPasquale, director of the Chesapeake Bay Program, said that despite the drop, the survey results still showed signs of resilience in the waterway and the results were a reminder of the importance of continuing restoration efforts.
Orth said he was reluctant to predict what might happen this year.
“If there’s no major event, I would expect that there might be some recovery in some parts of the bay,” Orth said.
However, he added that eel grasses, which are found in saltier waters lower in the bay, need clear, cooler waters. Decreasing water clarity is pushing the grasses into shallower areas where there is more light, but that also warm more easily in summer months, he said.
“This year is going to be highly dependent on our summertime temperatures,” Orth said.
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