Near-Record Heat and Pollution Cause 7 Percent Decline in Bay Grasses in One Year

A scorching early summer in 2010 and murky waters in the Chesapeake Bay contributed to a 7 percent decline over one year in underwater grasses that are critical habitat for crabs and fish, scientists announced today. 

“A lot of the grasses literally got cooked in June,” said Robert Orth, Professor of Marine Science at the Virginia Institute of Marine Science, who leads an annual aerial survey of Bay grasses.  "Global warming may have a big impact on the lower bay grasses.”

Another factor is water pollution, which muddies the water and feeds algal blooms that block the light that aquatic plants need to survive, said Lee Karrh, Living Resources Assessment Chief with the Maryland Department of Natural Resources.

"Eelgrass does not like hot water, but it can do alright if there is enough light," said Karrh, during a conference call with reporters this morning. "As soon as you start shading plants, they start to die."

The findings follow a 2005 heat-related die-off of grasses in the southern Bay that set off alarms among scientists about a possible connection between climate change and a decline of grasses in the lower Chesaspeake.  And the conclusion announced today reinforces the need for new federal Chesapeake Bay water pollution limits, which have been under attack by Farm Bureau lobbyists and their allies in Congress, led by Congressman Robert Goodlatte of Virginia.

"Some are arguing that the Bay is getting much better, and we do not need to impose further pollution reductions –- the so-called Bay pollution diet," said Will Baker, President of the Chesapeake Bay Foundation.  "Obviously, these data refute that."

The 7 percent (or 6,239 acre) decline in underwater grasses in the Bay from 2009 to 2010 follows a 7 percent increase the year before. The big picture is that underwater grasses in the Bay remain at less than half the levels they were in the early to mid 20^th century, before Hurricane Agnes in 1972 smothered many grass beds with muddy runoff.

Bay grasses have gradually expanded since that low point in the 1970s, and are now at 79,675 acres, or roughly double the roughly 35,000 acres of a quarter century ago, according to figures from EPA's Chesapeake Bay Program.  But despite those gains, grasses today remain at only about 43 percent of the level that scientists set as a goal because it reflects the historic potential of the Bay to support underwater vegetation.

Some interesting highlights from this morning's announcement by the Bay Program and scientists:

* In spite the past heat-related die-off of grasses in the southern Bay, the only section of the Chesapeake that experienced a slight increase in underwater vegetation last year was the southern Bay, which had a 1 percent growth. However, this increase was largely due to the spread of an invasive aquarium plant, called Hydrilla, in Virginia rivers that flow into the Bay. Also, some losses of underwater grass in this portion of the Bay may not have been accounted for, because the aerial survey of this part of the estuary was conducted in May and June, and grasses here may have died later in the summer.

* Grasses in the middle Bay declined by 11 percent, with large decreases in the Choptank, Honga, Patuxent and Potomac rivers. 

* Grasses in the upper Bay (from the Chesapeake Bay Bridge north) declined by 10 percent.  A few areas, such as the Chesapeake and Delaware Canal, and the Sassafrass River, experienced increases. But these rises were more than offset by losses in the Magothy, Bush, Bohemia and other rivers, according to the research results released today.

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By Tom Pelton

Chesapeake Bay Foundation

(Graphic: From Chesapeake Bay Program, with data from Virginia Institute of Marine Science)