Underwater Grasses Increase In Chesapeake Bay; Scientists Remain Concerned About Possible Losses

Chesapeake Bay underwater grass acreage increased 7 percent in 2005 to 78,260 acres, reaching 42 percent of baywide restoration goals, according to data released on May 25 by the federal-state Chesapeake Bay Program.

The 2005 acreage marks the second consecutive year of moderate gains for underwater grasses, which are critical to the bay ecosystem because they provide habitat for fish and shellfish, reduce shoreline erosion, absorb excess nutrients, and trap sediments. While the increased acreage is encouraging, scientists in Maryland and Virginia are concerned about 2006 abundance due to a widespread defoliation of eelgrass in lower and mid-bay areas that occurred several months after those areas were surveyed.

"The one-year acreage gain is good news for the bay -- in particular the increased acreage in the Potomac River and increased bed density on the Susquehanna Flats," said Professor Robert Orth of the Virginia Institute of Marine Science and project leader of the annual bay grass survey. "We hope the ecosystem has the resiliency to overcome the late-season loss of eelgrass in many parts of the lower bay. Last year's defoliation had not been observed on such a large scale since 1975."

Scientists believe last summer's unusually high water temperatures and calm conditions caused this unusual and extensive loss of eelgrass in the bay's higher salinity areas in August and September.

Scientists conducting field observations to assess the potential impact on 2006 bay grass abundance report that many areas are recovering rapidly, but the full recovery will not be known until late-June when aerial surveys of those areas are completed.

In the upper bay -- from the Chesapeake Bay Bridge north -- 19,464 acres of underwater grasses were mapped in 2005. While about ten percent lower than last year's record level of 21,673 acres, the average density of the beds increased, providing higher quality habitat for resident aquatic life. The density of grass beds in this area has been steadily increasing since 1999, following almost 15 years of sparse coverage. Bed density in this area has almost tripled since 1999, increasing from about 1,700 acres to nearly 5,000 acres of moderate- to high-density beds in 2005.

In the middle bay between the Chesapeake Bay Bridge and the Maryland/Virginia state line, last year's 39,576 acres marked a 17 percent increase, but is far below the previous high of 52,971 acres in 2002. Bay grass acreage in this region is dominated by widgeon grass, a species that shows tremendous inter-annual variability. The middle bay has seen two peaks since 1984, one in 1992-93, and one in 2001-02.

In the lower bay below the Maryland/Virginia state line, grasses covered 19,220 acres in 2005, a 9 percent increase from the unusually low acreage recorded in 2004. After a period of steady increase from 1984 through 1993, bay grass abundance in this region has fluctuated, generally averaging approximately 21,000 acres. Changes observed between 2004 and 2005 in some areas of the lower and mid-bay were likely a result of these beds beginning a recovery from the effects of Hurricane Isabel in 2003.

Because of their importance to the bay ecosystem, in 2002 the bay program partners committed to protect and restore 185,000 acres of bay grasses by 2010.

While acreage estimates fluctuate year to year, the bay as a whole has seen a slow increase in bay grass coverage from 38,000 acres in 1984 to nearly 90,000 acres in 2002. However, the record-setting decrease between 2002 and 2003 and the lack of resurgence in the middle and lower bay over the 21-year time period of the survey highlight the need to further reduce nutrient and sediment pollution flowing into the bay. Pollution reductions will help provide more suitable conditions for grasses by improving water clarity and allowing sunlight to reach grasses on the bay bottom.

More information about underwater grasses can be found at the Chesapeake Bay Program's Web site: http://www.chesapeakebay.net/baygras.htm.

This article originally appeared in the 05/01/2006 issue of Environmental Protection.

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