by Alicia Pimental
September 01, 2007
Since 2004, the Maryland Department of Natural Resources (MD-DNR) has been developing and applying large-scale bay grass restoration techniques at its Piney Point Aquaculture Center on the Potomac River in St. Mary's County.
Bay grasses, also known as submerged aquatic vegetation or SAV, once grew in abundance in the shallows of the Bay and its tributaries. The underwater grasses are vital to a healthy Bay ecosystem because they provide protection and nursery habitat for fish and blue crabs, filter and oxygenate the water, and help reduce shoreline erosion.
Currently, there are about 32,000 acres of bay grasses in the Maryland portion of the Chesapeake - approximately 30 percent of the state's 114,000-acre restoration goal. Progress toward the bay-wide goal of 185,000 acres of grasses is similar, at about 32 percent.
While the best way to restore bay grass populations is through water quality improvements, bay grass restoration activities also play an important role. Since 2004, MD-DNR has seeded nearly 70 acres of suitable, unvegetated habitat to help jumpstart natural, established bay grass beds.
MD-DNR staff are currently working to restore bay grasses—specifically eelgrass, a particularly beneficial species—by collecting seeds from healthy eelgrass beds in the spring and distributing them in promising areas of the lower Potomac River.
Each May, scientists and volunteers collect seed-bearing shoots from eelgrass growing in Tangier Sound, near Crisfield on Maryland's Lower Eastern Shore. The seed material is then transported by boat across the Bay to the Piney Point Aquaculture Center to be processed, stored and distributed.
MD-DNR staff members at Piney Point are currently evaluating two eelgrass seed dispersal methods to determine the most cost-effective way to re-establish eelgrass beds.
The first takes place almost immediately following the late spring seed collection, using seed bags.
- Seed-bearing shoots are loaded into mesh bags, which are placed at suitable seeding sites. The bags attached to a heavy block that keeps the bags from drifting away from the site.
- The seeds gradually fall through the mesh of the bags and settle to the bottom, imitating the natural distribution of eelgrass seeds in the wild.
- Results vary among different sites, but about 1.5 to 2 percent of the 200,000 to one million seeds in each bag germinate into seedlings.
While this technique is similar to the way eelgrass seeds naturally drift and scatter, the seeds distributed in the spring won't turn into seedlings until the fall. That's because eelgrass is a cool-water species that typically does not thrive during the Chesapeake 's hot summer months. However, many things can happen to the seeds over the summer while they are not growing—including natural predation, burial by sediments and being carried away from favorable areas.
The MD-DNR staff also works actively with researchers from the Virginia Institute of Marine Science (VIMS) and St. Mary's College of Maryland to refine a second method for seed processing, storing and distribution. This method was originally developed by VIMS and is now being carried out on a large scale at the Piney Point facility.
Seed processing begins once seed material is brought from Crisfield in May. Seed shoots are processed to separate the seeds, then stored for the summer. Distribution takes place in the fall, when natural eelgrass seed germination occurs.
The collected material is placed in several 20,000-gallon aerated holding tanks. The eelgrass seeds grow into grasses, then die and decay.
Over a period of about a month, the seeds separate from the grasses and non-seed material and sink to the bottom of the tanks. The seed slurry—a muddy substance—is then pumped through a series of settling tanks and filter screens to remove the non-seed material.
The eelgrass seeds are placed in small temperature- and salinity-controlled tanks until fall, when they are distributed (by hand and mechanically) in suitable areas of the lower Potomac River.
MD-DNR scientists monitor the seeding sites throughout the eelgrass growing season (March through November) to determine the effectiveness of both distribution techniques. In addition, nearby water quality monitoring information is also collected to help explain changes in the overall health of eelgrass beds.
Scientists at VIMS are conducting similar restoration efforts in Virginia waters.