by Alicia Pimental
October 01, 2008
Over the past five years, the NOAA Chesapeake Bay Office and the U.S. Army Corps of Engineers have led innovative new research to increase the amount of underwater grasses in the Chesapeake Bay.
Bay grasses are vital to the Bay ecosystem because they provide food for migratory waterfowl and habitat for juvenile fish and blue crabs. They also add oxygen to the water, stabilize bottom sediments and slow shoreline erosion.
In recent decades, bay grass growth has been hindered by polluted runoff containing nutrients and sediment, negatively affecting both water quality and the fish and crabs that depend on bay grasses for their survival. The decline of bay grasses spurred the Bay Program to set a goal to restore 185,000 acres of bay grasses by 2010, including an ambitious goal to plant 1,000 acres of bay grasses by the end of 2008.
Traditionally, bay grass restoration efforts focused on hand-planting adult grasses, which was labor-intensive, costly and had mixed results. Furthermore, these earlier restoration projects were often small and uncoordinated, without consistent methods.
As part of efforts to meet the Bay Program’s bay grass restoration goals, NOAA and the Army Corps Engineer Research and Development Center (ERDC) contributed approximately $4 million from 2003 through 2006 to develop procedures for large-scale bay grass restoration. This is the largest coordinated, multi-federal agency effort to date on bay grass restoration.
“We quickly realized that if we were going to be able to plant large acreages of underwater grasses, we needed to take an agricultural approach,” said Deborah Shafer, research marine biologist for the Army Corps ERDC.
Just as farmers plant seeds to grow crops, scattering bay grass seeds instead of planting adult grasses was found to be the most cost-effective way to restore large, self-sustaining bay grass beds.
“The work funded by NOAA and the Army Corps focused on a variety of research topics, starting with developing a basic understanding of seed ecology and germination issues,” said Peter Bergstrom, biologist with the NOAA Chesapeake Bay Office. “We then started applying this knowledge to large-scale restoration, including improved methods for seed collection, storage and dispersal.”
At first, researchers tried two methods of collecting seeds from existing bay grasses: using divers to hand-collect seed shoots, and using a mechanical harvester that cuts off seed shoots, much like a lawn mower cuts grass. The mechanical harvesting proved to be the most cost-efficient method for collecting seeds.
Researchers also compared two different techniques for spreading bay grass seeds. The first involves putting the seed shoots right after they are collected in large, floating mesh bags, which allow the seeds to slowly disperse. These “seed buoys” have been found to yield high seedling rates under some circumstances. But seeds dispersed using this method yield fewer seedlings because 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 second method uses a special aquaculture process to separate the seeds from the shoots. The seeds are then stored until fall, when they are scattered by hand and mechanically. The aquaculture method allows seeds to be distributed during the same time of year when natural grass seed germination occurs.
(Learn more about the two methods of planting bay grass seeds.)
From 2003 through 2006, scientists with NOAA, ERDC and other Bay Program partners distributed 133 acres of bay grass seeds, an average of 33 acres per year. In comparison, only 9 acres of grasses were planted per year from 1983 through 2003 using the traditional method of hand-planting adult grasses.
Seeds were planted in select locations throughout the Bay, including 16 million seeds over 101 acres of Virginia’s Piankatank River and Maryland’s Patuxent and Potomac rivers, and more than 1 million seeds over 15 acres at Poplar and Barren islands on Maryland’s Eastern Shore.
While the agricultural method of planting seeds resulted in more acres of bay grasses planted than hand-planting adult grasses, very few seedlings became established. However, because of the large number of seeds distributed, even low seedling establishment rates can mean many seedlings.
“Seed-based restoration does hold promise, though challenges remain, including improving seedling success rates and the long-term survival of seedlings with the Bay’s marginal water quality,” said Robert Orth, scientist with the Virginia Institute of Marine Science.
Just outside of the Chesapeake, bay grass restoration efforts have had more successful results. In Virginia’s coastal bays, scientists with the Virginia Institute of Marine Science are using very similar methods to conduct underwater grass seedings. Since 1998, 30 million seeds have been scattered in four coastal bays over 190 acres that had no seagrass beds. Today, over 1,000 acres of these bays are covered by seagrass, showing the importance of clean water to underwater grass growth.
“Concurrent water quality and environmental monitoring in these bays has shown that parameters such as light attenuation, algae and temperature are within the range necessary for growth and expansion of seagrass beds,” Orth said.
Details about the status of underwater bay grass restoration in the Bay are available in the technical report Large-Scale Submerged Aquatic Vegetation in Chesapeake Bay, published by ERDC.
Other partners involved with the bay grass research and restoration effort include the Virginia Institute of Marine Science, the University of Maryland Center for Environmental Science Horn Point Laboratory, the Maryland Department of Natural Resources and Anne Arundel Community College.
bay grasses (SAV)