Stormy Waters Ahead for Eelgrass

Environmental Commentary by Carrie Madren

Blades of eelgrass, flowing like ribbons, were once a ubiquitous sight in all of the major western shore tributaries and the eastern side of the bay. Beds formed an abundant habitat for blue crabs, sea horses, scallops and other species. Now, eelgrass (Zostera marina) coverage in the bay is a fraction of what it once was, and warming waters due to climate change threatens to compound problems for the hardy, high-salinity submerged aquatic vegetation.

Like oysters and other bay life, eelgrass offers valuable ecosystem services. First, eelgrass meadows create a rich habitat for small blue crabs, bay scallops, small fish and other marine life. Second, it improves water quality by using dissolved nitrogen and phosphorus, now excess nutrients in the bay. Using these nutrients curbs the growth of algae — a troublesome sunlight blocker. Third, eelgrass helps ease wave action, and helps settle suspended sediments in the water column. In turn, lower turbidity and algae growth help grasses to grow and spread, and settled sediments form rich growing medium.

Over the last century, eelgrass has had an uphill battle in Chesapeake waters. Coverage dropped dramatically in the early 1930s, when a wasting disease and a hurricane devastated populations, according to a report led by Bob Orth of the Virginia Institute of Marine Science; the SAV made a spirited recovery by the 1960s. But in 1972, Tropical Storm Agnes churned the bay, wiping out many stands of bay grasses of all kinds. By the mid-1970s, eelgrass had been reduced from half of its potential area. Eelgrass made a noble comeback between 1984 and the early 1990s. But run-off continued to worsen, stressing plants and slowing recovery.

Then, an unusually hot summer in 2005 — paired with high turbidity — raised water temperatures enough to greatly depress eelgrass meadows in the lower bay. The last five to 10 years have been particularly hard on Chesapeake eelgrass, which now grows mainly in the lower bay, where salinity is high.

Now and in the future, climate change may bring unusually high summer temperatures, which would continue to raise water temperatures and suppress eelgrass populations. As water temperatures rise, eelgrass requires more light to survive. In addition, climate change will likely bring more storms — and rainfall — which will boost sediment and nutrient content in tributaries.

Since the lower bay and the Virginia coastal region are already near the southern end of eelgrass range, warming water temperatures would push the range northward.

Virginia Institute of Marine Science researchers have examined how to bring back eelgrass since 1978 and monitored eelgrass since 1984. The U.S. Fish and Wildlife Service Migratory Bird and Habitat Research Laboratory and the Maryland Department of Natural Resources have been surveying aquatic grasses in Maryland waters for nearly 40 years as well.

And recently, researchers, including Orth, and conservation groups have been helping eelgrass make a successful comeback in the Virginia coastal bays near Oyster, Va.

The largest seagrass restoration project in the world takes place each year in the seagrass meadows of South Bay, off Oyster, Va., on the lower Eastern Shore. The project — started and led by the Virginia Institute of Marine Science — has broadcasted more than 37.8 million seeds on more than 300 acres in South, Cobb, Spider Crab and Hog Island bays since 1999; these seeded acres have naturally expanded to 2,430 acres of eelgrass meadows as of this year.

Seeds collected by The Nature Conservancy’s army of volunteer snorkelers are stored in continuously filtered, on-shore tanks that hold the pods until the seeds emerge. Then, seeds are strategically broadcast into waters where they create underwater, grassy habitat.

Since the massive restoration, conservationists have noticed crabs and other marine animals using the eelgrass beds, where a decade ago there was no eelgrass to be found.

Still, many Chesapeake restorations have been unsuccessful. Transplanting projects in the mid-section tributaries in the bay began in 1978, with little success beyond a couple years. The successful Atlantic coastal restoration has the advantages of relatively cooler water temperatures and clearer water with plenty of light penetration. If the Chesapeake had less turbidity, eelgrass would be able to deal with higher temperatures and make a faster comeback.

To re-establish eelgrass — and the marine life that depends on these habitats — we’ll have to improve water quality throughout the watershed. Cutting the amount of nutrients we allow into the bay — a common refrain through bay restoration discourse — will help eelgrass survive the rising temperatures and the increased storm challenges of climate change.

Carrie Madren writes about environmental issues, Chesapeake life and sustainable living. She lives in Olney, Maryland. Distributed by Bay Journal News Service.

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