by Stephanie Smith
July 18, 2017
The plants that grow in the shallow waters of the Chesapeake Bay and its rivers, streams and creeks are a critical part of the Chesapeake Bay ecosystem. Known as underwater grasses or submerged aquatic vegetation (SAV), they improve water quality by reducing erosion, trapping loose sediment and absorbing nutrient pollution. During photosynthesis, they add the dissolved oxygen to the water underwater critters need to survive. They also serve as habitat for vulnerable young fish and crabs and provide food for migrating waterfowl.
Below, learn about five types of underwater grasses that are found in the Chesapeake Bay.
This underwater grass prefers the saltier waters of the middle and lower Chesapeake Bay, making it one of the dominant species in the Virginia portion of the Bay. Its long, ribbon-like leaves can grow up to four feet long, but vary in size depending on the plant’s location.
Eelgrass provides important habitat for blue crabs: juveniles and molting adults forage for food and hide from predators among eelgrass beds. But warming water temperatures resulting from changes in climate may threaten future eelgrass abundance, as this sensitive plant becomes distressed when waters are warmer than 86 degrees Fahrenheit for long periods of time.
The delicate, thread-like widgeon grass prefers saltier waters, ranging from the slightly brackish upper Bay through to the saltier lower portion. Like eelgrass, it is one of the dominant underwater grass species found in the Virginia portion of the Bay. Widgeon grass is also known as ditch grass, because it sometimes grows on land in the ditches alongside roads and farm fields.
In recent years, a strong increase in the amount of widgeon grass has helped the Bay reach record acreages of underwater grass beds. However, because widgeon grass is a “boom and bust” species—its abundance can rise and fall from year to year—scientists caution that a widgeon-dominant spike is not guaranteed to last.
Perhaps one of the prettiest underwater grasses, water stargrass is named for the distinctive yellow, star-like flowers that bloom along its freely-branching stems. It grows in the fresh waters of the upper Bay and in tributaries throughout the region.
If water stargrass washes ashore, it can sometimes grow on land; the terrestrial form also produces the characteristic flowers, but its leaves are small and leathery. This form of water stargrass is sometimes called the mud plantain.
The invasive hydrilla grows in freshwater portions of the Bay and its tributaries, although it has also been found in some saltier waters. Its long, branching stems are covered in tiny leaves with teeth along the edges. Because hydrilla does not need as much light as other underwater grasses, it can be found in murkier waters with more sediment pollution.
Introduced to the United States in the 1960s through the aquarium trade, hydrilla was first detected in the Chesapeake Bay region when it was found in the Potomac River near Washington, D.C., in 1982. Within a decade, it had grown to cover 3,000 acres of the river.
Similar in appearance to eelgrass, the long, ribbon-like leaves of wild celery can be distinguished by the light green stripe running down the center of each leaf. Wild celery grows in fresh and slightly salty waters throughout the region, including the upper Chesapeake Bay and its tidal and non-tidal tributaries. Hardier than other underwater grasses, wild celery can withstand disturbance from waves and is more tolerant of murky, pollutant-rich waters.
Many underwater grasses serve as an important food source for critters, but wild celery’s buds and roots are particularly important to waterfowl as they migrate and overwinter in the Bay region. In fact, the scientific name for the canvasback, Aythya valisineria, comes from the first part of wild celery’s scientific name, Vallisneria americana.
Underwater grasses are sensitive to pollution: as excess nutrients and sediment flow into the Bay, low-oxygen dead zones and cloudy waters deprive the plants of the oxygen and sunlight they need to survive. In the 1950s and 60s, declining water quality caused many underwater grass beds—which once grew so thick that boats were unable to move through them—to disappear.
Today, Chesapeake Bay Program partners are working to restore underwater grasses across the estuary. Last year, more than 97,000 acres of underwater grasses were recorded, marking a 53 percent achievement of our partners’ 185,000-acre goal.