Underwater Bay Grasses

More than 16 species of underwater bay grasses — also called submerged aquatic vegetation or SAV — are found in the Bay and its tributaries. Bay grasses are an excellent measure of the Bay's overall condition because they are not under harvest pressure and their health is closely linked to water quality.

How are bay grasses important?

Provide food and shelter

Underwater bay grasses form plant communities that provide food and habitat for many species of fish, shellfish and waterfowl.

• Female blue crabs hide within bay grass beds after molting, when their soft shells make them especially vulnerable to predators. Other crustaceans, as well as mollusks and small fish, also find refuge from larger predators among the grasses.
• Bay grasses serve as protective nurseries for young crabs and fish, including menhaden, herring, shad, spot, croaker, weakfish and white perch. Bay scientists have found 30 times more juvenile blue crabs in bay grass beds than in areas with no grasses.
• Barnacles, sponges, sea slugs, sea squirts and other tiny crustaceans feed on and attach themselves to bay grasses.
• Many bay grass species are a valuable food source for migrating and resident waterfowl.
• Microscopic zooplankton feed on decaying grasses. In turn, zooplankton serve as food for larger organisms.
• Minnows graze on tiny organisms that grow on the stems and leaves of bay grasses.

Improve water quality

In addition to providing food and habitat, healthy bay grass beds also help keep the Bay healthy by:

• Adding oxygen to the water during photosynthesis.
• Trapping and anchoring sediment that would otherwise cloud the water and bury bottom-dwelling species.
• Softening wave action that can erode shorelines.
• Absorbing excess nutrients.

Where do bay grasses grow?

Salinity is the main factor that determines where a particular bay grass species can grow. For example:

• Eelgrass and widgeon grass prefer the high-salinity waters of the lower Bay.
• Redhead grass and sago pondweed grow in the fresh and brackish waters of the upper Bay.

How do bay grasses grow?

Just like plants on earth, underwater grasses go through photosynthesis. Sunlight must be able to pass through the water to reach bay grasses at the bottom, or the grasses cannot produce enough food and energy to grow. In recent decades, bay grass growth has been hindered by polluted runoff containing nutrients and sediment.

• Excess suspended sediment clouds the water, preventing sunlight from reaching bay grasses.
• Excess nutrients can cause increased algae growth, which also blocks sunlight from penetrating through the water.
• Unusual weather events, including extreme drought or very wet summers with intense storm activity, can also affect bay grasses.

While bay grasses are quite sensitive to pollution, they respond fairly quickly to improvements in water quality, making them an excellent barometer of the Bay's overall health.