Underwater Bay Grasses

More than 16 species of underwater bay grasses — also called submerged aquatic vegetation or SAV — are found in the Chesapeake 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 the overall health of the Bay.

How Are Bay Grasses Important?

Bay Grasses 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.

Bay Grasses Keep the Chesapeake Bay Clear and Healthy

Healthy bay grass beds help keep the Chesapeake Bay clean by:

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

What Types of Bay Grasses Grow in the Chesapeake Bay?

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.

Learn more about the most common underwater bay grass species in the Chesapeake Bay and its tributaries.

How Do Bay Grasses Grow?

Just like plants on earth, underwater grasses go through photosynthesis, so they need sunlight to grow. 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 stormwater runoff that is polluted with nutrients and sediments.

• Excess suspended sediment clouds the water, preventing sunlight from reaching bay grasses.
• Excess nutrients fuel the growth of algae blooms, which also block sunlight from reaching bay grasses.
• 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.