Underwater Bay Grasses
Bay grass beds provide critical habitat for molting blue crabs, juvenile finfish and other Bay inhabitants.
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 underwater bay grasses important to the Bay?
Underwater bay grasses form plant communities that provide important food and habitat for many species, including fish, shellfish, invertebrates and waterfowl.
- Minnows graze on the tiny organisms that grow on the stems and leaves of bay grasses.
- Microscopic zooplankton feed on decaying grasses; in turn, zooplankton serve as food for larger organisms.
- Barnacles, sponges, isopods, amphipods, sea slugs and sea squirts all feed on and attach themselves to bay grasses.
- SAV beds are vital to female blue crabs, which hide among grasses 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 many juvenile fish and invertebrates, including blue crabs, 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.
- Many SAV species are a valuable food source for migrating and resident waterfowl.
Healthy bay grass beds also help improve water quality by:
- Adding oxygen to the water during photosynthesis.
- Trapping and anchoring sediment that would otherwise become suspended, clouding the water and burying benthic organisms.
- Softening wave action that can erode shorelines.
- Absorbing excess nutrients, which bay grasses need to grow.
Video footage of an underwater bay grass bed in the lower Chesapeake Bay. Courtesy: Morgan Wells
How do underwater bay grasses grow?
Salinity is the main factor influencing where a particular underwater 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 brackish waters of the upper Bay.
Just like plants on earth, underwater bay grasses go through photosynthesis and thus need sunlight to grow. If the sun's rays are not able to filter through the water and reach SAV at the bottom, the grasses cannot produce enough food and energy to grow.
Over the past few decades, SAV growth in the Bay has been hindered by runoff containing nutrients and sediment.
- Excess suspended sediment clouds the water, preventing light from reaching bay grasses.
- High nutrient levels can cause excess algae growth, which also blocks sunlight from penetrating through the water.
Unusual weather events, such as extreme drought or very wet summers with intense storm activity, can also affect bay grasses. Even though SAV are quite sensitive to changes in water quality, they respond fairly quickly to improvements in environmental conditions. This makes bay grasses an excellent barometer of the Bay's overall health.