Chesapeake Bay Field Office
Northeast Region

Submerged Aquatic Vegetation: Where Have All the Grasses Gone?

Life Sustainers

These small and modest grasses are known as submerged aquatic vegetation or SAV. A habitat in itself, SAV provides functions invaluable to aquatic ecosystems like the Chesapeake Bay. More than a dozen species of SAV are native to the Chesapeake Bay. Salinity, water depth, and bottom sediment are factors which determine where each species can grow. However, the survival of all SAV depends on the amount of sunlight reaching the plants.

These amazing plants provide food and shelter for diverse communities of waterfowl, fish, shellfish, and invertebrates. Like all green plants, SAV produces oxygen, a precious and ever-decreasing commodity in the Chesapeake Bay. SAV filters and traps sediment, which can cloud the water and bury bottom dwelling organisms like oysters. SAV also absorbs nutrients like nitrogen and phosphorus.

Microscopic zooplankton feed on the decaying SAV and, in turn, are food for larger Bay organisms, such as fish and clams. Thus, SAV is a key contributor to the energy cycling in the Bay. SAV is a valuable source of food, especially for waterfowl. In the fall and winter, migrating waterfowl search the sediment for nutritious seeds, roots and tubers. Resident waterfowl may feed on different species of SAV year-round.

Like a forest, field or wetlands a SAV bed serves as habitat for a multitude of aquatic animals. Barnacles and scallop larvae attach to the leaves and stems of eelgrass in the salty waters of the lower Bay. Fish, like bluegill and largemouth bass, live in the freshwater grasses of the upper Bay. Minnows, small anadromous fish, like juvenile striped bass, and blue crabs seek protection as well as food in the SAV beds.

The Decline

Since the 1960s, well over half of the SAV has disappeared from the Bay waters. Declining water quality, disturbance of SAV beds, and alteration of shallow water habitat all contributed to the decline. The absence of SAV translates into a loss of food and habitat for many Chesapeake Bay species.The initial decline of SAV was most severe in the upper Chesapeake and western shore tributaries. Today, all areas of the Bay has experienced the decline of these important grasses.

The extensive loss of SAV has forced some species of waterfowl to migrate to other wintering areas or to change their feeding habits. Canvasbacks that continue to winter on the Bay now rely mainly on the Baltic clam as a primary food source. Other waterfowl, like redhead ducks, have all but abandoned the Chesapeake. As many as 80,000 redheads once stopped to feed on the Bay grasses. Now, only a few thousand redheads visit the Bay each year. Survival of SAV is affected most by the amount of light that reaches the plants. Reduction of light is the primary cause of the SAV decline. Environmental factors that affect water clarity also affect SAV growth.

Suspended sediment and other solids cloud the water, blocking precious sunlight from the grasses. Excessive amounts of sediment may cover the plants completely. Sources of sediment include runoff from farms, building sites, and highway construction. Shoreline erosion also adds sediment to Bay water. Land development, boat traffic and loss of shoreline vegetation accelerate natural erosion.

Nutrients, although vital to all ecosystems in natural levels, create problems when present in excess amounts. High levels of nutrients stimulate the rapid growth of algae, known as blooms. Algae blooms cloud the water and reduce the amount of sunlight reaching SAV. Certain types of algae grow directly on the plants, further reducing available sunlight.

Nutrients come from three major sources, sewage treatment plants, agricultural fields and fertilized lawns. Every day, more than one billion gallons of treated sewage effluent enters the Bay from treatment plants. This translates into 87 million pounds of nitrogen and 9 million pounds of phosphorus a year! Runoff from farm fields and lawns dumps tons of nutrient-rich fertilizers into the Chesapeake Bay each year. In addition to fertilizers, oils and other pollutants, runoff may also contain herbicides and pesticides that are toxic to aquatic organisms.

Restoring Grasses to the Bay

The U.S. Fish and Wildlife Service and other federal and state agencies, and the Virginia Institute of Marine Science monitor SAV distribution each year. By examining aerial photographs, locations of SAV are mapped for the entire Chesapeake Bay and its tidal tributaries. By monitoring SAV in Chesapeake Bay, biologists can determine which areas need to be protected. By examining historical distribution, areas where SAV once flourished are targeted for restoration.

Citizens also help track the presence of SAV by participating in a volunteer SAV survey. Those with access to shallow water habitats identify SAV beds that may be too small to be seen in the aerial surveys. Frequently, the information provided by volunteers is used by local officials in directing protection and management of waterways and shoreline areas.

Water quality is the key to restoring grasses to the Bay. Scientists have identified the water quality conditions and requirements necessary for the survival of different SAV species. Managers are using these requirements as the basis of recovery plans for various sections of the Bay and its rivers and creeks.

The presence or absence of SAV reflects the general water quality of an area. Like the proverbial canary in a coal mine, SAV can be used as a barometer to gauge the relative health of the Bay or any of its tributaries. Everyone who lives, works and plays in the Chesapeake Bay watershed, directly affects the water quality through everyday activities. The presence of SAV reflects our stewardship for the Chesapeake Bay and the wildlife it supports.

What You Can Do

  • Reduce the amount of fertilizers applied to yards.
  • Plant vegetation suited to your soil, moisture and climate conditions.
  • If you need to fertilize, follow all directions carefully; never apply before storms.
  • Prevent shoreline erosion by planting shoreline vegetation.
  • If you have access to shallow water areas, volunteer to survey SAV in your area.
  • When boating, avoid disturbing SAV beds. Propellers may tear rooted vegetation out of bottom sediments.
  • Waterfront property owners should avoid using herbicides that may harm delicate SAV plants.
Water Stargrass
Credit: Linda Hurley, USFWS

Water stargrass

In the shallow waters of the Chesapeake Bay, underwater grasses gently sway in the aquatic breeze of the current. Minnows dart in and out between the plants to graze on the microorganisms that grow on the stems and leaves. The grasses also provide refuge from larger and hungrier mouths. Sitting on the bottom, well hidden by the plants, a blue crab sheds its shell and waits for its new armor to harden.

Want to know more?

Read the report on the Decline of Submerged Aquatic Plants in Chesapeake Bay published in 1979 by the US Fish & Wildlife Service, Maryland DNR and the US Environmental Protection Agency

FWS/OBS-79/24 July 1979

Other SAV Resources:
MD Department of
  Natural Resources

Chesapeake Bay

Last updated: January 28, 2011