Submerged Aquatic Vegetation (SAV)
Sustain and increase the habitat benefits of submerged aquatic vegetation (SAV) in the Chesapeake Bay. Achieve and sustain the ultimate outcome of 185,000 acres of SAV Bay-wide necessary for a restored Bay. Progress toward this ultimate outcome will be measured against a target of 90,000 acres by 2017 and 130,000 acres by 2025.
Progress
Recent Progress: Increase
According to preliminary data from the Virginia Institute of Marine Science (VIMS), 67,470 acres of underwater grasses were mapped in the Chesapeake Bay in 2021. This is 52% of the Chesapeake Bay Program’s 2025 restoration target of 130,000 acres and 37% of the partnership’s 185,000-acre goal. The 67,470 acres mapped in 2021 is a 7% increase from the 2020 total of 63,132 acres, and therefore represents progress for this outcome.
Outlook: Off Course
The Submerged Aquatic Vegetation (SAV) Outcome is off course. Gains from 2020 to 2021 are positive, indicating an on-course trajectory, but these gains don’t yet offset the recent major declines of underwater grasses observed in 2019. Additional years of positive trajectory will help clarify whether this recent gain in 2021 is the start of a new positive trend toward higher levels of SAV across the Bay, but it is unlikely that the 2025 goal of 130,000 acres will be reached.
Submerged Aquatic Vegetation (SAV) Abundance (1984-2021)
*Estimated Additional Acreage: Factors such as adverse weather conditions, water clarity, or security restrictions over military air space prevented researchers from collecting aerial imagery. For these unmapped areas, estimates of SAV acreage are based on the prior year’s survey. Data was not collected in 1988.
Submerged Aquatic Vegetation (SAV) Abundance (2010-2021)
In 2021, 67,470 acres of SAV were mapped in Chesapeake Bay and its tributaries. However, weather conditions prevented acquisition of useable imagery for a portion of the Mattaponi and Pamunkey rivers. The area that was not fully mapped in 2021 supported 66 acres of SAV in 2020 (66 acres, 0.1% of the 2020 Bay total).
In 2021, all four of the Bay’s salinity zones experienced increases with the largest, an 18% increase, occurring in the Polyhaline zone:
- Tidal Fresh Zone: Underwater grass beds increased 4% from 18,514 acres to 19,239 acres, a 93% achievement of the region’s 20,602-acre goal.
- Oligohaline Zone (slightly salty): Underwater grass beds increased 2% from 8,231 acres to 8,397 acres, a 81% achievement of the region’s 10,334-acre goal.
- Mesohaline Zone (moderately salty): Underwater grass beds increased 5% from 22,686 acres to 23,768 acres, a 20% achievement of the region’s 120,306-acre goal.
- Polyhaline Zone (very salty): Underwater grass beds increased 18% from 13,701 acres to 16,132 acres, a 48% achievement of the region’s 33,647-acre goal.
Experts attribute the increases in the Polyhaline and Mesohaline zones to recovery from the SAV crash in 2019. The losses in 2019 were largely due to declines in widgeon grass, a species whose abundance can rise and fall from year to year in response to changes in water quality. For example, in 2018, widgeon grass increased in the Mesohaline and northern Polyhaline salinity zones, but subsequently declined in 2019, which mirrors a similar rapid increase in 2001 and 2002 that was followed by about a 50% decline in 2003.
While an increase in widgeon grass was observed in 2021, widgeon grass still remains in decline in some areas it was previously observed in. In 2021, the largest declines in terms of total area (-1,142 acres) were observed in widgeon grass dominated areas of the Mesohaline zone, including continued loss in Eastern Bay, the mouth of the Choptank River, and in the Little Choptank River.
In 2021, high density beds accounted for 62% of the total acreage, which is 9% higher than 2020. The density classifications for the beds in 2021 are as follows:
- 3% of the beds had densities of <10%(Class 1)
- 12% of the beds had densities of 10-40% (Class 2)
- 24% of the beds had densities of 40 -70% (Class 3)
- 62% of the beds had densities of 70-100% (Class 4)
Underwater grass beds are critical to the Chesapeake Bay ecosystem. They provide food and shelter to fish and wildlife, sequester carbon and buffer PH, add oxygen to the water, absorb nutrient pollution, reduce shoreline erosion and help suspended particles of sediment settle to the bottom. Because they are sensitive to pollution but quick to respond to improvements in water quality, underwater grass abundance is a good indicator of the Bay’s health. Before Europeans colonized the region, up to 600,000 acres of underwater grasses may have grown along the shorelines of the Bay and its tributaries. By the mid-1980s, nutrient and sediment pollution had weakened or eliminated many of these grass beds. While climate change, shoreline hardening and stressors that reduce water clarity will continue to impact our restoration success, many of these stressors can be managed with on-the-ground efforts to reduce pollution and research has shown that nutrient reductions made under the Chesapeake Bay Total Maximum Daily Load (Bay TMDL) have played a critical role in the overall underwater grass recovery documented since the Bay-wide aerial survey began in 1984.
More information about underwater grass abundance in the Chesapeake Bay can be found on the Virginia Institute of Marine Science (VIMS) website.
Management Strategy
To achieve this outcome, Chesapeake Bay Program partners have committed to:
- Supporting efforts to conserve and restore current and future underwater grass habitat and habitat conditions;
- Protecting existing and recovering underwater grasses;
- Restoring underwater grasses;
- Enhancing underwater grass research and monitoring; and
- Enhancing community involvement, education and outreach.
These partners will also collaborate with the work being done to achieve the 2025 Watershed Implementation Plans (WIPs) and Water Quality Standards Attainment and Monitoring outcomes.
Monitoring and assessing progress toward the outcome will occur through data related to underwater grass distribution and abundance.
As part of the Chesapeake Bay Program’s partnership-wide implementation of adaptive management, progress toward this outcome was reviewed and discussed by the Management Board in November of 2021. It will be reviewed and discussed by the Management Board again in November 2023.
Logic & Action Plan
Chesapeake Bay Program partners have committed to taking a series of specific actions that will support the management approaches listed above.
Participating Partners
The Submerged Aquatic Vegetation Workgroup, which is part of the Vital Habitats Goal Implementation Team leads the effort to achieve this outcome. It works in partnership with the Sustainable Fisheries and Water Quality goal implementation teams.
Participating partners include:
- Maryland Department of Natural Resources (State of Maryland)
- Maryland Department of the Environment (State of Maryland)
- University of Maryland Center for Environmental Science (State of Maryland)
- St. Mary’s College of Maryland
- Virginia Institute of Marine Science (Commonwealth of Virginia)
- Virginia Department of Environmental Quality (State of Virginia)
- Virginia Marine Resources Commission
- Virginia Coastal Zone Management Program
- Old Dominion University
- Department of Energy and Environment (District of Columbia)
- National Oceanic and Atmospheric Administration
- U.S. Army Corps of Engineers
- U.S. Environmental Protection Agency
- U.S. Fish and Wildlife Service
- U.S. Geological Survey
- Smithsonian Environmental Research Center
- Chesapeake Bay Foundation
- Local Riverkeeper and Watershed Organizations