In 2013, there were an estimated 59,927 acres of underwater grasses in the Chesapeake Bay.
Date created: Apr 21 2014 / Download
Up until 2013, submerged aquatic vegetation (SAV, also known as bay grasses) acreage totals for the Chesapeake Bay were aggregated into three zones: Upper Bay, Middle Bay and Lower Bay. For 2013, it was decided to report the totals by the four salinity zones found in the Bay: tidal fresh, oligohaline, mesohaline and polyhaline. Since different species of SAV are generally found in waters of a specific range of salinity, tracking changes in SAV abundance by salinity could help track changes in species abundance more easily.
Bay grasses, also known as submerged aquatic vegetation, are an integral part of the Chesapeake Bay ecosystem. Lee Karrh from the Maryland Department of Natural Resources (DNR) explains what bay grasses need to grow and why their survival is important to Bay critters.
What is submerged aquatic vegetation, and why is it important to the Chesapeake Bay? Commonly known as “bay grasses” they among the most critical inhabitants of the Bay’s ecosystem. Find out more about submerged aquatic vegetation, and see what people around Baltimore’s Belvedere Square had to say about it.
Restoring underwater grasses to the rivers, streams and shallow waters of the Chesapeake Bay will dramatically improve the Bay ecosystem. Grass beds provide food and shelter to fish, crustaceans and other species, add oxygen to the water, absorb nutrient pollution, reduce shoreline erosion and help suspended particles of sediment settle to the bottom.
Underwater grasses—also known as submerged aquatic vegetation or SAV—are sensitive to pollution but quick to respond to improvements in water quality. This means their abundance is a good indicator of Bay health. As pollution declines and water clarity improves, scientists expect underwater grasses to expand.
In 2014, the Chesapeake Bay Program renewed its goal to achieve and sustain 185,000 acres of underwater grasses in the Chesapeake Bay. Progress toward this goal will be measured against a target of 90,000 acres by 2017 and 130,000 acres by 2025.
While the Bay Program previously reported underwater grass acreage in three geographic zones, these data were re-aggregated in 2013 into four salinity zones. Each salinity zone has its own restoration goal.
Reviews of photographs from a number of sites dating back to 1937 suggest that close to 200,000 acres of underwater grasses may have once grown along the shorelines of the Chesapeake Bay. By 1984, nutrient and sediment pollution had weakened or eliminated grass beds in many areas, contributing to a Bay-wide SAV decline.
Long-term trend (1984-2013)
Short-term trend (2004-2013)
Change from previous year (2012-2013)
To see Bay-wide trends in underwater grass abundance, visit our Underwater Bay Grass Abundance (Baywide) indicator.
This data is collected through an aerial survey flown by researchers with the Virginia Institute of Marine Science (VIMS) from late spring to early fall. VIMS processes the photography in fall and winter and provides preliminary area totals the following spring. Visit the VIMS SAV website for more information about the aerial survey or for segment-specific survey results.
When scientists began to collect underwater grass abundance data in 1984, the Chesapeake Bay was divided into three geographic zones:
For almost 30 years, underwater grass acreage was reported in these geographic zones. But these zones span a wide range of salinities and do not account for salinity-related changes in underwater grass communities. Because the makeup of grass communities changes as salinity increases—and because these communities respond differently to heat, drought, storms and other events—it makes more ecological sense to report underwater grass acreage by salinity zone than by geographic zone. This can also help scientists find patterns in how underwater grasses are growing.
Based on an analysis of the distribution and long-term trends of underwater grass species in the Bay (Moore et al., 2000; Orth et al., 2010), there are three or four distinct underwater grass communities that can be delineated by salinity range. These correspond to the four salinity zones used to report underwater grass abundance:
Virginia Institute of Marine Science