The Chesapeake Bay’s submerged grasses are making a comeback
DELMARVA – Scientists say submerged aquatic vegetation, also known as SAV or sea grass, is making a comeback in the Chesapeake Bay.
SAV Making a Comeback
Between 2022 and 2023, researchers plotted about 82,937 acres of the plants throughout the Bay, marking a 7% increase.
“It looks good and is recovering,” said Brooke Landry, Program Chief of the Maryland Department of Natural Resources (MDNR) Living Resource Assessment. “The grasses in the mid and lower portion of the Bay did really well. The upper Bay didn’t do as well as normal.”
Recovering From Rough Year
However, more SAV may have grown than scientists could track; much of the data is collected using aircraft. Conditions need to be just right to get accurate readings.
“We’re looking for low tide, peak biomass for plants, low or no cloud cover, low wind, and the sun angle has to be right. It also has to be low turbidity,” said Chris Patrick, Director of the Virginia Institute of Marine Science SAV Monitoring and Restoration Program.
Patrick says that aerial data is usually supplemented by satellite imagery and boots-on-the-ground observations. “We can use that to validate aerial imagery, and we use that to map the spatial extent of all of the SAV meadows,” he said.
The new data indicates a 45% attainment of the ultimate goal of sustaining 185,000 acres of SAV in the Bay. By 2025, scientists hope to achieve 130,000 acres restored. However, SAV populations are still trying to bounce back from low numbers in 2019.
“2018 and 2019 were just really, really wet years,” Landry said. “It rained a lot, and when it rains a lot, you get a lot of runoff from the watershed, and you get increased nutrients [in the Bay.]”
Salinity Matters
To better understand the different types of SAV it’s home to, the Chesapeake Bay is grouped into four different salinity zones.
Underwater grass beds in the Tidal Fresh zone increased by 3% between 2022 and 2023. SAV in the Mesohaline (moderately salty) and Polyhaline (very salty) zones increased by 21% and 12%, respectively, in that same time period.
SAV in the Oligohaline (slightly salty) zone, however, fell 54% between 2022 and 2023. Researchers believe that phytoplankton blooms and suspended sediment may be to blame.
“That’s something that we’re going to work on, and I think it definitely emphasizes the need for continuing our monitoring programs and improving our monitoring programs,” Landry said.
The SAV in the saltier zones of the Bay may be the reason that overall populations are doing much better than they were previously. In 2023, the Polyhaline zone saw the largest amount of SAV since 1997.
Canary in a Coal Mine
Patrick says eel grass, which thrives in the Polyhaline zone, typically does not do well in hotter temperatures. So, the La Nina climate cycle, which has brought about cooler summers and below-average rainfall in recent years, could be helping them to better health. Improved water quality could also be the key.
“The grasses have been growing to deeper depths than we’ve seen in a long time,” Patrick said. “And, we think that is attributable, probably, to water quality improvement.”
It’s all a big cycle, Patrick says; he calls SAV the Bay’s proverbial canary in a coal mine.
“When the grass starts going downhill, that’s an indicator that there’s some kind of problem in the system,” Patrick said. “And, sea grass is a good indicator because it integrates, over a long period of time, a large number of factors.”
An Ecosystem Anchor
As Landry puts it, when SAV thrives, the whole ecosystem thrives. Without it, the Bay would be “a mud pit,” Landry says.
“It provides a really important habitat for many of the species, that we find in the Chesapeake Bay region, commercially, recreationally, and ecologically important,” Landry said.
In particular, SAV serves as a nursery ground for the iconic blue crab. In MDNR’s 2024 Bay-wide Blue Crab Winter Dredge Survey, researchers noted that the population of juvenile blue crabs was 138 million, an increase of 22 million from the year before.
SAV is also highly critical for helping to improve water quality. It does this in a number of ways, Landry says: filtering water, capturing nutrients, carbon, and acidic conditions, and helping to slow currents and reduce turbidity.
“It absorbs nitrogen and phosphorous and uses them to grow. That reduces the presence of algae blooms, and clarifies the water,” Landry said. “[SAV uses] CO₂ and outputs oxygen, and sequester carbon in the biomass of the plants… It creates a refuge for all of the animals that live in the Bay.”
Staying With Stewardship
All of this is why Landry says constant stewardship of SAV is so important.
The overall recovery of SAV has been documented by aerial survey since 1984, and researchers have noted marked improvements, thanks to the Chesapeake Bay Total Maximum Daily Load (Chesapeake Bay TMDL).
The Chesapeake Bay TMDL was implemented in 2010, as a means to put the Bay on a so-called “pollution diet.” It’s the largest such cleanup plan ever developed by the U.S. Environmental Protection Agency and sets limits on nutrient and sediment pollution. Delaware, Maryland, New York, Pennsylvania, Virginia, Washington, D.C., and West Virginia are all beholden to those limits.
Individuals can help by reducing fertilizer use in gardening or agriculture, cutting back on driving if they can, and using rain barrels. While individuals follow those practices, researchers are hard at work.
Scientists have been working with state and federal agencies to plant SAV in vulnerable areas. They’re also working on restoration experiments.
Plus, researchers are keeping a close eye on the numbers. If you want to get involved in that kind of work, Landry recommends checking out the SAV Watchers Program, in which everyday folks can help scientists collect data on SAV.
“There are a lot of different things that we as individuals can do to help improve the health of the watershed,” Patrick said.
