The underwater grasses of the Chesapeake Bay and its tributaries grew by 7% in 2023, contributing to improved water quality and providing food and shelter for the species that live there.
The SAV Restoration and Monitoring Program at the Virginia Institute of Marine Science mapped 79,234 acres of submerged aquatic vegetation, or SAV, in the Bay last year. Using 2022 data to account for areas that were unmapped in 2023, the program’s scientists estimated 82,937 acres of SAV in the Bay. That marks the third consecutive yearly increase.
But grass acreage remains down from a high of 108,078 acres in 2018, and the growth last year was not felt evenly across the Bay.
Freshwater parts of the Bay saw underwater grass beds grow by 3%, while grasses increased by 21% in moderately salty areas and 12% in very salty areas.
The Bay’s very salty zone reported its highest acreage of grasses since 1997, which the scientists said could be attributed to a La Niña climate cycle, with cooler summers supporting eelgrass.
Underwater grasses fell by 54% in slightly salty areas, due in part to partial mapping of the zone in 2023 as well as the loss of grasses in the middle Potomac River, the Gunpowder River, and other rivers in the upper Bay. Phytoplankton blooms and suspended sediment could have contributed to declines in that zone.
The Chesapeake Bay received a C+, its highest score since 2002, in an annual report card released last month by the University of Maryland Center for Environmental Science. Improvements for aquatic grasses, among other factors, contributed to that overall score. The report card did note decreased grades for aquatic grasses and other measures in the Upper Western Shore.
Historically, the Bay has supported anywhere from 200,000 to 600,000 acres of grasses along its shoreline based on photographic evidence dating back to 1937, according to the Virginia Institute scientists. But that number plummeted to about 38,000 acres by 1984.
Although grasses have improved over the past 40 years, they remain significantly lower than those historic levels.
In 2019, Chesapeake Bay grasses dropped to 66,684 acres, largely a result of the decline of widgeon grass, which can fluctuate based on water quality and weather conditions, according to the scientists.
However, the scientists point to the continued growth of underwater grasses over the past few years as a sign of the Bay’s improving health.
“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,” they wrote.
The new survey data represent “a bright spot in a longer history of mixed results for Bay grass restoration,” said Alison Prost, Vice President for Environmental Protection and Restoration at the Chesapeake Bay Foundation.
She pointed to benefits to Bay species like blue crabs, which use underwater grasses for shelter, protection from predators, and reproduction.
But Prost also cautioned that more progress is still needed.
“We must dramatically reduce pollution long-term to give the Bay’s underwater grasses a fighting chance in the face of climate change and rising seas,” she said in a statement.
States party to the Bay Watershed Agreement, including Maryland, set a goal of 185,000 acres of underwater grasses in the Chesapeake Bay and its tributaries by 2025. The CBF said the Bay states will not meet many of the targets in that agreement by the deadline.
“For a healthier future Chesapeake Bay, Bay watershed leaders must recommit to the Bay partnership this December and chart a future course for Bay restoration that addresses new challenges like climate change and reflects scientific updates,” Prost said. “Those scientific recommendations include focusing restoration efforts on shallow-water habitat. If that is done, we could reach the 185,000-acre goal.”
