Underwater grass abundance, ‘critical’ to the Chesapeake Bay’s ecosystem, is down but may be stabilizing

The abundance of underwater grasses in the Chesapeake Bay — responsible for cleaning water, slowing wave movement and sustaining blue crabs and other marine life — declined for the second year in a row, according to the Chesapeake Bay Program.


Surveyors mapped an estimated 62,169 acres of underwater grass in the Chesapeake Bay and its tributaries in 2020, down 7% from 2019 and 20% from the bay’s average expanse of underwater grass over the last 10 years, according to the bay program.

While the declines in what’s also known as submerged aquatic vegetation are not good for the bay’s overall health, the program noted that last year’s decline was not as severe as the year before when the grasses fell from 108,878 acres in 2018.


“The silver lining is that the 2020 survey shows that underwater grasses are stabilizing following the losses experienced in the middle Bay in 2019,” said Chris Patrick, head of the Chesapeake Bay restoration program at the Virginia Institute of Marine Science, which monitors underwater grass populations. “We are hopeful that this is a sign that we’re poised to start regaining that lost ground in coming years.”

The largest decline in underwater grass was seen in Tangier Sound, the Eastern Bay and areas of the Choptank River, all waters with moderate salt levels, according to the program.

The program said these losses are likely due to a repeated decline in widgeon grass, a delicate seagrass with an often fluctuating population that doesn’t take kindly to extreme weather and changing water conditions.

“It is becoming imperative that we learn more about the life history and biology of this species, as our hope of continued underwater grass recovery in much of the Bay is becoming increasingly tied to the success or failure of this one species,” Patrick said.

The primary concern about the loss of underwater grasses in the Bay comes down to one thing: blue crabs, which shelter from predators in the grass beds.


The population of young blue crabs declined from 185 million in 2020 to 86 million in 2021, according to the Blue Crab Advisory Report, and it’s not due to overfishing.

“Researchers that study underwater grasses believe that a contributing factor to the decline of the juvenile blue crab population is the decrease of grass beds from 2018 - 2020,” the Bay Program said in the release.

In order to support grass populations in the Bay, and therefore blue crab populations as well, it comes down to improving water quality and minimizing extreme climate events, according to the program.

“We need to sustain the efforts we’ve already made — because we know those efforts have paid off — but in the face of climate change, we’re going to need to do more,” said Brooke Landry, chairperson of the Chesapeake Bay Program Submerged Aquatic Vegetation Workgroup and natural resource biologist with the Maryland Department of Natural Resources. “It’s not just about nutrient and sediment pollution anymore; it’s managing those things plus dealing with all of the other stressors associated with climate change. It’s daunting but saving the Bay’s underwater grasses is absolutely worth it.”