Meeting the Chesapeake Bay’s underwater grass restoration goal could soon get more difficult.
The state-federal Bay Program partnership may increase its goal for underwater grasses, an important habitat for blue crabs and many other species, from 185,000 to 196,000 acres.
Even the smaller of those numbers is more than double what’s been observed in the Bay in recent years, and the region has never come close to the 185,000-acre figure since Baywide measurements of the grass beds — officially called submerged aquatic vegetation, or SAV — began in the early 1980s.
Nonetheless, scientists and state officials say the goal should be updated to better reflect the amount of potential SAV habitat if the region meets its pollution reduction goals in the future.
The Bay Program established the 185,000 figure in 2003 using photographs from aerial surveys conducted during the 1900s — mostly old agricultural surveys — to map the location of all grass beds that could be seen in different parts of the Bay at some point in time.
Brooke Landry, a biologist with the Maryland Department of Natural Resources and chair of the Bay Program’s Submerged Aquatic Vegetation Workgroup, said that when the original maps were drawn, portions of some shoreline grass beds were inadvertently cut off in the mapping process, resulting in an underestimation of the observed amount.
Also, grass beds have been observed in recent years in some locations where they had not been previously mapped.
When those areas are included, the extent of Bay bottom that supports SAV, or is known to have done so at some point in the last century, increased to about 196,000 acres.
That updated figure is being proposed as a goal for the revised Chesapeake Bay Watershed Agreement, the policy document that guides Bay restoration efforts, which is being updated this year.
Landry acknowledged that meeting the goal will be difficult. While 196,000 acres of the Bay may have supported SAV at some point in time, it’s unclear whether that much ever existed in any single year during the past century.
The greatest extent of grass beds observed in recent decades was about 108,000 acres in 2018. Since then, the amount observed in annual aerial surveys has ranged from roughly 63,000 to 83,000 acres.
Underwater grass beds provide important habitat for many species, including waterfowl. They also buffer shorelines from waves, pump oxygen into the water, store carbon dioxide from the atmosphere and improve water quality.
Like all plants, though, they need light to survive, so grass beds began disappearing as the Bay’s water became cloudier from sediment and nutrient-fueled algae blooms.
Because of their significance, nutrient and sediment reduction goals for the Chesapeake were established, in part, to ensure that enough light would be available to support grass beds.
Chris Patrick, a scientist with the Virginia Institute of Marine Science who oversees the annual underwater grass survey that started in 1984, acknowledged that achieving the goal would be daunting. But he noted that grass beds have shown they can rapidly expand when conditions are right.
The Susquehanna Flats in the northern Bay, for instance, was mostly barren until around 2000, when grasses rapidly emerged and expanded, covering more than 10,000 acres today. And beds in Virginia’s coastal bays likewise mushroomed from almost nothing 20 years ago to more than 10,000 acres today.
“Seagrasses follow extremely non-linear trajectories once they get going,” he said. “The Susquehanna Flats is an example of a rapid recovery story that went from very little to a ton in a very short period of time, relatively speaking … If we can hit our targets for water quality, this stuff will bounce back rapidly.”