Despite record rainfall, underwater grass abundance remains strong

In 2018, an estimated 91,559 acres of underwater grasses were mapped in the Chesapeake Bay and its tidal tributaries. While this acreage is less than the previous year, it is likely that substantially more underwater grasses grew in the Bay than the mapped acreage suggests. Frequent rain, cloudy water and security restrictions prevented researchers from successfully collecting aerial imagery over the Potomac River near the Patuxent Air Base, as well as portions of the Susquehanna Flats; Mattaponi, Middle, Choptank and Honga rivers; and Fishing Bay.

Using 2017 levels for the unmapped areas, it is estimated that the Bay may have actually supported 108,960 acres of underwater grasses in 2018. This would mark a 59% achievement of the 185,000-acre goal adopted by Chesapeake Bay Program partners in the Chesapeake Bay Watershed Agreement. This would also be a 4% increase from last year’s total, which surpassed 100,000 acres, and was the highest amount of underwater grasses ever recorded in the Bay since monitoring began more than 30 years ago.

With the record-breaking rainfall observed by most of the Chesapeake region in 2018, experts were concerned about how the grasses would fare. This slight decrease in measured acreage suggests the Bay is increasing its resilience to such stressors, an indication that the restoration actions taken by the Chesapeake Bay Program are working.

“Last summer’s record rainfall—and the accompanying runoff and turbidity—definitely provided a stressful environment for our underwater grasses, but the fact that they had five solid years of expansion leading up to it helped the vast majority of the beds to survive,” said Brooke Landry, chair of the Chesapeake Bay Program’s Submerged Aquatic Vegetation Workgroup, in a media release. “Fluctuations in cover and abundance are totally natural, especially in response to varying weather conditions.”

“What we need to do now is to double down on our efforts to decrease nutrient and sediment pollution and give our underwater grasses a chance to continue their recovery,” Landry said.

Experts attribute the steady underwater grass abundance to the presence of widgeon grass in the middle and lower parts of the Bay. However, widgeon grass is a “boom and bust” species whose abundance can rise and fall sharply from year to year. Therefore, a widgeon-dominant spike is not guaranteed to persist in future seasons.

Underwater grasses—also known as submerged aquatic vegetation, or SAV—are critical to the Chesapeake Bay ecosystem. They absorb nutrients and trap sediment to maintain clean and healthy waters, slow wave action to help reduce shoreline erosion, provide food to small invertebrates and migratory waterfowl, and shelter fish and blue crabs.

In fact, because grass beds are important for protecting blue crabs, underwater grass abundance is also one of several factors influencing the health and stability of blue crab populations. Earlier this month, the annual Blue Crab Advisory Report found that the overall blue crab population increased nearly 60% from 372 million in 2018 to 594 million in 2019.

How you can help restore underwater grasses in the Bay

• Homeowners can use rain barrels or rain gardens to slow the delivery of nutrient- and sediment-laden stormwater runoff into the Bay.
• Waterfront landowners can limit hardened shorelines and instead opt for living shorelines.
• Boaters can trim their motors or steer clear of grass beds that are growing in shallow waters.
• Volunteers can help scientists and managers track grasses using the Chesapeake Bay SAV Watchers app, the first official underwater grasses monitoring program developed by the Chesapeake Bay Program. By downloading the app and joining the Chesapeake Bay SAV Watchers group, anyone with a smartphone can help monitor underwater grasses whenever and wherever they are on the water.

Track the progress of underwater grasses in the Bay at ChesapeakeProgress.