More than 97,000 acres of underwater grasses recorded in Chesapeake Bay

An estimated 97,433 acres of underwater grasses were mapped in the Chesapeake Bay in 2016, the highest amount ever recorded in more than 30 years of aerial surveys by the Virginia Institute of Marine Science. The total marks a 53 percent achievement of the 185,000-acre goal adopted by Chesapeake Bay Program partners in the Chesapeake Bay Watershed Agreement.

In addition, even more underwater grasses likely grew in the region than the estimate suggests. Due to weather conditions and security restrictions, researchers were unable to collect aerial imagery over a portion of the Potomac River. In 2015, the portion supported almost 2,000 acres of grasses, and trends suggest that—had it been mapped—the area would have put the Bay-wide total at 99,409 acres.

Experts attribute the rise in underwater grass abundance to a strong increase in the tidal freshwater and moderately salty regions of the Bay, with widgeon grass in particular expanding in the latter region. However, because widgeon grass is a “boom and bust” species—its abundance can rise and fall from year to year—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 Bay ecosystem. They provide food for small invertebrates and migratory waterfowl and maintain clear and healthy waters by absorbing nutrients, trapping sediment and slowing shoreline erosion. Although sensitive to pollution, underwater grasses are quick to respond to improvements in water quality, making their abundance a good indicator of Bay health.

“As a bay grass biologist, it is thrilling to see SAV recovering in the Chesapeake. Bay grasses exceeded our 2017 midterm goal of 90,000 acres for the second year, with reports of recovering SAV species diversity in areas throughout the Bay as well,” said Maryland Department of Natural Resources Biologist and Submerged Aquatic Vegetation Workgroup Chair Brooke Landry in a media release. “With continuing commitments to further reduce pollutants entering the Bay’s waters, I believe it’s possible to reach records every year and foster thriving SAV beds throughout the Bay—SAV beds that will promote ecological resilience and provide economic and recreational opportunities for generations to come.”

Because grass beds provide shelter for young fish and blue crabs, underwater grass abundance is also one of several factors influencing the health and stability of blue crab populations. Earlier this month, data collected by Maryland and Virginia through the Blue Crab Winter Dredge Survey showed that, while the overall blue crab population fell 18 percent between 2016 and 2017, the abundance of adult female crabs increased from 194 million to 215 million: the highest amount ever recorded by the Winter Dredge Survey.

In addition to financially supporting the aerial surveys used to monitor underwater grasses, the Chesapeake Bay Program has funded a citizen science project in which local riverkeepers, watershed organizations and volunteers can collect data on underwater grasses. As part of this project, Chesapeake Commons is expanding its Water Reporter app to include underwater grass monitoring features. 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.