In 2016, preliminary data indicates an estimated 97,433 acres of underwater grasses were mapped in the Chesapeake Bay: 7,433 acres greater than the Chesapeake Bay Program’s 2017 restoration target and 53 percent of the partnership’s 185,000-acre goal.
For the second year in a row, the 2016 total is the highest amount ever recorded by the Virginia Institute of Marine Science. Moreover, it is likely that more submerged aquatic vegetation grew in the region than this estimate suggests: weather conditions and security restrictions prevented researchers from collecting aerial imagery over a portion of the Potomac River. This portion of the Potomac supported almost 2,000 acres of grasses in 2015, and trends suggest this area would have put the Bay-wide total at 99,409 acres—or 54 percent of the goal—had it been mapped.
Researchers attribute the rise in underwater grasses to a strong increase in the tidal freshwater and moderately salty regions of the Bay. The iconic grass beds at the mouth of the Susquehanna River, for instance, continued their four-year recovery following damage from Hurricane Irene and Tropical Storm Lee. And at over 10,000 acres, the grasses that stretch from Smith Island to Tangier Island have become the biggest contiguous grass bed in the Bay. Widgeon grass, in particular, expanded in this bed and other moderately salty waters, but because it is a “boom and bust” species whose abundance can rise and fall from year to year, a widgeon-dominant spike is not guaranteed to persist in future seasons. Researchers observed a drop in the eelgrass that grows in the very salty waters of the lower Bay, where beds had increased in recent years following losses that occurred during the hot summers of 2005 and 2010.
Underwater grasses—also known as submerged aquatic vegetation or SAV—are sensitive to pollution but quick to respond to improvements in water quality. While close to 200,000 acres of underwater grasses may have once grown along the shorelines of the Bay and its tributaries, nutrient and sediment pollution had weakened or eliminated many of these grass beds by the mid-1980s. Because grass beds provide food and shelter to fish and wildlife, add oxygen to the water, absorb nutrient pollution, reduce shoreline erosion and help suspended particles of sediment settle to the bottom, their restoration will dramatically improve the Bay ecosystem.
More information about underwater grass abundance in the Chesapeake Bay can be found in a report from the Virginia Institute of Marine Science (VIMS).