Bay Grasses (Submerged Aquatic Vegetation)

Coverage and Habitat Status of Submerged Aquatic Vegetation (SAV)

The abundance of bay grass in Chesapeake Bay has fluctuated greatly since the Virginia Institute of Marine Science (VIMS) started mapping the resource in 1984. The following is a bulleted timeline of events that have affected the growth of bay grasses over the last century.

  • Eelgrass, the most widely distributed species in the bay, was nearly decimated by “wasting disease” in the early 1930’s.
  • Despite significant increases in bay grass numbers by the 1940’s, introduction of exotic species such as water chestnut and Eurasian watermilfoil displaced many native bay grasses.
  • Mute swans reproduced rapidly and began feeding on bay grasses after their introduction in 1962.
  • Tropical Storm Agnes (1972) caused widespread damage to bay grass beds.
  • Large scale declines in submerged aquatic vegetation in the late 60’s and early 70's due to increases in nutrients and sediments to the bay.
  • Tracking of bay grass populations by scientists began in 1978.
  • VIMS started mapping bay grasses with aerial photography in 1984.
  • In 2002, bay grasses reached record high numbers with an estimated 85,252 acres of SAV mapped bay-wide.
  • Hurricane Irene and Tropical Storm Lee (2011) significantly reduced underwater grasses in the upper part of the bay.
  • Underwater grasses reached 53,277 acres in Maryland’s portion of the Chesapeake Bay in 2015, the highest abundance ever recorded by the aerial survey.
  • In 2016, underwater grasses increased for the fourth straight year in the state’s portion of the Chesapeake Bay, reaching a record of 59,277 acres.
  • Underwater grasses reached 62,357acres in Maryland’s portion of the Chesapeake Bay in 2017, surpassing the 57,000 acre target and achieving a new record for the third consecutive year.
  • Maryland experienced record high rainfall and stream flows into the Chesapeake Bay in 2018 and 2019. This led to higher levels of nutrient and sediment pollution, poorer water clarity and record low salinities in many of Maryland’s waterways. Because of these reduced habitat conditions, underwater grass abundance declined in 2018 and again in 2019 to 39,264 acres.​
Maryland SAV Coverage Graph 

Click Here for Larger Image

​​​