Overwhelmed by record high flows and warm temperatures, the Chesapeake Bay’s vast underwater meadows last year suffered their largest drop since surveys began, with acreage plummeting at least 33% from 2018.It's good to have goals. I try not to get too excited about losses and gains of seagrass from year to year, as it is always tied to some weather event. Some enterprising scientist should try to invent a metric for seagrass that was not weather dependent. It shouldn't be that hard. Statistical methods are pretty good these days.
But the declines were not uniform throughout the Bay. Underwater grass beds in many fresh and low-salinity areas of the Chesapeake and its tidal tributaries held their own, while beds in mid– and high-salinity areas suffered the brunt of the impact.
“We see a lot of little losses in a lot of places, and little gains in a lot of places,” said Christopher Patrick, assistant professor of biology at the Virginia Institute of Marine Science, which conducts the annual aerial survey of the Bay’s grass beds. “And then we’ve had a couple places that just had a really bad year.”
The Bay lost a bit more than 34,986 acres of submerged aquatic vegetation, or SAV, erasing nearly a third of the plants from the shallow waters around the Bay.
The loss was probably larger, scientists say, but it wasn’t fully documented: Bad weather kept them from completing the survey in 2018.
The 66,387 acres of Bay grasses mapped last year represented just 35.9% of the Bay Program restoration goal of 185,000 acres.
Maryland DNR was more sanguine: Maryland’s Underwater Grasses Resilient Against Severe Rainfall
The Maryland Department of Natural Resources reports a second consecutive year of underwater grass loss in certain portions of the Chesapeake Bay in 2019 due to record high rainfall and stream flows into the bay. Some areas of Maryland’s portion of the bay, however, have shown improvements. During the annual survey, 39,151 acres of underwater grasses were mapped in Maryland, representing 49% of the state’s 2025 restoration target and 34% of its ultimate restoration goal of 114,065 acres.
While this is a decline from the record-high 62,357 acres of underwater grasses mapped in 2017, it was not unexpected. The high rainfall and stream flows into the Chesapeake Bay in 2018 and 2019 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.
Last year’s flows were even higher than those from Hurricane Agnes, which completely wiped out grasses in the upper Chesapeake Bay in 1972. The diversity of grasses present in the upper bay and tributaries makes those areas more resilient to stressors like the high flows observed in 2018 and 2019.