Encouraging news for underwater weeds in Chesapeake Bay, despite 'mysterious' losses around gunpowder and central rivers – W&M News

Encouraging news for underwater weeds in Chesapeake Bay, despite 'mysterious' losses around gunpowder and central rivers – W&M News

An annual survey by researchers from VIMS has mapped 76,462 acres of underwater grasses in the Chesapeake Bay and its tributaries in 2022.

Their report documents a 12% increase in submerged aquatic plants in the areas the team mapped, with lead researcher Christopher Patrick, director of the VIMS SAV Monitoring and Restoration Program and associate professor of biology, noting that “for the most part, we have had a really encouraging year for SAV throughout the Gulf.”

Underwater bay grasses are a vital part of the bay's ecosystem. They provide habitat and nursery grounds for fish and blue crabs, serve as food for animals such as turtles and waterfowl, filter water by reducing wave action, absorb excess nutrients and reduce beach erosion. VIMS tracks the abundance of underwater grasses as an indicator of the bay's health for the Chesapeake Bay Program, a federal-state partnership established in 1983 to monitor and restore the bay's ecosystem. Using aerial surveys conducted from late spring to early fall each year, VIMS researchers estimate the extent of underwater grasses present in the bay.

Trends in salty and fresh areas

The VIMS team continued its practice — first introduced in 2013 — of classifying abundance using four different salinity zones, which are home to underwater grass communities that respond similarly to storms, drought, and other growth conditions.

Some trends emerged across salinity zones. Saline areas have continued to regain ground lost in the 2019 collapse, with both eelgrass and wedgegrass expanding.

Patrick attributed this to ongoing nutrient management efforts and the cool summers associated with the La Niña phenomenon. He pointed out that “the real test for these areas will be the summer of 2024 when hot summer temperatures, a known stress factor for eelgrass, return with the expected El Niño cycle.”

The research team will evaluate these impacts, if they occur, in the spring of 2025. Weeds in freshwater areas have remained roughly constant, with some areas within the region exceeding investigation targets.

Between 2021 and 2022:

  • Abundance of Gulf grass in the fresh waters of the Gulf ( Freshwater intertidal zone) decreased 73 acres (from 19,179 acres to 19,106 acres).
  • Abundance of bay grass in the slightly salty waters of the bay ( Low salinity area) decreased 1,239 acres (from 8,384 acres to 7,145 acres).
  • Abundance of Gulf grass in brackish Gulf waters ( Mesohaline salinity zone) An increase of 6,841 acres (from 24,091 acres to 30,932 acres).
  • Abundance of Gulf grass in the highly saline Gulf waters ( Polychromatic salinity zone) increased 2,829 acres (from 16,371 acres to 19,200 acres).

Dive deeper: Losses in the brackish salinity zone

In 2022, there was a significant local decline of more than 40% around the Gunpowder and Middle Rivers, which are part of the brackish oligosalinity zone.

According to Patrick, “Given that this loss was local and did not affect parts of the West Shore to the north, it was likely caused by something happening in the Gunpowder River watershed.

“We have noticed some significant spikes in turbidity in the spring in that area that may have something to do with the decline. Ultimately, it is something that requires further investigation to determine the cause to ensure this does not happen again in the future.”

If not for the mysterious losses around the Gunpowder River and Middle River, the 2022 report would have recorded a significant 18% increase in SAV prevalence in the Chesapeake Bay.

Local highlights

The abundance of underwater grass can vary from one species to another and from one river to another. In 2022, other local highlights included:

  • Gunpowder and central rivers: Nearly 1,500 acres of underwater grass were lost in the Gunpower and Central Rivers (more than 40%), representing 15% of the loss seen in the Oligohaline area of ​​the bay (a slightly saline area). The reasons for the large losses seen in this small area are unknown and require further investigation by Gulf scientists.
  • Susquehanna Apartments: There has been a resurgence of submarine grass on the Susquehanna Flats over the past several years, and in 2022, the strip has gained another few hundred acres.
  • Voice of Tangier: The Maryland and Virginia portion of the Tangier Strait gained thousands of acres of underwater grass, an increase of 54%. These healthy grass flats will serve as high-quality blue crab habitat, which is good news for the crabs that work around Smith and Tangier Islands.
  • Mobjack Bay to Poquoson Flats: The area of ​​Mobjack Bay to Poquoson Flats, an area of ​​the bay dominated by eelgrass and widgeon grass, increased by 27%. Underwater grass abundance is close to reaching its highest level since 1997.
  • Pocomoke River: The lower Pocomoke River in Virginia rose 32%, while the middle and upper portion of the river remained steady.

For a closer look at the abundance of underwater weeds, you can access the results from the VIMS website. For full details, visit the SAV Monitoring and Recovery Program.

Editor's Note: Water is one of four core initiatives in W&M's Vision 2026 strategic plan. Visit the Vision 2026 website to learn more.

VIMS staff and Jake Solst, Chesapeake Bay Program

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