The Chesapeake’s underwater grasses — critical havens for everything from blue crabs to waterfowl — surged to a new record high last year, surpassing 100,000 acres for the first time in recent history.
“I never thought we would ever see that,” said Bob Orth, a researcher with the Virginia Institute of Marine Science who has overseen the annual Baywide underwater grass survey since it began in 1984. “But things are changing.”
It was the third straight year that acreage of these underwater meadows has set a new Baywide record.
The 2017 survey results, released in late April, came on the heels of a scientific study published in March that credited nutrient reductions in the Bay for a sustained long-term comeback of the grasses over the last three decades — even as those habitats are in decline globally.
“Seeing record growth in underwater grasses for the past three years just reinforces that our efforts to restore the Chesapeake Bay and its local tributaries is working,” said Jim Edward, acting director of the state-federal Bay Program partnership.
The need to restore underwater grasses is one reason that the Bay cleanup effort aims to reduce nutrient and sediment pollution, as water clouded by sediment or nutrient-fueled algae blooms can be lethal to the nearly two dozen species of underwater grasses found in the Bay.
Like all green plants, submerged grasses need sunlight to survive, and they receive more sunlight through clear water. Because of the link to water clarity, the status of submerged aquatic vegetation — or SAV — is considered a key indicator of the Bay’s health.
Grass beds are also a critical component of the Bay ecosystem in their own right. In addition to providing food for waterfowl and shelter for fish and crabs, they also pump oxygen into the water, trap sediment and buffer shorelines from the erosive impact of waves.
Overall, results from the 2017 survey showed that the Bay had 104,843 acres of underwater grasses, a 5 percent increase from the previous year. That exceeds an interim 2017 goal of 90,000 acres, and was 57 percent of the ultimate 185,000-acre Baywide goal for 2025.
When the survey began in 1984, fewer than 40,000 acres of SAV were observed in the Bay. Since then, the total amount has generally increased, though the amount in a given year may fluctuate widely depending on the weather: Big storms drive huge amounts of nutrients and sediment into the Bay that tend to cause significant losses, while very hot summers cause die-offs of eelgrass, a dominant species in high-salinity areas of the Lower Bay.
Most recently, Hurricane Irene and Tropical Storm Lee in late summer 2011 knocked grasses back to 48,195 acres in the 2012 survey, a recent low.
But after that, the beds continued their long-term recovery, with Baywide coverage increasing for five consecutive years — the longest period of uninterrupted expansion in the history of the survey — and setting records in the last three.
“There have up and downs in places, but the overall picture since 2012 has been up, up, up,” Orth said. “It’s not going down.”
The recent paper published in the Proceedings of the National Academy of Sciences, written by a team of 14 scientists, credited the overall recovery to improved water quality stemming from a 23 percent decline in nitrogen concentrations in the Bay and an 8 percent decline in phosphorus since the mid-1980s.
“We don’t need miracles,” said Brooke Landry, a biologist with the Maryland Department of Natural Resources and chair of the Bay Program SAV Workgroup and, along with Orth, one of the co-authors of the paper. “We just need a sustained effort.”
Environmental advocates said the underwater grass record was evidence that cleanup efforts are working — and need to be maintained.
“Pollution is going down, the dead zone is getting smaller, and oysters are making a recovery. This progress is extraordinary,” said Beth McGee, a scientist with the Chesapeake Bay Foundation. "But the recovery is fragile and proposed rollbacks to federal environmental protection regulations threaten future progress.”
Good news last year was heralded at the top of the Bay, where underwater grass beds in the Susquehanna Flats, historically a critical waterfowl habitat, continued their comeback after being halved in the wake of Irene and Lee. They reached 9,084 acres last year, about three-quarters of their level before those storms.
It is no longer the area of the Bay with the most grass, though. That honor goes to a huge 21,507 acre expanse of underwater grasses that extend from near Tangier Island to the Honga River, along the Eastern Shore.
Closer to the mouth of the Bay, beds have stabilized after a heat-wave caused a dieback of temperature-sensitive eelgrass beds — important habitats for juvenile blue crabs — in 2012. “It looks like eelgrass is basically stabilizing, with some increases,” Orth said. Eelgrass is of particular concern as it is one of the two primary species found in high-salinity areas; the other is widgeon grass.
Grasses are also turning up in places where they haven’t been seen in decades — if ever. In the York River, Orth said he hasn’t seen underwater grasses above Gloucester Point, near the mouth of the river, since 1972.
But last year “we found a very substantial bed of widgeon grass up there. It’s the first time ever in the survey that we saw any grass above Gloucester Point,” Orth said.
A large widgeon grass bed also popped up in the Patuxent River outside the Chesapeake Biological Lab in Solomons, MD, where it had not been previously mapped.
Although the overall trend is upward, the magnitude of the changes from 2016 to 2017 varied by salinity zone, each of which hosts a slightly different mix of grass species:
- In the tidal fresh zone, at the head of the Bay and in the uppermost tidal reaches of most tributaries, underwater grass beds increased by 2,462 acres to 19,880 acres, a 14.1 percent increase and 96.5 percent of the goal for that area.
- The slightly salty oligohaline zone that occupies a relatively small portion of the Upper Bay and tidal tributaries, lost 190 acres, dropping to 8,398 acres, a 2.2 percent decrease. That is 81.3 percent of the goal for that area.
- The moderately salty mesohaline zone — the largest area of underwater grass habitat, stretching from near Baltimore south to the Rappahannock River and Tangier Island and including large sections of most tidal rivers — had the greatest increase, gaining 4,140 acres to 61,331 acres, an increase of 7.2 percent. That is 51 percent of the goal for that region.
- The very salty polyhaline zone — from the mouth of the Rappahannock and Tangier Island south, including the lower York and James rivers — increased 763 acres, to 15,234 acres, an increase of 5.3 percent.
While grass beds are expanding or holding their own in much of the Bay, much of the recovery hinges on the mesohaline zone in the midsection of the Bay. Widgeon grass is by far the dominant species there, and its acreage has nearly tripled in just the last five years, from less than 20,000 acres in 2010 to more than 57,000 acres last year. But widgeon grass is notorious for its boom and bust cycles, as it can disappear quickly if conditions turn bad.
In 2003, that area lost half of its underwater grass coverage after severe storms muddied the waters.
But, Orth said, widgeon grass likes warm water and might be benefitting from gradually warming Bay temperatures. In the event of another setback, he said, those beds may be better poised for a comeback than in the past because they have become so large and dense, and are producing prodigious amounts of seeds.
Also, Landry said inspections of some beds last year showed that, in some places, other species are starting to appear along with widgeon grass, giving beds diversity that could help them better withstand severe events.
“I think these plants can withstand bad weather and storm events and things like that if the system itself is healthy,” she said. “So if we keep up with our nutrient reduction plans and our sediment reduction plans, and we set the stage for a thriving environment, these beds will be more likely to withstand stressful events. They can’t withstand long-term chronic stress.”