Seagrass, for all its benefits, is not the most glamorous of ocean life. The underwater wisps, in varied shades of green, grow in shallow, sunlit water along coastlines. In time, they can mature into dense meadows, supporting a wide array of life—baby fish, crabs, worms, anemones, and all that eat them, including birds. Mostly, though, seagrasses are overlooked and forgotten, out of sight and mind, even as they decline by 7 percent globally year after year.
In the Chesapeake Bay, however, seagrasses have scientists sitting up and taking notice. That’s because, for the first time in decades, submerged aquatic vegetation (SAV, in scientific parlance) is returning. A century’s worth of fertilizers washed into the bay killed most of the grass by the 1980s, and for decades scientists have tried to reduce pollution, with little success. But now, after the U.S. Environmental Protect Agency (EPA) spearheaded a new effort in 2010, seagrass is back. A recent paper, published in Proceedings of the National Academy of Sciences, found a remarkable turnaround in the grass’s growth after the bay’s nitrogen concentration dropped by 23 percent.
“[SAV] is the most easily visible indicator of water quality,” says paper author Brooke Landry, a biologist with the Maryland Department of Natural Resources and chair of the Chesapeake Bay Program's SAV Workgroup. “We’ve been surveying [SAV] since 1984. Over that 30-year time period, there’s been an increasing trend.” Today, there is more SAV in the bay than there’s been in a half-century; it regained over 40,000 acres since surveys began, according to the new research.
The turnaround has scientists feeling hopeful about the bay’s future, some for the first time in their careers. “This is maybe the first [year] where I feel comfortable being a little bit positive,” says Tom Horton, a professor at Salisbury University who’s researched the Chesapeake’s health for 30 years. “It takes a lot of confidence to say what they're saying.”
Because seagrass supports a rich food web, theoretically its regrowth should support more wildlife, including waterbirds, in the bay. While experts hesitate to definitively link seagrass health to bird populations, they have seen encouraging trends. Bill Harvey, a game bird biologist with the Maryland Department of Natural Resources, has conducted an annual survey of Chesapeake Bay bird populations since 1990. As the grass recovered, he watched some waterbird populations soar, too.
“When I first started, there weren’t many birds, nor was there much SAV,” Harvey says. “It's really improved here in recent years. The most common species that's almost certainly related to the SAV is the Tundra Swan.” These birds have gone from a low of 8,200 wintering birds in 2006 to numbering more than 16,000 in 2018. Redhead ducks have had an even more dramatic recovery, growing from around 900 individuals in the mid-1980s to around 30,000 this year.
“That's almost certainly due to the SAV,” Harvey says. Both Tundra Swans and Redhead ducks feed on seagrass directly.
The seagrass also nurtures populations of crabs and molluscs, which are important foods for birds. For instance, American Black Ducks eat snails that live in the underwater meadows, making SAV an important wintering habitat for the species.
These birds, unfortunately, are one of several species whose numbers have declined in recent years. Once the most abundant dabbling duck in the United States, only around 40,000 individuals now winter in the bay, according to Harvey’s survey. The counts show that a number of other birds are in similar straits, including goldeneyes, Ring-Necked Ducks, and Green-Winged Teals. All of these birds eat plants (like SAV) and the molluscs they support, so there’s cause for hope—but maybe not for a few more years.
“It might take [more] time,” says Alicia Berlin, a research biologist with the U.S. Geological Survey who studies American Black Ducks in the Chesapeake Bay. “There might be other influences. For example, they might be limited by something on their breeding grounds.” The American Black Duck, in particular, is easily disturbed by people, she says, and might be affected by noisy boats and development.
Bryan Watts, director of the Center for Conservation Biology at the College of William & Mary in Virginia, declined to tie birds’ recovery directly to SAV. “We wouldn't typically experience direct effects on the birds, but indirectly, based on the ecosystem improving,” he says. But he still maintains that regulating and reducing pollution, including pesticides
such as DDT, has been critical for birds of the Chesapeake.
Though researchers might disagree about what role seagrass plays in the increasing bird numbers, it’s clear that the bay’s health is improving, and that’s a win for birds. However, the scientists’ enthusiasm is tarnished by challenges on the horizon—namely, climate change. Already, they’ve noticed the bay’s seagrasses changing as the water warms, potentially reversing some of the recent gains.
“There has been some recovery of the eelgrass in the last few years, but eelgrass is one of the plants that we're most concerned about because of climate change,” Landry says. “The temperatures in the bay have increased, and it's a cold-water plant. It doesn't do well with thermal stress. As we heat up, we've already seen a big dieback of eelgrass in the bay.”
Climate change could also raise water levels, flooding marshes and removing critical habitat for wildlife. Increased rainfall could also flush more pollutants and sediment into the bay, potentially reversing any recent progress on water quality.
The majority of the positive changes in the bay happened following President Obama’s 2009 executive order, which recognized the Chesapeake Bay as a national treasure and empowered the EPA to set limits for pollutants in each state. President Trump has repeatedly threatened to pull funding for the EPA’s Chesapeake Bay restoration, but so far has not succeeded.
He has succeeded, however, in reversing EPA programs to reduce carbon emissions, which cause climate change and sea level rise. “If we don't get a handle on climate change, if we really do get six or seven feet of rise by the end of the century or more—holy crap,” Horton says.
Still, he’s trying to stay positive.
“I think we've got all of the pieces of the puzzle on the board,” Horton says. “It’s a matter of money and political will and how well we're going to apply them.”