Wild celery and water stargrass are thriving in the Susquehanna Flats. Photograph, Chesapeake Bay Program

Chesapeake Bay underwater grasses are celebrating an amazing recovery. For the fifth year in a row, these sentinels of clear water — several species in all, most native but some not — have increased in abundance. In 2017, grasses throughout the Chesapeake broke the 100,000-acre mark, the highest seen in several decades of monitoring.

It’s a happy twist in what has been at times an ecologically sad story. Bay grasses were once so plentiful in Maryland that marina owners would ask state officials to poison the plants so they would not foul boat propellers. But the growing population in the watershed and the resulting increases in nutrients and sediment entering the Bay, combined with these ill-informed herbicide campaigns and natural diseases, sent grasses into decline by the early 1970s.

In a greenhouse at the Appalachian Laboratory, ecologist Katia Engelhardt (above, top) propagates different species of wild celery to see how they respond to varying light conditions. Meanwhile, at the University of Maryland, College Park, geneticist Maile Neel (above, bottom) tests their genetic makeup. Photograph above top, Nicole Lehming; above bottom, Rona Kobell

Plants need nitrogen and phosphorus for growth, but too much fuels algae blooms that block the light they require. Sediment leads to turbidity in the water, which also blocks light and stops or slows growth. Stressors associated with human population growth — more impervious surfaces, more sewage, development of once open land — began the grass decline, but Tropical Storm Agnes accelerated the job in the spring of 1972. The storm, hitting at the most vulnerable juncture as plants were starting their new growth, wiped out the beds in the Susquehanna Flats and other regions of the Chesapeake. Declines persisted through the 1970s and ’80s and recovery was slow through the ’90s, making the recent recovery that much more remarkable.

Now, the question becomes: How do scientists and restoration managers sustain the recovery, which bodes well for the crabs and fish that call these areas home, and push for further restoration efforts to help nature along? Two scientists are working on an answer.

Vallisneria americana, also known as wild celery, has become a power house among the species of grasses that grow in the Chesapeake. A Frostburg ecologist and a College Park plant geneticist are looking at the genetic diversity of the plant, and hoping what they have learned will help fuel the continuing recovery of these essential plants in the estuary. The takeaway is that water-quality improvements need to continue for grasses to keep on rebounding.

“The big message, and we need to hit it hard, is that it’s mostly about water quality,” said Maile Neel, the plant geneticist at the University of Maryland, College Park who is working on the project with the Appalachian Laboratory’s Katia Engelhardt. Given the levels of genetic diversity that have been found, if water quality continues to improve, then the species should thrive, Neel said.

In 2017, the Chesapeake Bay contained almost 105,000 acres of underwater grasses total, more than halfway to its ultimate restoration goal of 185,000 acres. The highest percentage of increases in grass levels occurred in the tidal fresh parts of the Chesapeake, where wild celery thrives. The grass helped the region reach 96 percent of its acreage goal.

Its resilience led to questions that Neel and Engelhardt hoped to be able to answer. Given the decades-long declines in the species, scientists had concerns that genetic diversity could be too low to promote resilience. Many assumed that this species rarely reproduced by seed. Without sexual reproduction, many shoots that look like separate plants when viewed from above would actually be the same individual.

Katia Engelhardt uses shade cloth (above top) to mimic changes in light levels in the Bay due to different levels of water clarity. The lighter shade cloth on the left allows some light through to the plants below, while the right blocks most of the light. She is finding that some individuals can persist with most of the light blocked, whereas others do not. DNR biologist Brooke Landry (above bottom), who chairs the Chesapeake Bay Program’s SAV Workgroup, stands with colleague Becky Golden. Photograph, above top, Nicole Lehming; above bottom, courtesy of Brooke Landry

Along with their students, Neel and Engelhardt collected plants from a variety of areas in the Bay and its watershed including the Susquehanna Flats, the mainstem of the Potomac, the Baltimore tributaries, and the non-tidal Potomac north of Great Falls. Neel’s team extracted the DNA from approximately two-centimeter pieces of leaf from each sample and ran genetic tests to determine how many varieties of the plant existed. To date, they have analyzed 3,771 samples of wild celery from locations that represent different growing conditions.

They have determined that most populations of wild celery in the Chesapeake are made up of many genetically different individuals, which bodes well for the long-term survival of the species as well as for restoration efforts. The only exception to this pattern is in the Potomac River upstream of Great Falls where two types of plants dominate over hundreds of kilometers of the river. They found genetic differences among populations in the Bay that indicate three different regions in which populations share genetic information. The scientists regularly discuss their findings with Brooke Landry, a biologist with the Maryland Department of Natural Resources, who also heads the Chesapeake Bay Program’s SAV (submerged aquatic vegetation) Workgroup, and others who work on SAV restoration efforts.

Simultaneously, Engelhardt has grown selected individuals, identified genetically by Neel, in a greenhouse. She is conducting experiments to determine how the genetic diversity at the individual, local, and regional scales affect the species’ ecology. These experiments have revealed that productivity increases when plants with similar genetics, or “genotypes,” are planted together, and that different genotypes have different growth patterns.

Algae that thrive on nitrogen and phosphorus, along with floating sediment particles, can block light and prevent plant growth. In experiments using shade cloth to mimic changes in light levels in the Bay due to different levels of water clarity, Engelhardt has determined that conditions in which plants could grow in the wild vary across genotypes. She is finding that some individuals can persist with most of the light blocked, whereas others do not.

Discovering the genetic diversity and range of wild celery has led to changes in how the Chesapeake Bay community restores grasses. In addition to state-sponsored restoration efforts, the Chesapeake Bay Foundation and some watershed organizations run re-seeding programs across the watershed. Now, restoration managers are calling Neel and Engelhardt for advice, and the scientists are telling them to group genetically similar grasses in places where they’re known to grow well instead of assuming all the seeds are alike and dispersing randomly.

“She (Neel) has convinced us that we need to keep our seeds in the same region that they were harvested from,” Landry said. “Her argument is that it’s best to keep the plants local. It might be a waste of seeds and time if we move them too far — they might not be genetically suitable for the conditions in that spot. Plus, since they’ve found so much genetic diversity in the wild celery populations in the Bay, there’s no need to move the plants outside their region to increase diversity.”

Maryland and Virginia have made some efforts to restore the beds by planting mostly eelgrass in the southern portion of the estuary, but many of those efforts were not successful long-term. Wild celery restoration efforts are relatively recent. Neel, Engelhardt, and Landry are hopeful they will be more resilient.

“Restoration managers paid a lot of attention to habitat requirements for the different species of grasses,” Neel said. “But they were not paying attention to genetic diversity within species because they didn’t know anything about it.”

Engelhardt agreed. “Prior to Maile’s and my work,” she said, “there really was no thought to where people were putting things.”

Bay grass recovery is the result of decades of dedication. Neel and Engelhardt’s work indicates excellent prospects for continued recovery and resilience.

—kobell@mdsg.umd.edu