Published September 4, 2026 | by Amy Sauber, PREP Communication Coordinator
Harvesting eelgrass seeds to help our struggling Great Bay meadows is a profoundly hopeful effort.
Picture a sunny, hot, summer day. A community of local volunteers and PREP staff wade into cold water, clad in wet suits and snorkel gear. They carry bright orange netted bags that (within the hour) will hold harvested eelgrass seeds and flowers. In waist deep water, they find themselves in an underwater meadow. They mask up and dip their heads below the surface. Verdant, vibrant, and full of wildlife. Schools of fish, crabs, and lobster. Sunlight pours over the meadow, shimmering in synch with the gentle wave action over their heads. They begin their work.
This was an actual scene from PREP's seed-based eelgrass restoration effort in the Great Bay Estuary, a method we've brought to New Hampshire for the first time. Trevor Mattera, PREP’s Habitat Restoration and Water Quality Program Manager, leads the project which is supported by funding from a small family foundation.
“I've done a lot of fieldwork throughout my career,” Trevor says. “I can honestly say that not much beats snorkeling through lush eelgrass meadows on a beautiful August morning with a team of volunteers picking eelgrass flowers. It really is amazing.”
Eelgrass (Zostera marina) is the dominant species of seagrass found in the Great Bay Estuary. It is a rooted, flowering plant (not seaweed), and it grows in underwater meadows, helping to stabilize the seafloor and provide homes for fish and shellfish. It also filters nutrients and sediments, improving water quality. To boot, it also sequesters carbon.
Because eelgrass is a critical habitat and indicator of water quality, PREP has monitored its presence and health in the Great Bay Estuary for decades and actively works on eelgrass restoration projects to help existing meadows become healthier.
Eelgrass Decline in the Great Bay Estuary
Due to a number of complex factors, eelgrass has been in decline for decades across New England, including in our Great Bay Estuary. The Great Bay Estuary starts at the mouth of the Piscataqua River and the coast of Kittery, Maine and moves inland toward Great Bay, a large bay south of Adam’s Point in Durham, New Hampshire.
While coastal meadows near and around Portsmouth Harbor and Kittery are thriving, eelgreass within Great Bay proper recently experienced a significant decline. The importance of supporting these habitats has come to a critical moment.
We know from over thirty years’ worth of data that there are multiple drivers that influence eelgrass health for better or worse in our estuary. Factors include nitrogen, stormwater runoff, temperature, precipitation, light, sediment (often re-suspended sediment), as well as legacy impacts (like pollution from decades ago). Generally speaking, eelgrass in our estuary thrives when conditions include colder, clearer water, and with less runoff inputs.
Eelgrass Restoration Methods
As these estuarine meadows struggle, restoration methods can help jump-start their recovery. Eelgrass reproduces in two ways: through rhizomes and through seeds. These methods also lend themselves to restoration strategies.
To use an analogy, many familiar garden plants have rhizomes. If you divide and transplant part of a rhizome elsewhere, you can grow a new plant (essentially a clone of your original). One method of eelgrass restoration works in much the same way. Technicians harvest healthy eelgrass plants and their rhizomes from underwater donor meadows and transplant them where eelgrass has declined.
Seeds offer a different approach.
Unlike rhizome-based transplants, seeds contain genetic material from two parent plants. This means seed-based restoration can introduce greater genetic diversity to a meadow, potentially supporting that meadow's ability to respond to restoration and/or adapt to changing conditions.
Many areas in New England are now focusing efforts on seeds-based eelgrass restoration, as they've been proven successful in other regions.
The reproductive part of an eelgrass shoot, featuring the formation of grain-of-rice sized seeds.
The Power of 250,000 Seeds
Since 2020, PREP and partners have led rhizome-based restoration efforts, including a half-acre transplant planting. This method is costly and challenging to scale. It has also offered varying degrees of success on a year-by-year basis. Now that more research is available on seed-based projects, PREP has switched its approach.
“This project really sets the groundwork for a dedicated program for large-scale eelgrass restoration here in Great Bay,” Trevor says. “We're out here learning from our partners in other states, engaging volunteers and the public, and of course, planting eelgrass.”
Seed-based restoration is also easier to implement because it is less labor-intensive. Instead of harvesting entire plants and transplanting them, technicians only need to harvest the reproductive part of the plant (the part that flowers and produces seeds).
PREP has a goal of harvesting, processing, and planting 250,000 eelgrass seeds in 2026.
A special thank you to our snorkel volunteers that supported this important work: Kim Arlen, Dave Burdick, Suzannah Buzzell, Brianna Group, Grant and Jonathan McKown, Melissa Paly, Severn Sienkiewicz, and Lauren White.
Collaboration with Volunteers and Partners
Aside from genetic benefits, PREP's seed-based restoration project is also well-suited for hands-on community involvement. To collect seeds, we established snorkel and SCUBA dive operations in Portsmouth Harbor. This August, PREP staff and an incredible group of volunteers visited coastal donor beds near Fort Foster (Kittery, ME) and New Castle Beach (New Castle, NH).
Our SCUBA team has also collected eelgrass shoots in deeper underwater meadows off the coast of Fort Foster.
The health of these thriving meadows may support the recovery of the depleted meadows in Great Bay proper.
Volunteers Grant and Jonathan McKown hold up over 300 harvested eelgrass reproductive shoots.
What Happens After Seed Collection
After collection, reproductive shoots are held in flowing seawater tanks at the University of New Hampshire’s Jackson Estuarine Lab. PREP is a local organization and National Estuary Program housed at the University's School of Marine Science and Ocean Engineering.
The tanks replicate the coastal meadows where they were harvested. Here, seeds from the shoots will continue to mature. Eventually, they will separate from the shoot and settle at the bottom of the tanks.
This process mimics how eelgrass seeds naturally release and settle on the seafloor.
Once they’re at the bottom of the tank, our team will collect each seed, which is approximately the size of a grain of rice.
PREP's Trevor Mattera and Addie Coletti add harvested eelgrass plants to tanks at Jackson Estuarine Lab
In September, PREP will engage students and volunteers throughout the process to clean and process the seeds. In October, we’ll visit select restoration sites, including Great Bay proper, where we’ll seed existing meadows.
Seeding is simple! In fact, it looks a lot like sowing seeds on land, except in the water. At specific restoration sites in Great Bay, we will toss the seeds and let the seeds settle to the seafloor.
The project also includes a technology-transfer visit to Cornell Cooperative Extension’s Eelgrass Program on Long Island, helping our team build a sustainable, long-term restoration program for New Hampshire and southern Maine.
As we continue this work into the fall, Trevor reminds us of why this work matters and the hope we hold onto as PREP continues to carry our mission:
“Eelgrass is such a foundational part of our beautiful coastal environment here in New Hampshire and throughout New England. Seeing it struggle and decline in areas where it has once thrived and supported our estuarine ecosystem for centuries is troubling. But it has been empowering working with such a committed and passionate network of scientists, professionals, volunteers, and communities to help its recovery."
