Eelgrass

The importance of eelgrass

Eelgrass (Zostera marina L.) is the dominant species of seagrass found in the Great Bay Estuary and is a cornerstone species of healthy estuaries, including our own Great Bay Estuary. It grows in underwater meadows, helping to stabilize sediments in the seafloor and provide homes for fish and shellfish (like crabs, lobsters, and more). It also filters nutrients and sediments, improving water quality. Eelgrass provides resilience functions like capturing and storing carbon and reducing wave energy.

But eelgrass has been in decline for decades across New England, including in our Great Bay Estuary. In New Hampshire, we have significant eelgrass acreage over the last few decades as a result of stressors including poor water quality. Multiple factors influence eelgrass health, including nitrogen, stormwater runoff, temperature, precipitation, light, sediment, as well as legacy impacts (like pollution from decades ago).

Due to its importance for our estuarine ecosystem, PREP and our partners have been involved in multiple efforts to monitor and restore the extent and health of our eelgrass beds throughout the years. This webpage was created to give visitors like yourself a chance to see, understand, and experience some of our most recent work with this essential plant. Explore through the pictures, videos, and data offered here to get a glimpse of this amazing aquatic habitat that hides right below the surface!

Eelgrass Dashboard

In order to observe the changing health and conditions of eelgrass beds throughout the Great Bay Estuary, PREP started an estuary-wide eelgrass monitoring program in 2021, which we commonly refer to as “Tier 2.” As part of this annual monitoring program, we visit 25 sites throughout different zones in the estuary and take measurements of eelgrass including average canopy height, coverage, density, and biomass. Compiling that data within our Eelgrass Dashboard below, you can now see how our eelgrass is doing in Great Bay!

Use the Dashboard’s two interactive maps to explore the conditions of different sites or areas and see videos or images taken from those field visits. Then use the Compare tab to view the selection of your two maps side-by-side to see the differences across sites or years! Take a look through our quick tutorial to get started or dive right in by using the buttons below!

Dashboard Tutorial

Launch the Eelgrass Dashboard

To further explore the latest status and trends in eelgrass, be sure to check out the Eelgrass Indicator in our State of Our Estuaries report. And to see more maps of historical eelgrass extents in Great Bay, visit the Great Bay Estuary Eelgrass viewer hosted by New Hampshire Department of Environmental Services.

Eelgrass Restoration

Although we are seeing some natural eelgrass recovery in our estuary as water quality improves, it can always use a little help through direct restoration efforts. This section highlights some of the common techniques used for restoring eelgrass, as well as some of the specific projects that PREP and partners are engaged in through the Great Bay Estuary. Be sure to check in, as this section will be updated throughout the field seasons!

Restoration Techniques

PREP Eelgrass Restoration Projects

The field season is a busy time for PREP! Especially since we have started working with partners on eelgrass restoration. See below for summaries and results of the projects we have been working on.

2022 Field Season

The 2022 field season is still underway, but we are already seeing some success at the two coastal sites that were planted in early June! This year is a continuation of the work with the same partners that was started in 2021. Unlike 2021, this year’s plantings are solely done using the Horizontal Rhizome Method. A total of 1,080 shoots were harvested from a coastal donor bed and transplanted at two nearby sites selected from an updated suitability model. See the planting diagram below.

While beds in the Great Bay did not appear dense enough for harvesting in the spring, they have recovered nicely over the summer, and therefore the project team is scheduled for a fall harvesting and planting in the Bay. Be sure to check back in for the results!

And we have a fun video for you… We didn’t know the GoPro was filming. (Whoops!) Go watch Dave, Sierra, Trevor, and Lauren (our cameraperson) planting a site at the mouth of the Sagamore Creek below.

2021 Field Season

In 2021, PREP partnered with local eelgrass scientists and practitioners – Dr. David Burdick from the University of New Hampshire and Dr. Alyssa Novak from Boston University, staff from the Great Bay National Estuarine Research Reserve and The Nature Conservancy, and the Great Bay-Piscataqua Waterkeeper – to start planting experimental eelgrass beds around the Estuary.

The project team and a host of volunteers transplanted a total of 8,500 eelgrass shoots across five sites in the Great Bay Estuary. Sites were specifically selected using results from an updated suitability model identifying locations of high potential for eelgrass recovery. Shoots were harvested from two donor beds and transplanted using two different techniques: TERFs and Horizontal Rhizome Method (see “Restoration Techniques” above for more information). Often with the help of student volunteers, these sites were periodically monitored using snorkel and video equipment throughout the summer and fall of 2021 (see the video below).

Unfortunately, likely due to both significant amounts of macroalgae and record amounts of rainfall throughout July, only a minimal amount of shoot survival was observed at one site in Southern Great Bay.