Just as coral reefs are to tropical waters and rainforests are to the Amazon, seagrass meadows are important to the New England coastline. They provide habitat and foraging grounds for marine animals, buffer the shoreline from erosion, filter the water, and oxygenate the sediments. Eelgrass (Zostera marina), an underwater flowering perennial plant, is the predominant seagrass species in Massachusetts and can be found growing in many of our bays, harbors, and open-water shelves. Eelgrass beds can be dense meadows or patchy mosaics, both providing critical refuge and habitat for recreational and commercial fisheries species including flounders, scallops, lobsters, tautog, and black sea bass. Studies have found that fish abundance, biomass, and species richness rise with increasing eelgrass meadow complexity, so more eelgrass may mean stronger fisheries, making eelgrass a highly valuable resource. In fact, one study valued seagrass meadows, based on the ecosystem services they provide and their support of commercial and recreational fisheries species, at $50,000 (in 1994 USD) per acre, per year, globally. That’s close to $100,000 per acre, per year in today’s dollars.
Despite their ecological value, seagrasses are considered among the most threatened ecosystems on earth. Researchers estimate a 7% mean annual rate of decline globally since 1990. Massachusetts has had a long history of persistent eelgrass meadows, however, from 1996 to 2006, eelgrass has declined in the state at a mean rate of 4% per year – that’s 1,866 acres of eelgrass lost from 30 Massachusetts embayments.
The main threat to eelgrass is poor water quality, which reduces the light available to plants and in some cases results in a low oxygen, toxic environment in the sediments. Declining water quality in Massachusetts is mostly due to nitrogen loading via septic tanks and fertilizers, and stormwater runoff from impervious surfaces (i.e., buildings and parking lots). Eelgrass damage and loss can also result from coastal construction projects, such as dredging and dock building, common boating and fishing practices, such as anchoring, mooring chain scour, propellers running in shallow water, and some bottom-tending fishing gears.
Due to its importance as a fisheries habitat, MarineFisheries has been working to restore, monitor, and reduce impacts to eelgrass throughout Massachusetts waters. Since 2004, MarineFisheries has successfully restored seven acres of eelgrass through transplants from healthy donor beds into areas deemed suitable for restoration. Five acres planted around the Boston Harbor Islands from 2004 to 2007 have expanded to encompass greater than 10 acres in 2013. Because it takes 3 to 5 years for a successfully transplanted eelgrass bed to grow and become functionally equivalent to natural eelgrass meadows, we will continue monitoring our recently planted grass to ensure that the restoration sites are on a trajectory of development. Despite these highlighted successes, many attempts at planting fail, due mostly to poor site selection – if eelgrass isn’t already growing somewhere due to site conditions, the site may not be amenable to transplant establishment.
Restoration is time-consuming and costly – ranging from $250,000 to $350,000 for site selection, planting, monitoring, and where necessary, re-planting – and not always effective at replacing lost habitat. For this reason, MarineFisheries is also focusing on ways to protect and reduce impacts to eelgrass. Conventional boat moorings scour eelgrass and leave large circular scars. Working with municipalities, MarineFisheries is helping to install and monitor moorings that have a flexible, floating chain that does not drag on the bottom.
We are also working to better understand how changes in eelgrass meadows relate to changes in our environment, including climate and storm influence, as well as human impacts, including fishing gear interactions. To answer these questions, we gather high resolution data at transects in a large eelgrass meadow along the Beverly coastline quarterly. This monitoring program is part of a global seagrass monitoring network called SeagrassNet. SeagrassNet stations around the world are collecting comparable data which can be used to assess global trends. Overall, our data show a 56% decline in eelgrass biomass and 51% decline in density since 2008 at the Beverly SeagrassNet stations.
Today Massachusetts has approximately 30,000 acres of eelgrass remaining. This is a far cry from the estimated hundreds of thousands of acres present in pre-colonial times. It’s up to us to be stewards of this valuable fisheries habitat and to work toward curbing its decline. For more information about eelgrass and what you can do to minimize your impacts, please visit our website at http://www.mass.gov/eea/agencies/dfg/dmf/programs-and-projects/seagrass.html and blog http://seagrasssoundings.blogspot.com/
American lobster finding shelter in a dense eelgrass meadow in Manchester outer harbor.
Divers plant eelgrass disks in Salem Sound.
The disks act as an artificial root matrix to hold the plants until they establish themselves. This method was developed by researchers at the Cornell Cooperative Extension.
Regulations in red are new this year.
Purple text indicates an important note.