Photos of the Long Island Sound

Research & Monitoring

Status & Trends

LISS Ecosystem Targets and Supporting Indicators

Eelgrass Extent

Restore and maintain an additional 2,000 acres of eelgrass by 2035 from a 2012 baseline of 2,061.

( Click labels in legend to hide data and adjust scale )

Progress on this target will be reported in 2018 when a 2017 survey of eelgrass becomes available.

Eelgrass Abundance

Status and Trends

Meeting this target requires an average increase of 87 acres of eelgrass per year from 2012-2035. Eelgrass abundance has been assessed from 2002 to the 2012 baseline year.

The 2012 survey located 240 eelgrass beds in eastern Long Island Sound totaling 2,061 acres. An additional 80 beds of undetermined submerged aquatic vegetation (vegetation which the aerial survey was unable to conclusively identify as either eelgrass or macroalgae) totaling approximately 584 acres were also identified. Seven sub-basins had over 100 acres of eelgrass beds: Fishers Island, Quiambog Cove, Little Narragansett Bay, Niantic Bay, Mystic Harbor, Goshen Cove, and Rocky Neck State Park. The largest gains occurred in the Fishers Island and Niantic Bay sub-basins (+57 and +32 acres, respectively). Quiambog Cove and Little Narragansett Bay sub-basins experience the most losses (-19 and -15 acres, respectively). Another survey is scheduled for the summer of 2017.

While the survey was only conducted in the Eastern Basin of Long Island Sound,  eelgrass experts believe that eelgrass beds in the Central Basin are small or nonexistent while beds are absent from the Western Basin. Therefore, we use 2,061 acres as an estimated of total eelgrass coverage in the Sound, and the goal is to increase this to 4,061 acres of areal eelgrass extent as measured by aerial imagery. This target will be achieved through the successful implementation of additional water quality protections and associated reductions in land based inputs of nutrients, as well as restoration (replanting) efforts led by academic, government, and nonprofit agencies and partners.


The overall success of eelgrass is dependent on several parameters including water clarity, depth, substrate, temperature, and salinity. Many embayments where eelgrass once thrived, or could have thrived, suffer from changes to water quality and changes to substrate that now does promote the growth of eelgrass. In order to restore and enhance eelgrass beds and meet the Eelgrass Extent goal, practitioners will need to work with partners to improve water quality and substrate issues in embayments.

To date, assessment of eelgrass in Long Island Sound has occurred through aerial surveys every four to five years. Surveys have only focused on the Eastern Basin of Long Island Sound and only a few restoration projects have been successfully completed to date. In order to increase eelgrass numbers practitioners will need annual data sets on the status of the beds (aerial surveys or otherwise), a complete geographic dataset, and the greater number of restoration projects around the Sound.

How is This Target Measured?

Aerial surveys for eelgrass are conducted every few years by the National Wetlands Inventory Program (NWI) of the US Fish and Wildlife Service (USFWS) in the eastern end of Long Island Sound. The Long Island Sound Study Habitat Restoration Coordinators track eelgrass restoration projects that are in progress within the watershed by various partners and report the total acres restored annually.

To date, five aerial surveys have been conducted, with the last survey being conducted in 2017. These inventories were started because the Connecticut Department of Energy and Environmental Protection (CTDEEP) was interested in learning the status of eelgrass beds in 2001 and wanted the beds monitored periodically.

With funding from EPA, the USFWS contracted with the US Geological Survey’s l Geospatial Technical Operation Center for the collection of aerial imagery with a 0.5-1 meter resolution. Flights were conducted on June 28, 2017. The USFWS field verified habitats in September and October 2017. The data is now being analyzed, and a final report will be completed in early 2018.


Eelgrass, Zostera marina, is a rooted, underwater grass that grows along the shallow coastal waters of bays, estuaries, and beaches in the Northern Hemisphere. Eelgrass meadow habitat provides foraging areas for fish and invertebrates, and food for many migratory birds. Healthy eelgrass beds trap sediment and reduce wave energy during storms, improving water quality and protecting coastal areas from erosion.

Eelgrass bed abundance indicates good water quality and good habitat for aquatic life, and acceptable levels of nutrients. Excessive levels of nutrients such as nitrogen and phosphorous from sewage discharge and runoff can stimulate the overgrowth of phytoplankton (algal) blooms that could block the energy from the sunlight that eelgrass needs to grow.

Additional Information

Eelgrass reports:
2012 eelgrass survey
2009 eelgrass survey


Victoria O’Neill, New York Department of Environmental Conservation

Harry Yamalis, CTDEEP

Source of Data

US Fish and Wildlife Service


Data Notes

  • The technical explanation on how the target was selected is found in Appendix B of the Comprehensive Conservation and Management Plan.
  • The eelgrass target is a component of the Coastal Habitat extent target.
  • USFWS eelgrass aerial surveys are only conducted in the eastern basin of Long Island Sound.
  • The increase in acreage in 2006 may reflect better imagery used from the first aerial flight and/or better environmental conditions during the aerial flight.
  • *Two large beds totaling 122.1 acres on the south side of Fishers Island could  be seen on the 2009 imagery from the survey while they were not visible on  2006 imagery due to environmental conditions. Field inspections in 2006 had located robust beds in this area and recorded their occurrence as points since the beds could not be accurately delineated on the imagery. Consequently, the 2009 Eelgrass Survey does not treat this acreage as a gain because the Fishers Island beds were noted in 2006, but  their boundaries could not be established.
  • **In earlier surveys a 2.1-acre low density eelgrass was mapped at the mouth of the Connecticut River because it was identified by field personnel. In the 2012 imagery, this bed was not detected so it is not included in this survey.
  • The US Fish and Wildlife Service’s National Wetlands Inventory Program (NWI) has conducted eelgrass inventories for the eastern end of Long Island Sound since 2002. To date, four surveys have been conducted. These inventories were started because the State of Connecticut’s Office of Long Island Sound Programs was interested in learning the status of eelgrass beds in 2001 and wanted the beds monitored periodically.
  • Detailed information on the extent of eelgrass in individual Long Island Sound embayments is available at the National Wetland Inventory website. A free online digital map server, the NWI+ data mapper allows open access to wetland GIS layers for the general public to view and edit.  It can be downloaded at . A link to a brief tutorial is available on this page in the “Learn More” section .


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Related Ecosystem Targets

  • Coastal Habitat Extent
  • Water Clarity

Supporting Indicators

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