Photos of the Long Island Sound

Research & Monitoring

Status and Trends: LISS Environmental Indicators

Eelgrass Abundance

LISS Eelgrass Survey, USFWS

Eelgrass Abundance
Acres
2002 1,598.5
2006 1,904.7
2009* 1,980.0
2012** 2,061.1

WHAT IS EELGRASS?

Eelgrass, Zostera marina, is a rooted underwater grass that grows along the coast. Eelgrass meadow habitat provides food and nesting grounds for fish, and food for many migratory birds. Today eelgrass is only found in the eastern Sound, but it was once common throughout. Eelgrass was nearly wiped out, first by a fungal disease in the 1930s, and more recently by poor water quality attributed to the effects of nitrogen pollution from sewage discharges and stormwater runoff.

WHAT DOES THIS INDICATE?

Eelgrass beds 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 can stimulate the overgrowth of phytoplankton (algal) blooms that could block the energy from the sunlight that eelgrass needs to grow.

STATUS

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).

DATA NOTES

  • 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 mappedat 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 http://nwiplus.cmi.vt.edu/nwiplusmapper/ . A link to a brief tutorial is available on this page in the “Learn More” section
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