Eelgrass Mapping Project

The current MassDEP Eelgrass layer is being updated. A paper has been published explaining the methodology of the updates.

Table of Contents

Eelgrass Monitoring Layers Updated on MassGIS

The MassGIS viewer allows the user to select and review the areal extents of eelgrass (Zostera marina) in a specific set of project areas during the different time periods MassDEP had conducted surveys using remote sensing (digital aerial imagery interpretation). For the most part, the data for the individual project areas is complete; however, some areas will be labeled as 'Incomplete' denoting that a portion of the area did not have suitable aerial imagery to effectively map the eelgrass resource.

Key Actions for Eelgrass Monitoring Layers Updated on MassGIS

Twelve Year Mapping & Change Analysis of Eelgrass (Zostera marina)

MassDEP commenced its Eelgrass Mapping and Monitoring Program in 1994 as an extension of its on-going Wetlands Mapping Program. Prior to this time little was known of the areal extent of the eelgrass resource statewide and isolated reports had suggested that the resource was in significant decline.

The ecological and economic importance of the seagrass, Zostera marina (eelgrass) in coastal waters of the western Atlantic is widely known. As far back as the 16th and 17th centuries Z. marina was recognized for its value in sustaining waterfowl, providing habitat for fisheries, substrate for shellfish, and as a crucial component of sediment and shoreline stabilization. Humans harvested eelgrass for use as insulation, filler materials in bedding and as compost for agriculture. Concern for the loss of these valuable services was magnified in the 1930s when the "wasting disease" decimated a large fraction of the North Atlantic populations of Z. marina, including populations in Massachusetts. This large scale decline led to a coast-wide reconnaissance of eelgrass abundance and numerous local investigations that continued for nearly three decades and. However, it wasn't until the 1980s when the first attempts were made to quantitatively map seagrass distribution and abundance in selected portions of the Massachusetts coast on a large scale.

Costa (Costa 1988) identified 4,099 hectares (ha) of Z. marina along a portion of the Massachusetts coastline in the near shore waters of Buzzards Bay and predicted that eelgrass was returning to its former abundance prior to the wasting disease. Costa also identified embayments where Z. marina had not yet returned in water bodies corresponding with nitrogen loading, degraded water quality and eutrophication (Valiela and Costa 1988; Costa et al. 1992). In Waquoit Bay on the south shore of Cape Cod, seagrass declines were directly linked to eutrophication caused by nitrogen loading from septic tanks. Subsequent empirical and modeling studies in Massachusetts estuaries have linked land-derived nitrogen loading through groundwater and other sources directly to the growth of macroalgae and the decline of Z. marina. Eutrophication causes excessive organic enrichment in sediments, acute and chronic anoxia, and severe physiological stress on eelgrass plants that may already be experiencing light limitation (Holmer and Larsen 2002).Unlike situations where degraded optical water quality reduces light penetration and threatens plants mostly in the deeper water, the effects of multiple stressors associated with eutrophication cause more widespread losses of eelgrass which are not just confined to the deepest edges of the seagrass beds.

Results from the studies in Massachusetts and several related national and international research programs have converged to identify the detrimental effects of nutrient enrichment and eutrophication in coastal waters including large-scale declines of seagrass meadows. These studies suggested that seagrass can potentially serve as sentinels of coastal environmental change associated with natural and anthropogenic disturbances. With appropriate temporal and spatial scaling, monitoring environmental quality and mapping the changes in seagrass distribution and abundance can provide scientists and managers with a sensitive tool for detecting and diagnosing environmental conditions responsible for the loss or gain of seagrasses. Such a tool can a help to establish realistic goals in estuarine ecosystem restoration programs (Tomasko et al. 2001; Kemp et al. 2004; Steward and Green 2007; Waycott et al 2009; Orth et al. 2010). Based on this, the Massachusetts Department of Environmental Protection (MassDEP) initiated a statewide "eelgrass change analysis program" to determine if Z. marina declines reported in portions of Buzzards and Waquoit Bays were more widespread in Massachusetts.

Statewide Seagrass Mapping 1994-2012

The Massachusetts statewide seagrass mapping effort was conducted in four phases beginning in 1994 and ending in 2012.

  1. 1995 - Entire Massachusetts coastline.
  2. 2001 - Entire Massachusetts coastline, excepting Billingsgate Shoals and the Elizabeth Islands.
  3. 2006 - Selected Embayments on Cape Cod, Buzzards Bay and Martha's Vineyard.
  4. 2010 - Selected Embayments on Cape Cod and Buzzards Bay.
  5. 2012 - Massachusetts Bay  coastline, Ipswich Bay to Provincetown

For a comprehensive description of the MassDEP Eelgrass Mapping and Monitoring Program, please refer to the following paper: "Twelve Year Mapping & Change Analysis of Eelgrass (Zostera marina) Areal Abundance in Massachusetts (USA) Identifies Statewide Decline".

Additional Resources for Statewide Seagrass Mapping 1994-2012

Image credits:  Charles Costello, MassDEP

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