Seagrass beds are critical wetlands components of shallow coastal ecosystems throughout the state. Seagrass beds provide food and cover for a great variety of commercially and recreationally important fauna and their prey. The leaf canopy of the seagrass bed calms the water, filters suspended matter and together with extensive roots and rhizomes, stabilizes sediment.
Eelgrass and other seagrasses are often referred to as "Submerged Aquatic Vegetation" or SAV. This distinguishes them from algae, which are not classified as "plants" by biologists (rather they are often placed in the kingdom protista), and distinguishes them from the "emergent" saltwater plants found in salt marshes. In addition to the term SAV, some coastal managers use the term SRV or submerged rooted vegetation. This term probably arose to avoid confusion because non-scientists considered both seagrasses and algae as "plants" or "vegetation," and did not realize the term SAV excluded algae. (refer to http://www.buzzardsbay.org/eelgrass.htm)
The DEP Eelgrass layer, produced from data collected in 2001, is the second statewide mapping of the eelgrass resources along the coast. The data were compiled from similar methodologies as the earlier 1995 dataset. A similar third iteration of this statewide mapping is planned for the 2006-07 seasons.
Eelgrass, Zostera marina, is the most common seagrass present on the Massachusetts coastline. The other species found in embayments of the Massachusetts coast is Ruppia maritima, widgeon grass, is present in areas of less salinity along the Cape Cod and Buzzards Bay coast.
The layer is named EELGRASS_POLY. With the February 2006 update, which added the 2001 data, the EGRASVPT_PT layer of field verified points was discontinued.
The purpose of mapping the distribution of eelsgrass (Submerged Aquatic Vegetation - SAV) is to determine areas where the Zostera marina resource was decreasing in area and cover. The methods used for the 2001 were similar to those used in the earlier 1995. One exception to this specification was the change in the delineatation of apparent areas of no Zostera within polygons of the resource (i.e. holes). This change in mapping convention was derived from a better understanding of the scientific literature of the dynamics of Zostera beds which describes subtle "infra" movement within beds in response to day-to-day wave action, currents and sand migration, and storm events.