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DEPT. OF MARINE RESOURCES
How Maine Eelgrass Maps Were Made
Maine's eelgrass meadows form an important marine and estuarine coastal aquatic habitat for the state. Along with other plants, eelgrass forms the base of food production in the sea. Eelgrass provides shelter for juvenile fish, and invertebrates, is a site for primary settlement of the larvae of some bivalve mollusks, and in certain locations helps to stabilize unconsolidated sediments and shorelines.
As a continuing project, sections of the coast have been flown and photographed using Kodak 2448 and 2427 film at a scale of 1:12000. This photography was supplemented in the Penobscot Bay region by 1992 flights using Kodak 2445 film. The Penobscot Bay flights were contracted by the Maine Department of Transportation and interpreted by Dr. Fred Short of the University of New Hampshire. Areas in the present study were flown in the July to October period during 1993 to 1997 and again in the 2001 to 2010 time period. When possible, photography was at the time of extreme low tides, low wind velocity, good water clarity, and maximum biomass of eelgrass. These factors aid in the detection of the subtidal portion a bed.
In the period 1992-1997, eelgrass bed locations were compiled on stable-base acetate manuscripts containing the coastline and other basemap features from the 1:24000 scale USGS topographic maps. Polygons delineating stands of eelgrass were digitized and coded using a four category scale of percent cover. In the 2001 to 2010 time period polygons were screen digitized.
Verification has been carried out by boat, on foot, and by plane. Though dense patches of eelgrass approximately 6 meters in diameter and less can be identified under good conditions and in some cases were mapped, a conservative estimate of the minimum mapping unit is 150 square meters. This represents a stand of approximately 14 meters in diameter.
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