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Eelgrass Mapping

Harpswell Heritage Land Trust
November 1, 2021

By Rep. Jay McCreight

On July 8, 2021, Governor Mills signed into law a bill that establishes regular mapping of eelgrass beds and salt marsh vegetation in the state. In five-year cycles, each segment of the coast from Southern Maine to Downeast Maine will be mapped, providing up-to-date information about the presence and health of these important natural resources.


Mapping will be managed by the Maine Department of Environmental Protection (DEP) in consultation with the Maine Department of Marine Resources and will begin in the summer of 2023 along the Midcoast region. It will be based on aerial imagery as contracted by Maine DEP. The products from the mapping program will be the low tide orthoimagery and GIS layers showing seagrass and salt marsh extent and will be analyzed by Maine DEP staff. Results will be available publicly through the Maine Geolibrary website. In addition, the law requires a biennial report to the Legislature, to be posted publicly through the Maine DEP website.

Eelgrass had been mapped in the 1990s and early 2000s, but the program ended when a staff member doing the work retired and priorities shifted. Since then only intermittent and limited mapping was possible. In light of the current climate crisis, it has become increasingly clear that establishing a regular, robust program of mapping along the entire coastline is incredibly important to the health of our entire coastal ecosystem.

Both eelgrass and salt marsh vegetation provide critical benefits for the health and sustainability of our coastal environment. They are “carbon sinks” — powerhouses of carbon absorption and storage that hold carbon that would otherwise be released into the atmosphere in the form of carbon dioxide — helping to mitigate greenhouse gas emissions. They also provide critical habitat for young aquatic creatures, foraging areas and shelter for young fish and invertebrates, food for migratory waterfowl and spawning areas for many aquatic species. Importantly, eelgrass beds and salt marshes also provide buffers that help mitigate shoreline erosion and protect water quality by filtering polluted runoff and removing excess nutrients.

Specific to Harpswell’s eelgrass resource, our extensive shallow shoreline offers an hospitable environment for eelgrass and it has proliferated. However, as was obvious to Harpswell residents in 2011-2012, the infestation of green crabs removed a significant amount in eelgrass. Maine DEP reports that the eel grass is coming back and that trend is expected to continue, though clearly the resource can be suddenly and severely impacted. Regular, reliable mapping of the entire coastline will give us the information we need to identify where these important resources are and allow us to preserve and, where possible, restore them. In addition, mapping will be used, among other things, for Natural Resources Protection Act permitting, oil spill response actions and for review of aquaculture lease applications.

This new law came to be because of the collaborative work of many in our coastal communities who care deeply about our state, our environment, and our ability to preserve and restore critical resources. The new law can be found by clicking here.