Eelgrass density and coverage in restored and unrestored sites around Mount Desert Island, Maine

Dorn, Nathan; Disney, Jane

From the abstract: "Eelgrass (Zostera marina) is a foundational marine species in nearshore ecosystems that provides numerous ecosystem services. As part of ongoing efforts to monitor and map eelgrass populations around Mount Desert Island, Maine, eelgrass shoot density, shoot height, flower number, and bed area were determined at multiple long-term monitoring sites. Two sites are located within Acadia National Park, and two sites are found outside the park, including one site that was previously restored. Water quality data was also collected, but results are not yet available. The differences between unrestored (Ship Harbor, Wonderland, Hadley Point East) and the restored site (Hadley Point West), along with shoot density and eelgrass coverage changes between 2018 and 2022 were of special interest. We found that sites in Acadia National Park (Ship Harbor, Wonderland) had the highest densities of shoots within eelgrass patches. Study sites from 2022 had a higher average shoot height compared to the same sites in 2018, while Hadley Point West had the highest average shoot height of 2022 study sites. Although flower numbers varied, no significant difference was found between sites for flower density. Following mapping protocol used by the Community Environmental Health Lab in 2017 and 2018, ArcGIS Field Maps and Trimble Mobile Manager programs were utilized to determine the size of eelgrass patches at each site. Compared to 2018 survey sites, all sites experiencednet eelgrass growth, with Hadley Point West notably increasing from no detectable eelgrass in2018 to 3.55 acres in the survey area in 2022. These results suggest existing eelgrass populations around Mount Desert Island may have higher levels of coverage and average shoot heights compared to 2018. While these findings provide an updated view on eelgrass ecosystems around Mount Desert Island, it is important for efforts to continue. Monitoring and research on the health and density of eelgrass populations is vital for understanding how these populations shift over time, especially under projected scenarios of warming and acidification in the Gulf of Maine. Continued mapping is necessary for effective management and conservation of this ecologically and economically important species in Maine’s coastal ecosystems."