BENTHIC GEOLOGIC HABITAT CHARACTERIZATION AND MAPPING OF FOUR SUBSECTIONS OF ACADIA NATIONAL PARK

Four areas around Acadia National Park including portions of Compass Harbor, Frazer Creek, Ship Harbor and Thompson Island were mapped using a combination of interferometric side-scan sonar, underwater video imagery and benthic grab samples in September 2021. This represents baseline mapping of these areas and applied the Coastal Marine Ecosystem Classification System (CMECS) covering a variety of representative habitats ranging from rocky intertidal areas (both bedrock and boulders) to intertidal and shallow subtidal mud flats. The sites vary in water depth, relative wave energy and bedrock geology. Previous mapping in the region focused on the broader inner continental shelf and while this represents seminal work on the Gulf of Maine, did not feature full-coverage side-scan sonar, particularly in shallow waters. The total side-scan sonar coverage over 4 field days encompassed 2.1 km² (512 acres). The intertidal focus of this project limited mapping to ~6hr windows around high tide and weather further limited surveys at Compass Harbor. Interferometric bathymetry covered roughly 50% of the side-scan sonar, limited to a maximum swath width of 6 times the water depth. Sediment samples (n = 40) and underwater videos (n = 59) supplied ground-truth for sonar interpretation. Side-scan sonar facies, unique areas of the seafloor based on the texture and intensity of the returning sonar signal were heads-up digitized and classified using the CMECS Substrate Component. Units ranged from muddy/silty to boulder and bedrock outcrop. The geomorphology of the four areas was described using the CMECS Geoform Component with a combination of side-scan sonar, interferometric bathymetry and digital orthophotographs. The resulting Substrate and Geoform layers were intersected in ESRI ArcMap, producing geologic habitats of the four study areas. On-going work focuses on the biota collected from the surface sediment grab samples and underwater video imagery, although notable biologic features identified thus far include a 0.4-acre Eelgrass (Zostera marina) bed in Compass Harbor and abundant Green Crabs (Carcinus maenas), an invasive species identified in underwater video imagery at Thompson Island. Dredge trails from the harvesting of mussels were mapped at Thompson Island showing a level of human disturbance of this site.