Name: Seagrass 2023

Display Field: Polygon_ID

Type: Feature Layer

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Description: <DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>This dataset contains the seagrass beds delineated in 2023 in the Midcoast Region, from Small Point in Phippsburg to Marshall Point in Port Clyde. </SPAN></P><P><SPAN>Polygons were screen digitized from aerial imagery flown at low tide on July 7, August 2, August 3, and August 6, 2023. Imagery was captured using a Vexcel Eagle 80-mm Mark 3 aerial camera mounted on a fixed wing aircraft and flown at an elevation of approximately 9,500 feet. Polygons were refined based on field verification efforts that took place between August 14 and October 11, 2023. Field verification was carried out by boat using a Maine DEP vessel (20-foot Maritime Skiff with a 115 horse outboard motor, 12' Tracker with 5 horse outboard motor, or canoe), SeaViewer Admiral Pro High-Definition (HD) georeferenced underwater videography package with SeaViewer 6000 Sea Drop underwater video camera, and Juniper Systems Geode GNS3S GNSS GPS system capable of submeter accuracy that paired wirelessly to Samsung Tab Active3 ruggedized field tablets.</SPAN></P><P><SPAN>Each contiguous seagrass bed is named by sequential number moving from west to east along the coast, which is provided in the ‘Bed_Name’ column. These beds are further divided into polygons by percent cover. Polygons are labeled with a unique identifier consisting of sequential numbers in the ‘Polygon_ID’ column. A singular bed can consist of several polygons IDs. Percent cover categories and percentages are based on those established by Orth et al. (1991), where 1=0-10% cover (very sparse), 2=10-40% cover (sparse), 3=40-70% cover (moderate), 4=70-100% cover (dense).</SPAN></P><P><SPAN>This seagrass polygon shapefile also contains fields for whether the bed was field verified in 2023 (Y=yes or N=no) and whether there is corresponding underwater video footage (Y=yes, N=no). Field verified beds were verified only in part, meaning one or more transects were placed along the perimeter of the bed to confirm seagrass presence and aerial signatures; bed boundaries were not verified in their entirety. Field verification refers to whether the bed (Bed_Name field) was visited, it does not account for individual parts of the bed (Polygon_ID field) with differing cover classes, though often verification occurred in more than one cover class per bed. Underwater video is present for most of the field verified beds but is lacking in some areas due to technical errors or logistical limitations on deploying video equipment. The video column corresponds to the named underwater video file, which corresponds to transect name. Species and comment fields are also incorporated in this dataset. Species are only noted if directly observed by underwater video or by visual observations in shallow water. Widgeon grass was observed only in a tributary to the Great Salt Bay, upstream of a culvert that likely restricts tidal flow. </SPAN></P></DIV></DIV></DIV>

Service Item Id: af4c834d3fc84352bb159611c353d15b

Copyright Text: Seagrasss mapping was produced by the State of Maine Department of Environmental Protection. Orthophotos for this effort were acquired by James W. Sewall and Bluesky Geospatial was subcontracted for aerial imagery acquisition and orthophotography development. The Maine Department of Environmental Protection Marine Vegetation Mapping Program completed the seagrass delineation.

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Spatial Reference: 26919  (26919)

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Fields:

• OBJECTID ( type: esriFieldTypeOID, alias: OBJECTID )
• Polygon_ID ( type: esriFieldTypeInteger, alias: Polygon_ID )
• Bed_Name ( type: esriFieldTypeInteger, alias: Bed_Name )
• Acres ( type: esriFieldTypeDouble, alias: Acres )
• Hectares ( type: esriFieldTypeDouble, alias: Hectares )
• Orth_Cover ( type: esriFieldTypeInteger, alias: Orth_Cover )
• Orth_Pct ( type: esriFieldTypeString, alias: Orth_Pct, length: 10 )
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• Video_YN ( type: esriFieldTypeString, alias: Video_YN, length: 1 )
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