Wilson, K.L., Wong, M.C., and Devred, E. 2024. Mapping eelgrass habitat in southern Nova
Scotia with Worldview-2/3 satellite imagery. Canadian Technical Report of Fisheries and Aquatic Sciences 3629: ix + 42 p.(Mapping eelgrass habitat in southern Nova Scotia with Worldview-2/3 satellite imagery / by Kristen L. Wilson, Melisa C. Wong, and Emmanuel Devred.: Fs97-6/3629E-PDF - Government of Canada Publications - Canada.ca).
Abstract
Eelgrass (Zostera marina), the dominant species of seagrass in the Maritime provinces, provides many ecosystem functions and services. As such, maps that quantify its spatial distribution are a highly sought after data layer. Using eight Worldview-2/3 satellite images, we explored the ability to map eelgrass habitat across a gradient of environmental conditions along the South Shore of Nova Scotia. We found that Worldview-2/3 can routinely and accurately map submerged aquatic vegetation, as well as having some skill in differentiating eelgrass from other vegetation. This skill results from the habitat structure of eelgrass in this region which was often shallow (<3 m) and found in large monospecific beds. As expected, this skill decreased as bed size decreased and the predominance of other submerged vegetation increased. The maximum depth at which bottom habitat was detectable ranged from 1 to 12 m depending on water transparency. We demonstrated that Worldview-2/3 can detect changes in the surface area of eelgrass habitat between spring and summer, albeit issues in the satellite image quality related to sunglint, coloured dissolved organic matter concentration and sediment load may limit this ability. In total, 130 km2 of habitat type were mapped across the eight images, covering 92 km2 along the South shore after duplicated mapping events were removed (i.e., change detection).
Figure 3 Example of seasonal mismatch between the field survey data and image classification. Field survey Station 16 (purple cross; a) and Station 17 (red cross; b) median spectral signature (black line) and minimum to maximum range (green polygon). May 19, 2020 Worldview-2 imagery RGB (c) showing field survey points versus an August 2020 Sentinel-2 image (d). Vegetated habitat probability classification on the May Worldview-2 image (e) and the modal vegetated habitat map indicating areas that are likely seaweed dominated versus eelgrass dominant habitat (f). Light grey is land, dark grey is unclassified deep water.
