Nationwide Seagrass Mapping Using Analysis-Ready PlanetScope Data to Support the Nationally Determined Contributions of Seychelles

Abstract

Seagrass meadows provide many valuable ecosystem services including blue carbon sequestration and habitat and nursery ground provisioning for commercial fish. Unfortunately, the conservation and research of these highly productive habitats are hampered by the inadequacy of their distribution and change in many regions.

Owing to seagrass living at the bottom of the water column, the dominant spaceborne remote sensing approach is optical. Furthermore, with the addition of the Planet & Norway’s International Climate and Forests Initiative (NICFI) onto Google Earth Engine (GEE), anyone can have free access to the 4.77 m high spatial resolution PlanetScope image composites between 2015 to present. Although terrestrially-focused, the presence of shallow waters within the buffered coastline in these composites allows the exploitation of NICFI for coastal remote sensing as well. Consequently, a potentially high-resolution, large-scale seagrass map could be produced with savings in time and cost.

In this study, we implement our multitemporal composition approach on GEE onto the PlanetScope composite archive in order to map the seagrass meadows of Seychelles on a national level. Beyond spectral bands, we also explore the use of object-based and texture methods on the classification results. Such methods have been reported to work well when applied on images with high spatial resolution and this study evaluates if this holds for the Seychellois seagrass maps.

The results will contribute to the development of a national seagrass mapping and monitoring blueprint, which is important for the assessment of national seagrass blue carbon stocks for the Nationally Determined Contributions for Seychelles as well as beyond.