Mapping broad-scale habitat types at the Mercury Islands, northeastern Aotearoa New Zealand, using supervised classification of satellite imagery

Mapping the broad-scale distribution and extent of marine habitats is critical to developing an ecosystem-based approach to managing the marine environment as well as monitoring large-scale changes in these habitats over time. Utilisation of existing satellite and aerial imagery of coastal regions can provide a cost-effective approach to mapping broad-scale habitat types in the shallow subtidal marine environment.

In this study, we use multi-spectral satellite imagery of the Mercury Islands, northeastern Aotearoa New Zealand, to map broad-scale marine habitats in shallow water (<15-20 m depth) around the island group. Supervised classification techniques were used to classify and map broad-scale reef and soft sediment habitat types. Georeferenced ground truth photos of shallow habitats were taken using drop camera and diver-based surveys across a range of sites in March 2022 and used to carry out accuracy assessment of resulting maps. Due to limited availability of concurrent satellite imagery with good weather and sea conditions across the entire island group, shallow water habitats around Ahuahu-Great Mercury Island and the eastern Mercury islands were mapped separately using satellite imagery from July 2020 and March 2016 respectively.