Using hyperspectral imagery to investigate large-scale seagrass cover and genus distribution in a temperate coast

Seagrasses are regarded as indicators and first line of impact for anthropogenic activities affecting the coasts. The underlying mechanisms driving seagrass cover however have been mostly studied on small scales, making it difficult to establish the connection to seagrass dynamics in an impacted seascape. In this study, hyperspectral airborne imagery, trained from field surveys, was used to investigate broadscale seagrass cover and genus distribution along the coast of Adelaide, South Australia. Overall mapping accuracy was high for both seagrass cover (98%, Kappa = 0.93), and genus level classification (85%, Kappa = 0.76). Spectral separability allowed confident genus mapping in waters up to 10 m depth, revealing a 3.5 ratio between the cover of the dominant Posidonia and Amphibolis. The work identified the absence of Amphibolis in areas historically affected by anthropogenic discharges, which occasionally contained Posidonia and might be recovering. The results suggest hyperspectral imagery as a useful tool to investigate the interplay between seagrass cover and genus distribution at large spatial scales.