Discrimination of common New Zealand native seaweeds from the invasive Undaria pinnatifida using hyperspectral data

Undaria pinnatifida (Harvey) Suringar, native to north-western Asia, is a prolific invasive seaweed species that has established across much of New Zealand, competing and co-existing with native seaweed species. Remote sensing could be used to map both invasive and native seaweeds in New Zealand. The aim of this study is to evaluate the hyperspectral differences (and the wavelengths at which they differ) between New Zealand seaweed species at broad taxonomic levels and also between Undaria pinnatifida and other common New Zealand seaweeds. ASD Handheld2 VNIR spectroradiometer with a spectral range of 325 to 1075 nm was used to collect hyperspectral data of the common New Zealand native and invasive seaweed species. Two supervised classification methods such as partial least-square discriminant analysis (PLS-DA) for wavelength selection/classification and random forest for validating the results from PLS-DA were implemented. The seaweed species were separable at broad taxonomic level with accuracies greater than 85% for all three taxonomic groups using PLS-DA. The influential wavelengths in discrimination were 572, 633 to 635, 640, 657 to 661, 687, 704 to 714, 741, 742, 749, and 750 nm. Some of the influential wavelengths were consistent with pigment absorption peaks unique to red and brown seaweeds. Undaria pinnatifida showed differences from native brown seaweed species in the visible (574 nm) and near-infrared (716 to 721, 750 nm) region of the electromagnetic spectrum. It was classified with an accuracy of 97.7% and 90.7% using random forest and PLS-DA, respectively.