Spectral Signatures of Macroalgae on Hawaiian reefs.

In Hawaiʻi, native macroalgae or “limu” are of ecological, cultural, and economic value. Invasive algae threaten native algae and coral that serve a key role in the reef ecosystem. Spectroscopy can be a valuable tool for species discrimination, while simultaneously providing insight into chemical processes occurring within photosynthetic organisms. The spectral identity and separability of Hawaiian macroalgal taxonomic groups and invasive and native macroalgae are poorly known and thus were the focus of this study. A macroalgal spectroscopic library of 30 species and species complexes found in Hawaiʻi was created. Spectral reflectance signatures were aligned with known absorption bands of division-specific photosynthetic pigments. Discriminant analysis was used to explore if taxonomic groups of algae and native versus invasive algae were separable. Discriminant analyses resulted in high overall classification accuracies. Algae were correctly classified based on taxonomic divisions 96.5% of the time and by species 83.2% of the time. Invasive versus native algae was correctly classified at a rate of 93% and higher. Analyses suggest there is spectral separability of algal taxonomic divisions and native-invasive status, which could have significant implications for coastal management. This study lays the groundwork for testing spectral mapping of native and invasive algal species using current airborne and forthcoming spaceborne imaging spectroscopy.