Spectral discrimination of healthy and non-healthy corals based on cluster analysis, principal components analysis, and derivative spectroscopy

Report of global mass coral bleaching are of major concern, bit the scientific basis of these reports is questionable. There exists no objective measure of coral health, so that individual perceptions of the paleness of an individual comb head or an entire coral reef, a-e the foundation of coral bleaching reports. It is uncle-stood that coral blenching results from an expulsion or reduction of the algae housed in the individual polyp, which causes the cor-nl to lose its color. Satellite or airborne remote sensing may be a feasible means of mapping and monitoring cor-al reefs over large geographic areas if a quantitative ?means of remotely determining coral health can be developed. In an effort to remotely detect co ml stress, in.situ spectral rflectance of healthy and bleached Fijian scleractinian combs was measured with a handheld spectroradiometer. Principal components and cluster analysis revealed that there is a spectral distinction between healthy and bleached cor-al based largely on magnitude of reflectance. Spectral derivative analysis was used to determine the specific wavelength regions ideal for remote identification of substrate type. These results are encouraging with respect to using an airborne spectroradiometer to identify areas of bleached corals thus enabling accurate monitoring. over time. (C) Elsevier Science Inc., 1998.