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 sc ientific basis of these reports is questionable. There exists no objec tive measure of coral health, so that individual perceptions of the pa leness of an individual comb head or an entire coral reef, a-e the fou ndation of coral bleaching reports. It is uncle-stood that coral blenc hing results from an expulsion or reduction of the algae housed in the individual polyp, which causes the cor-nl to lose its color. Satellit e or airborne remote sensing may be a feasible means of mapping and mo nitoring cor-al reefs over large geographic areas if a quantitative ?m eans of remotely determining coral health can be developed. In an effo rt to remotely detect co ml stress, in.situ spectral rflectance of hea lthy and bleached Fijian scleractinian combs was measured with a handh eld spectroradiometer. Principal components and cluster analysis revea led 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 f or remote identification of substrate type. These results are encourag ing with respect to using an airborne spectroradiometer to identify ar eas of bleached corals thus enabling accurate monitoring. over time. ( C) Elsevier Science Inc., 1998.