**6. Conclusion**

*Invertebrates - Ecophysiology and Management*

first derivative spectra are considered as reliable means for spectral discrimination as they are less function of noise as compared to the second derivative spectra [5, 9, 19]. The first derivatives of sampled live and bleached coral spectra (**Figure 5**) reaffirm the magnitude difference in reflectance values in the UV-visible region (i.e. 350–550 nm). At 557 nm and at the narrow window of 593–605 nm, the first derivatives of the live and apparently healthy corals record a positive slope, while the bleached corals record negative slopes. This trend is reversed at 625 and 645 nm when the first derivatives of bleached corals record a positive slope and that of the live ones record negative slopes. The window of 593–605 nm corresponds with the observation as reported earlier [11], and it is recommended to use 596 nm (i.e. the midpoint of this window) as a slope gradient discriminator to distinguish live, recently dead and bleached corals with high accuracy. The second derivatives (**Figure 6**) of the sampled live and bleached coral spectra identify two prominent zones of slope differences, i.e. 591–599 and 687–703 nm. In both these windows, the live corals record positive

*Second derivatives of sampled live and bleached corals (red dashed circles indicate the zones of slope differences* 

*First derivatives of sampled live and bleached corals (red dashed circles indicate the zones of slope differences in* 

second derivative values, while the bleached ones have negative values.

**126**

**Figure 5.**

**Figure 6.**

*in the derivative spectra) [5].*

*the derivative spectra) [5].*

As observed in this study, live and bleached corals get distinguished in the visible region over 500–600 nm. The first derivatives discriminate live and bleached corals at 557, 625 and 645 nm channels and also in the spectral window of 593–605 nm. The second derivatives separate live and bleached corals in two narrow spectral windows: 591–599 and 687–703 nm.

Wavelength-specific spectral discrimination of live and bleached coral spectra using derivatives, however, needs more number of in situ data samples collected from different coral species. The onset of mass coral bleaching events can provide such ideal real-time field conditions facilitating collection of this kind of species-specific in situ reflectance data of both live and bleached corals. Field spectroscopy is a potential non-invasive tool to provide first-hand information on the health or ecological status of the corals with reference to pigment level changes at organism or colony level.
