Water Column Effects on In Situ Spectral Signatures of Coral Species from Gujarat Coast, India

Scleractinian corals represent the main functional group in a coral reef ecosystem. So far, very few studies have ever reported how an in situ coral spectra changes with increasing water column purely in a natural environment. This paper reports the results of a unique field experiment wherein water column effects were observed over time on in situ hyperspectral signatures (over a continuous spectral range 400–1350 nm) of three live coral species from Gujarat coast of India. In situ hyperspectral measurements were taken with Analytical Spectral Devices (ASD) FieldSpec3 spectroradiometer having full spectral range of 350–2500 nm and spectral resolution of 3 nm (at 700 nm) and 10 nm (at 1400, 2100 nm). Three coral species, Favia favus , Goniopora planulata and Turbinaria peltata , were selected as case representatives for this study. In exposed condition, all three corals exhibit brown mode of coral reflectance with characteristic triple peaks at 575, 600 and 650 nm. It is observed that water column attenuates the original signature of corals by enhancing the spectral magnitude in the visible region and in inverse fashion in the infrared region. The first derivative spectra clearly bring out the sensitivity of 840-nm channel towards water column. The water column height at which the triple peak pattern gets obscured varies for the three coral species. The spectral reflectance of coral as a bottom substrate continues to remain strong between 700–720 and 1050–1080 nm even in marginally submerged condition.