1. Key Laboratory of Tropical Marine Bio-Resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
2. National Experiment Station of Tropical Marine Biology, Sanya 572000, China
3. Shandong Ji’ning No.1 People’s Hospital, Ji’ning 272111, China
4. Sanya Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China
Abstract：In order to further understand the spectral characteristics of different shapes and different colors of scleractinian coral, reflectance spectra of two common scleractinian coral species (brown schistose Turbinaria peltata and blue gray massive Platygyra daeda) were measured using a fiber spectrometer in the sea area of Lu Huitou Sanya Bay in the north-western South China Sea (SCS). On the morning of July 22, 2015, 7 samples for each species were collected. The size of the samples was ~6 cm, and was fostered to laboratory reef aquariums, in which water temperature was controlled ~26 ℃. The reflectance spectra were measured after the samples were fostered for more than 4 hours in the reef aquarium, and weather condition was sunny day without clouds. Using a spectrometer (USB2000+), band 200～850 nm, resolution 1.34 nm, step length 0.6 nm, and field angle 25 degrees, the sample was placed on the cylinder platform, and ~26 ℃ seawater was continuously injected to ensure the water temperature was constant. The extra seawater automatically spilt from the upper edge of the aquarium to exclude the “converging phenomenon” of the refraction of light into the water body. The black nylon cloth was adhered to the inter side wall of the aquarium to avoid the reflection effect. The distance between the probe and the sample was 5 cm, and the reflectance was the average of repeated 10 times measurements. The light source was the sun light, and the calibration of the spectrometer was carried out every time before the measurement, and reflectance spectrum in the visible light band was used to analyze the character of the reflectance of the samples. Then for spectral reflectance analysis, derivative spectroscopy was used to study the difference of the reflectance spectrum of them. The results showed that the reflectance of two kinds of coral is obviously different from each other in the visible wavelength range. The reflectance of Platygyra daeda was significantly higher than that of Turbinaria peltata with significant differences, and a similar high reflectance appeared only near 700 nm. The reflectance of Turbinaria peltata was between 4% and 15% with significant peak and trough. In 400～450 nm area reflectance of Turbinaria peltata showed a relatively lower value of about 4%～5%; after 480 nm it soared to around 10%, and obvious peaks appeared at 502, 578, 604 and 652 nm, and the main peaks at 604 nm, and 578 and 652 nm were the two shoulders; obviously the trough appeared at 670 nm, then surged to 36% at 700 nm. The reflectance of Platygyra daeda was between 6% and 16% with no obvious peak and trough. The reflectance values were relatively lower around 6% near 400～420 nm, increased sharply to about 15% with large characteristic peaks near 486 nm, at 486, 577, 607 and 650 nm there were four distinct peaks; with 607 nm as the main peak, 577 and 650 nm were the two shoulders; a significant trough appeared near 415 nm, and a less obvious trough appeared at 667 nm, then the reflectance increased significantly to about 37% at 700 nm. Derivative analysis results showed that the distinguishable bands of Turbinaria peltata and Platygyra daeda were as follows: first order derivatives are mainly in 483.7～492.6，496.2～500 and 533.5～540.5 nm bands. The second order derivatives are mainly in 414～422.7，499.4～504，520.2～523.3，534.2～536.6，557.5～561 and 671.8～675 nm bands. The fourth order derivatives are mainly in 414～417.6，427.4～430.3，433.4～436.5，452.3～455.5 and 657.1～659.1 nm.
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