Abstract
Spectral characteristics of nine coral species (Acropora Nobilis, Acropora Hyacinthus, Acropora Varibalis, Favia Speciosa, Favia Stelligera, Porites Lobdata, Porites sp., Pocillopora Domicornis and branched dead corals), two seagrass species (Zosteraceae and Posidoniaceae), two sand benthic communities (sand mixed with coral rubble and carbonate sand), reef vegetation and sea moss were recorded using RAMSES-TriOS Hyperspectral radiometer from Mandapam group of islands, Gulf of Mannar, India. Based on the reflectance features, coral reef benthic compositions were categorized as brown mode and blue mode. Brown mode of corals was identified by a triple peaked pattern exhibiting local maxima or shoulders near 575, 600 and 650 nm. The blue modes of corals were identified by a plateau-like shape between 600 and 650 nm. The non-coral benthic compositions such as seagrass and sea moss can be identified by a peak between 550 and 560 nm. Results exhibited that, most of the coral reef benthic compositions falling under either blue mode or brown mode of corals and the patterns of spectral signatures exhibited in this region are matching with existing global signatures.
Research Highlights
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1.
This study attempts to analyse the spectral characteristics of nine different coral reef species species (Acropora Nobilis, Acropora Hyacinthus, Acropora Varibalis, Favia Speciosa, Favia Stelligera, Porites Lobdata, Porites sp., Pocillopora Domicornis and Branched dead corals) along with several of its associated benthic compositions two seagrass species (Zosteraceae and Posidoniaceae), two sand benthic communities (sand mixed with coral rubble and Carbonate sand), reef vegetation and sea moss recorded from various islands of Gulf of Mannar, India
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Results revealed that several coral species either fall under the broad category of Brown mode or Blue mode. Brown mode of corals was identified by a triple peaked pattern exhibiting local maxima or shoulders near 575, 600 and 650 nm. The blue modes of corals were identified by a plateau-like shape between 600 and 650 nm. The non-coral species such as seagrass and sea moss can be identified by a peak between 550 and 560 nm.
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It can also be noted that, irrespective of water column conditions; (i) all the coral reef benthic compositions tend to have its reflectance minimum around 674 nm (This phenomenon is due to the strong absorption of chlorophyll in that portion of EMR). (ii) Influence of water column can be seen in the rise of magnitude in the longer wavelengths of EMR for the measurements recorded based on exposed condition.
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Results exhibited that, most of the coral reef benthic compositions falling under either Blue mode or Brown mode of corals and the patterns of spectral signatures exhibited in this region are matching with existing global signatures.
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Acknowledgements
This work is supported by the Network Project on Imaging Spectroscopy and Applications (NISA), Interdisciplinary Cyber Physical Systems Division, Department of Science and Technology, Ministry of Science and Technology, Government of India, under grant BDID/01/23/2014-HSRS/17 (WAT-V). The authors are grateful to Prof Palanisamy Shanmugam, Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai and his team for helping in collecting in-situ measurements.
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Kandasami Nimalan performed the in-situ radiometric measurements, analyzed the data, designed the figures and wrote the manuscript in consultation with Muniappan Thanikachalam, and Tune Usha. Muniappan Thanikachalam has received the grant, involved in radiometric measurements and guided in manuscript preparation. Tune Usha provided critical feedback and helped shape the research and all authors discussed the results and commented on the manuscript.
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Nimalan, K., Thanikachalam, M. & Usha, T. Spectral characteristics of coral reef benthic compositions in Gulf of Mannar. J Earth Syst Sci 130, 58 (2021). https://doi.org/10.1007/s12040-021-01571-9
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DOI: https://doi.org/10.1007/s12040-021-01571-9