13 © 2019 Conscientia Beam. All Rights Reserved. PURPLE-BLUE PIGMENTATION PRODUCTION AS A SIGN OF IMMUNE RESPONSE BY BLEACHED CORALS TO AVOID STRESS CAUSED BY ELEVATED SEA SURFACE TEMPERATURE CH. Ramesh 1+ S. Koushik 2 T. Shunmugaraj 3 M.V. Ramana Murthy 4 1,2,3 National Centre for Coastal Research (NCCR), Ministry of Earth Sciences (MoES) NCCR Field Office, Tamil Nadu, India. 4 NCCR, Pallikaranai, Chennai, Tamil Nadu, India. (+ Corresponding author) ABSTRACT Article History Received: 16 August 2019 Revised: 19 September 2019 Accepted: 22 October 2019 Published: 26 November 2019 Keywords Acropora Porites Blue pigmentation Bleaching Temperature Gulf of Mannar. Coral reefs are extensively studied around the world with regard to their taxonomy, distribution, diversity, bleaching events, diseases, conservation, and restoration aspects. However, exhibition of blue pigmentation by corals under certain stressed condition such as high temperature and bleaching events has not been widely investigated. In the present study, during a massive bleaching event of coral reefs in 21 islands of Gulf of Mannar Marine Biosphere Reserve, corals such as Acropora sp. and Turbinaria sp. and some other encrusting corals have displayed purple blue pigmentation in response to high temperature and to avoid complete bleaching of their food supplying symbiotic zooxanthellae. This documentation from this environment is being reported for the first time and thus further immunological and genomic studies are required to study the variation in the zooxanthellae in bleached and non-bleached corals as well as blue pigment showing and non-pigmented corals. The compound responsible for blue pigmentation is needed to be analyzed further which could be employed for other industrial and biomedical applications. Contribution/Originality: This study documents the purple blue pigmentation displayed by corals such as Acropora sp. and Turbinaria sp. and some other encrusting corals in response to high temperature. This is a sign of adaptation of corals to avoid stress and survive from massive bleaching event occurred in Gulf of Mannar, India. 1. INTRODUCTION Coral reefs are biodiversity rich hotspots in the ocean. Since the early 1980s, coral bleaching had been a major concern for the coral health due to its negative impact on reefs globally. In recent times, the frequently occurring bleaching events caused by climate change are known to damage corals enormously. The increased sea surface temperature (SST) is one of the major factors which triggering coral bleaching, where the symbiotic zooxanthellae (Symbiodinaecea) living inside the tissues of corals are expelled out due to unfavorable and stressed environmental conditions. Massive coral bleaching events destroying many reef habitats around the world were reported during 1998, 2005 to 2010 and 2016 [1]. Coral reefs in Gulf of Mannar Marine Biosphere Reserve (GOMMBR), Southeast coast of Tamil Nadu, India, are facing potential threats from bleaching events, sedimentation, invasive algal blooms and boring organisms like sponges. Recently, despite no El Niño, massive coral bleaching event have also been recorded in Australia, French Polynesia and GOMMBR due to elevated SST in 2019. Corals display different colours such as pink and blue due to various stress factors including damage or breakage of coral fragments, fish International Journal of Hydrology Research 2019 Vol. 4, No. 1, pp. 13-15 ISSN: 2771-5590 DOI: 10.18488/journal.108.2019.41.13.15 © 2019 Conscientia Beam. All Rights Reserved.