Regional Studies in Marine Science 39 (2020) 101429 Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Current biodiversity of Mandapam group of Islands in Gulf of Mannar Marine Biosphere Reserve, Southeast coast of Tamil Nadu, India CH. Ramesh a,∗ , S. Koushik a , T. Shunmugaraj a , M.V. Ramana Murthy b a National Centre for Coastal Research (NCCR), Ministry of Earth Sciences (MoES) NCCR Field Office, Mandapam 623519, Tamil Nadu, India b National Centre for Coastal Research, Pallikaranai, Chennai 600100, Tamil Nadu, India article info Article history: Received 22 November 2019 Received in revised form 12 August 2020 Accepted 23 August 2020 Available online 27 August 2020 Keywords: Coral reefs Macroalgae Invertebrates Reef fish Gulf of Mannar abstract The global climate change is known to involve in the decline of biodiversity from different ecosystems, including coral reefs worldwide. The spatial distribution of reef associated flora and fauna in the Gulf of Mannar (GoM) Marine Biosphere Reserve (GOMMBR) are declined due to damage of coral reefs by three major global problems observed in coral reefs, pertaining to frequent bleaching events, sedimentation and overwhelming algal communities. The occurrence of rich biodiversity in reef areas indicates the healthy condition of an iconic reef ecosystem. In this study, to assess the health status of coral reefs in Mandapam group of Islands under GoM, the diversity and distribution patterns of species composition assembled in reefs at seven Islands were analyzed. In 2019, summer temperature range was exceeded between 32 to 36 ◦ C than usual range 28 to 30 ◦ C, which resulted again massive coral bleaching in GoM. Statistical analysis revealed the high diversity of macroalgae in all the reef sites at Mandapam group Islands. Considerably, dead reefs in Mandapam group Islands represent 90% of algal communities and very less to scarce faunal diversity. While, faunal diversity was well diversified in the live coral cover areas and reefs with less macroalgal assemblage. This assessment provides current reef biodiversity data for gaining further insights into complex spatial distribution patterns of reef biota in GoM, and this will support the authorities to plan conservation efforts and to support livelihood of local fisher folk community. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Coral reefs are highly productive and biodiverse ecosystems on earth that provide an array of ecological services to nature and human (Moberg and Folke, 1999). Coral reefs provide seafood, seaweeds, medicinal sources, ornamental shells, and ornamental fish, act as spawning, nursery, breeding, feeding, and recreation grounds, supplies nutrients to pelagic food web, act as pollu- tion and climate change indicators, fixes atmospheric nitrogen, regulates CO 2 and Ca levels, and protect coastal environments by buffering of waves and currents (Moberg and Folke, 1999). Coral reef ecosystems require an optimal range of temperature between 21.7 to 29.6 ◦ C for the development, recruitment and resilience of coral reefs in tropical environments (Guan et al., 2015). In the current global warming scenario, the elevated tem- peratures around the globe are extirpating coral reef ecosystems worldwide (Burke et al., 2011; Camp et al., 2018). Damage of local and global reef ecosystems via frequent bleaching events, sedimentation, diseases, eutrophication, invasive algal species, ∗ Corresponding author. E-mail address: chrameshpu@gmail.com (CH. Ramesh). sponges, gastropods, worms, crown-of-thorns starfish, mining ac- tivities, fishing, recreation and other detrimental impacts (e.g. in- creasing atmospheric CO 2 levels, El Niño, cyclones etc.) are ap- pearing to cause severe negative impact on benthic and pelagic reef communities (Mohammed and Mohammed, 2005; Pratchett et al., 2011; Burke et al., 2011; Ponti et al., 2016; Renfro and Chadwick, 2017; Obura et al., 2017; Keith et al., 2018; Claar et al., 2018; Richards and Day, 2018; Ramesh et al., 2019). To understand the current status on reef diversity worldwide, assessment on reef communities is conducted timely in different reef ecosystems around the world, including Australia, Britany, Jamaica, Red Sea, Caribbean, and Florida, and emphasized the decline and spatial shift of reef communities including corals, algae, invertebrates and fish (Vertino et al., 2014; de Bakker et al., 2017). Coral-algal phase shift dynamics have been well studied to understand the negative impact of algae on the survival of live coral cover and coral recruitment (Burke et al., 2011), and reef fish assemblage (Ainsworth and Mumby, 2015). Coral-algal phase shift dynamics are evidently altering the reef fish commu- nities via reducing fishery production (Ainsworth and Mumby, 2015). Therefore many studies have raised the global alarm on reef conservation and reef restoration to maintain the healthy biodiversity. https://doi.org/10.1016/j.rsma.2020.101429 2352-4855/© 2020 Elsevier B.V. All rights reserved.