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The impacts of climate change and post bleaching effects on the octocoral communities of Gulf of Mannar, India

Abstract

The objective of the present study is to assess the status of the octocoral communities, and the extent of bleaching they suffered in 2016 (in line with the third Global Bleaching Event). Bleaching survey was carried out in the permanently fixed study sites in the 21 island of Gulf of Mannar. A focused study was carried out in Kariyachalli Island to monitor post-bleaching effects on octocorals. The overall octocoral cover in 2015 was 1.59±0.29%, and octocoral genera such as Sinularia, Sarcophyton, Lobophytum and Subergorgia were observed predominantly in GoM (Gulf of Mannar). Temperature reached a maximum of 32.5°C (March) during 2016 bleaching. The extent of bleaching in 2016 was 1.05±0.65% and the overall octocoral cover was reduced to 1.16±0.22%. Multiple paired t-test results indicate a significant variation in the octocoral covers between 2015 and 2016 (t = 3.173, p < 0.01). Sinularia, Xenia, and Subergorgia were the most affected genera during this bleaching episode. The percentage bleaching in octocorals was the highest in Vembar group of islands (1.9±0.62%) and the continuous monitoring studies reveal the increase in the octocorals diversity from 1.16±0.22% to 1.34±0.21% in 2018 indicating the recovery pattern of octocorals in GoM. Post-bleaching surveys carried out in Kariyachalli Island revealed the occurrence of tissue degradation and algal overgrowth following the bleaching event. However, this study concludes that octocorals in GoM could adapt and flourish in the context of changing climatic conditions. However, more studies on octocoral ecology and biology are warranted.

Research highlights

  • Percentage cover of the octocorals in Gulf of Mannar was assessed with a total of 16 octocoral genera was recorded during the study.

  • The octocoral cover decreased from 1.59±0.29% (2015) to 1.16±0.22% (2016) and then again increased to 1.34% (2018); with the extent of bleaching of 1.05±0.65% (2016).

  • Sinularia, Xenia and Subergorgia were the most affected genera during this bleaching episode of octocorals.

  • Unusual tulf algal overgrowth with tissue degradation was witnessed in the octocoral genera Sinularia sp.

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Acknowledgements

We would like to thank the Ministry of Environment, Forest and Climate Change, Government of India for the funding support; Tamil Nadu Forest Department for research permissions (Ref. No. WL (A)/ 11868/2017, Permit No. 24/2017); and reef research team of SDMRI for the support during the entire field work.

Funding

Dr Patterson provided guidance, logistics, funding and support to carry out research work, and reviewed the manuscript. Dr Dinesh Kumar did field visits for gathering data, underwater visual senses and in-situ photographs. Ms Mahalakshmi drafted the original manuscript, statistics and the figures in the manuscript.

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Correspondence to Mahalakshmi Boopathi.

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This article is part of the Topical Collection: Advances in Coastal Research.

Communicated by Shambanagouda R Marigoudar

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Boopathi, M., Kumar, P.D. & Edward, J.K.P. The impacts of climate change and post bleaching effects on the octocoral communities of Gulf of Mannar, India. J Earth Syst Sci 130, 208 (2021). https://doi.org/10.1007/s12040-021-01701-3

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Keywords

  • Bleaching
  • hard corals
  • octocorals
  • recovery