Differential Bleaching Patterns in Corals of Palk Bay and the Gulf of Mannar

Abstract

The status of reefs in Palk Bay and the Gulf of Mannar was studied during April-May 2016 following a bleach alert, as the sea surface temperature recorded a sudden increase from 30.5C to 34.0C in Gulf of Mannar. About 71.48%  8.9% of the corals in Palk Bay and 46.04%  3.78% in Thoothukkudi group of Islands in Gulf of Mannar were found bleached, showing a clearly decreasing trend from north to south, which could be attributed to the corresponding pattern in intensity of SST recorded in the study sites. Observations of bleaching patterns among different life-forms showed 68% of the bleached corals were massive forms. It was observed that 22 out of the 26 massive forms were bleached, while the Acropora corymbose (ACC), digitate (ACD) and encrusting coral (CE) forms were not bleached in any of the study sites in Palk Bay and Gulf of Mannar. The study suggests that the ACC, ACD and CE forms have adapted to thermal stress, subsequent to the earlier mass bleaching events. The study highlights the need for understanding the molecular mechanism of the association between corals and the symbiotic algae, for further understanding on coral bleaching in Indian waters.

Health monitoring status of corals in Gulf of Mannar and Palk Bay (India) with special reference to coral bleaching event

“…However, a similar result was found in the present study, where the Tuticorin group of Islands represents a high number of bleached corals than other areas of GoM, followed by PB (Figure 5). Earlier studies documented that branching corals were more tolerant to increased SST than massive corals, which is a sign of prolonging adaptive bleaching patterns found in GoM (Krishnan et al 2018;Ramesh et al 2020). In the current study, species-specific evaluation of bleaching revealed the same pattern of bleaching in which massive corals such as P. lutea, P. solida, D. favus, D. speciosa, F. halicora are bleached intensively, whereas, bleaching among branching corals limited mainly to A. muricata, A. hyacinthus, and M. digitata.…”

“…This study documented some important reef health details of the coral communities, the relative abundance of coral species, the bleaching status of corals, and threats to the reefs that exist in GoM and PB. Coral reefs are fragile and highly virulent to natural and anthropogenic disturbances, including climate change, sedimentation, destructive fishing, shoreline operations, and tangling ghost nets (Krishnan et al 2018). Therefore, community structure is highly variant through time; hence, the percentage of live coral coverage also significantly varied compared to the earlier data of 2001 and 2015 (Shanmugaraj et al 2013;ENVIS 2015).…”

“…In the present study, SST ranges between 29.00°C-35.80°C during January and May, causing severe coral bleaching during summer (Figure 7). During 2016 coral bleaching, the temperature ranged between 30°C-34°C which caused 71.48% of corals to bleach in PB and 46.04% of coral bleached in GoM (Krishnan et al 2018). However, a similar result was found in the present study, where the Tuticorin group of Islands represents a high number of bleached corals than other areas of GoM, followed by PB (Figure 5).…”

Incursion of killer spongeTerpios hoshinotaon the coral reefs of Lakshadweep archipelago

“…Moreover, reports of turf algae being a dominant component in the atolls 17 might indicate towards a faster transition. Globally Elevated SST is a major threat to coral reefs 19 , and the reefs of India 20,21,22 including the atolls 23 are no different. With reports indicating that elevated SST has already depleted the coral ecosystem of Lakshadweep which was evident during 1998 17 , 2010 23 and 2016 19 mass bleaching events, it can provide an opportunity for sponges to invade 24 .…”

Incursion of the killer sponge Terpios hoshinota Rützler & Muzik, 1993 on the coral reefs of the Lakshadweep archipelago, Arabian Sea

“…Moreover, reports of turf algae being a dominant component in the atolls (Arthur et al 2005) might indicate a faster transition. Globally Elevated SST is a major threat to coral reefs (Hughes et al 2018), and the reefs of India (Edward et al 2018;Krishnan et al 2018;Raj et al 2018b) including the atolls (Vinoth et al 2012) are no different. With reports indicating that elevated SST has already depleted the coral ecosystem of Lakshadweep, which was evident during 1998 (Arthur et al 2005), 2010 (Vinoth et al 2012), and 2016 (Hughes et al 2018) mass bleaching events, it can provide an opportunity for sponges to invade (Bell et al 2013) .…”