Differential bleaching patterns in corals of Palk Bay and the Gulf of Mannar

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 degrees C to 34.0 degrees 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.