Relationship between coral bleaching and large-scale oscillations in the Lakshadweep archipelago

The coral reef ecosystems in the Lakshadweep Sea are among the least studied due to the dearth of in situ measurements. The objectives of this study were to compare the remote sensing datasets with the available in situ measurements and confirm the reliability of the former for further studies in this region. The study also examines how the sea surface temperature and salinity triggered coral bleaching during El Nino southern oscillation (ENSO)/Indian Ocean dipole (IOD) events. We found that satellite observations of sea surface temperature (r = 0.94) and salinity (r = 0.81) correlated well with in situ measurements. Such a high degree of correlation enabled us to analyse satellite data for inter-annual variations like ENSO and IOD. In the study area, coral bleaching due to salinity variation was found to be negligible. The study delineates a coral bleaching threshold temperature and the prevalence of such warm waters in the coral environment. Analysis revealed a mass coral bleaching peak during the El Nino event in 2016, with a maximum prevalence of 78 days. Similarly, significant coral bleaching events were observed in 2010 (El Nino; 63 days) and 2019 (PIOD; 56 days). Maximum temperature was noticed during the spring inter-monsoon (March to May). But from 2015, intense warming in the coral region was also noticed in the fall inter-monsoon (October). Combined with global warming, the threat of thermal stress to corals may continue in the long term, which will negatively impact the health of reef ecosystems.