Photosynthetically active radiation, a critical parameter for mass coral bleaching in the North Indian Ocean

The Gulf of Mannar (GOM) and Kadamat Island (KI) are two major coral reefs that were severely bleached en masse in the North Indian Ocean (NIO) during 1998. Mass coral bleaching took place once again in NIO during 2002, which severely affected the GOM corals but not the KI corals. This contrasting phenomenon prompted us to re-examine parameters such as surface sea temperature (SST), photosynthetically active radiation (PAR), hotspots, heat content, sea-surface height anomaly (SSHA) and North Indian Ocean Dipole (NIOD) events. The analysis indicates that the above mass bleaching events are associated with high PAR (47 Einstein/m(2)/day) with minimum SST of 30 degrees C, which was probably critical for mass bleaching in NIO during 1998 and 2002. However, the above bleaching events do not show any direct link with SSHA, hotspots and NIOD.