Bleaching Stress on Indian Coral Reef Regions during Mass Coral Bleaching Years using NOAA OISST Data

Abstract

Coral reefs are one of the most ancient, highly productive marine bio-diverse ecosystems on earth. They are threatened to collapse under rapid climate change. ENSO is an extreme climate change event which elevates sea-surface temperature (SST) of tropical oceans. This elevated SST increases the level of thermal stress on coral reefs. Also, coral reefs are the most sensitive among all ecosystems due to temperature change; they exhibit bleaching when SST exceeds normal summer maxima and remains high for more than 28 days. Bleaching threshold, positive SST anomaly and degree heating week (DHW) are commonly used indices for calculating thermal stress on coral reefs. The major coral reef regions in India are Andaman, Nicobar, Lakshadweep, Gulf of Mannar and Gulf of Kachchh. SST from NOAA OISST v2 highresolution daily dataset at 0.25° global grids from 1982 to the present was used for the present study. Here, we focus on the variations in SST experienced by Indian coral reef regions during known mass coral bleaching (MCB) years, viz. 1998, 2010 and 2016. The year 2010 recorded the highest thermal stress for Andaman, Nicobar and Gulf of Kachchh regions, and the year 2016 was severe for Lakshadweep and Gulf of Mannar regions. In 2010 Nicobar was observed to be the most vulnerable according to DHW index.