Assessment of coral reef thermal stress over India based on remotely sensed sea surface temperature

Abstract

Sea Surface Temperature is a critical physical attribute of coastal marine habitats. Remote sensing from satellite is the most widely used approach for monitoring the stress on coral reef ecosystems on large scale. Regional coral bleaching monitoring framework has been applied in five major Indian coral reef regions to investigate the threats. Degradation of coral reefs is a major environmental problem worldwide. ENSO (El Niño Southern Oscillation) event is one of the extreme climate change event, which elevate Sea Surface Temperatures (SSTs) of tropical oceans. This warming of SST increases the level of thermal stress on coral reefs. Coral reefs are the most sensitive ecosystem of all coastal ecosystems due to temperature change and exhibit bleaching when SST exceeds their normal summer maxima and remain high for more than 28 days. SST data from NOAA OISST v2 over period from 1982 to 2018 (37 years) were used for this study. Coral bleaching indices have been observed over five major Indian coral reef regions. Bleaching Threshold (BT), Positive SST Anomaly (PA) and Degree Heating Week (DHW) are commonly used indices for calculating thermal stress on the coral reefs computed from satellite-derived SST data. The BT value for each regions based on the long-term SST data analysis and found different. These thermal stress analyses over India were found close with the recorded mass coral bleaching events during 1998, 2010 and 2016. In addition, this study included calculating the thermal stress over India during Mass Coral Bleaching years.

Keywords:

• Coral bleaching
• bleaching threshold
• positive anomaly
• degree heating weeks

Acknowledgements

The authors are thankful to the Director, Shri D.K. Das, Deputy Director, Dr. Raj Kumar and Division Head, Dr. Bimal Kumar Bhattacharya, Space Applications Centre, ISRO for their valuable suggestion, guidance and support towards this study. The authors also thank National Oceanic and Atmospheric Administration (NOAA) for providing respective SST data in the public domain. The first author is grateful for supported by a fellowship and lab facilities from the Space Applications Centre, ISRO. The authors express thanks to Dr. R. P. Singh, Head, Land Hydrology Division (LHD), SAC and GEER foundation, Gandhinagar for his constant encouragement and support.