ASSESSMENT OF CORAL BLEACHING DUE TO THERMAL STRESS OVER INDIAN OCEAN

Coral reef is an endangered species among the coastal ecosystems. It can act as a rainforest; forms an ecosystem; provide habitat; protect coast from waves; contribute in carbon sinking and attract tourists along the coast. The fragile coral reefs are highly sensitive to environmental variations (temperature, salinity, turbidity, etc.) and anthropogenic activities. Among the above, temperature is the major factor that can affect corals to a large extent. Therefore, it is important to assess the coral bleaching due to an abnormal rise in Sea Surface Temperature (SST). Current study is an attempt to quantify the intensity of coral bleaching using Marine Heat Wave (MHW) based on persistent SST over 90 percentile in the Andaman environs during April to May, 2010. The contiguous degree of MHW is a dictator of thermal stress, which is non-conducive to corals can lead to bleaching. In this study the relationship was established between MHW and In-Situ observations to estimate the Percentage of Coral Bleaching (PCB) on a synoptic scale. Extent and PCB can be calculated only based on MHW by using the estimated slope value 1.36 and intercept value -13.957. Further, the relation between the ratio index value derived based on the ratio of Remote Sensing Reflectance (Rrs) values of bands 412 & 531 nm and PCB to estimate the coral bleaching threshold (2.5). Significant correlation between Rrsratio index and PCB recorded is 0.82. The extracted threshold limits 2.5 ratio index can be used to confirm bleaching and values above this can categorize the coral bleaching intensity. The approach used in the current study enhances the capabilities of the operational coral reef monitoring programs and researchers.