Spatio-temporal Mapping to Investigate Coral Bleaching in Andaman and Nicobar Islands, India Using Geoinformatics

Andaman and Nicobar islands with vast variety of mostly endangered coral species are witnessing gradual coral bleaching. The present study focussed on temporal monitoring of various corals disposition along with impact of bleaching in two (North Reef and North Sentinel) islands of Andaman and Nicobar during the year 2010 and 2019. Floating algae index (FAI) and turbidity mapping was performed to evaluate the impact of excess macro algae on the coral reefs. The temporal coral mapping revealed that sand over reef, reefward front and exposed reef flat exhibit decrease by 2.23%, 18.55% and 33.86%, whereas algae over reef increased by 28.84%, respectively, in North Reef island. In case of North Sentinel island, exposed reef flat, sand over reef and reefward front decreased by 37.78%, 9.05%, 37.89%, whereas algae over reef increased by 55.81% during the observation period. FAI showed that in both islands concentration of macroalgae increased from year 2010 to 2019. Highest SST recorded for North Reef island was 35 °C in year 2017, whereas for North Sentinel island the highest value was 35 °C for year 2016. Turbidity values (11.86–44.53 NTU) clearly indicated pronounced effect of sedimentation and tourism activities in North Reef island which is corroborated by higher coral mortality conditions (24.70%) as compared to North Sentinel island (19.88%) reflecting increased bleaching on North Reef island. Accuracy assessment for coral classified image has been performed, for North Reef island overall accuracy of classified image for 2010 and 2019 is 86% and 84% for North Reef island, whereas for North Sentinel island overall accuracy of classified image for 2010 and 2019 is 83% and 82%.