The bleaching is up to 83.6 per cent and has happened due to the impact of the El Nino event and increased sea surface temperature in 2016.
“The detailed studies during pre and post bleaching surveys by ZSI scientists found that 23.58 per cent of the live cover were lost due to this massive bleaching in 2016 in the Andamans,” she said on Wednesday.
Besides, a recent publication of Global Coral Reef Monitoring Network ‘Status of Coral Reefs of the World: 2020’ reported a gradual decrease in the live cover of hard corals from 32.3 per cent in 1978 to 29.5 per cent in 2019, Banerjee said.
Another study of 2021 pointed at the rapid decline in coral calcification, mostly due to heat stress.
The destructive impacts of El Nino are well documented through the bleaching events across the world like the loss of 16 per cent of the world’s reef cover in 1998 along with the greatest mortality report of 70 per cent from the Indian Ocean region. There were reports of 93 per cent bleaching of the coral colonies followed by 22 per cent of dead corals from the Great Barrier Reef in 2016, Banerjee said.
The ZSI director iterated that these vulnerable ecosystems are on the verge of facing frequent threats whereas their services towards sustainable and healthy reef habitats, coastal protection, development of tourism and recreational benefits and providing economic support of the coastal population for their sustainable livelihood are exceedingly high.
“It is high time for us to make ourselves aware enough to conserve this fragile ecosystem before their mass extinction,” she added.
A total of 83.6 per cent scleractinian corals or hard corals was recorded to have been bleached from the Bay islands from April to May 2016. It was recorded that a total of 83.6 per cent of the scleractinian corals were bleached during this period.
Maximum bleaching of 91.5 per cent was recorded in the Andaman Sea region of South Andaman, while it was the minimum in North Andaman region where it is 83.2 per cent.
There was no record of bleaching from the Bay of Bengal coast of North and Middle Andaman, but the Bay of Bengal coastal areas of South Andaman displayed 74.2 per cent of bleached corals, the study said.
The research was made up to the depth of 40 m and it was found that bleaching was recorded up to the maximum depth of 30 m. The highest impact of bleaching was recorded at the depth range of 0-6 m followed by 6-15 m.
ZSI scientist Tamal Mondal of the Andaman and Nicobar Regional Centre stated that the recovery of bleached corals was noticed from July to December 2016 and based on studies, it was found that a mean recovery of 23.69 per cent was recorded among the bleached corals of the Andaman group of islands.
The maximum and minimum recoveries were recorded in North Andaman region of the Andaman Sea coast (29.25 per cent) and the South Andaman of the Bay of Bengal coast (19.18 per cent), respectively.
Mondal said that it is assumed that the luxuriant mangrove ecosystem is expected to buffer the heat waves and keep the corals of North and Middle Andaman unbleached and healthy, although it is not yet proven by any experimental studies.
Mangroves are known to purify water by absorbing nutrients from runoff as well as harmful algal blooms to keep them clear, which is a prerequisite for healthy coral reef ecosystems. Mangroves are also prime organisms that absorb carbon from carbon dioxide.