The Indian coastline is home to an ancient and diverse coral reef system that provides natural habitat for diverse marine underwater ecosystem. Also, they hold importance in fisheries, tourism and as a repository of medicinal, agronomical and industrial products.

A team of Indian researchers has warned that rising sea temperatures due to climate change could put these wondrous underwater systems under peril. Their study, which analysed data of sea surface temperatures since 1982, has found that three mass bleaching events occurred in 1998, 2010 and 2016, impacting five major Indian coral reef regions, in Andaman, Nicobar, Lakshadweep, Gulf of Mannar and Gulf of Kachch. Oceans act as massive sinks for the greenhouse gases emitted by anthropogenic activities.

However, as they absorb them, the oceans warm up and there are changes in the seawater chemistry.

Corals are sensitive to temperature changes, which affect photosynthesis and calcification of their structures, making them prone to diseases and even death.

“Sea algae and corals share a symbiotic existence in the ocean.When the sea waters turn warm in summers and remain so for more than 28 days, the corals experience thermal stress. Due to this, the corals expel the algae residing in their tissues, and turn colourless or bleach,” explained Mohit Arora from Space Application Centre (SAC), Ahmedabad, and first author of the study, while speaking to India Science Wire.

For their study, the team utilised the sea temperature data from the National Oceanic and Atmospheric Administration (NOAA)’s Optimum Interpolated Sea Surface Temperature database and analysed them for the period from 1982.

They used daily computation and index parameters obtained from advanced satellite monitoring data under NOAA’s Coral Reef Watch. By analysing sea surface temperature patterns, the thermal stress on coral reefs and corresponding bleaching indices were computed based on information on magnitude, duration of thermal stress and intensity experienced in these regions.

The different regions experienced hottest summers at different times, with Andaman, Nicobar and Gulf of Kachch being severely affected in 2010 while Lakshadweep and Gulf of Mannar experienced a similar fate in 2016.

A coral bleaching alert report protocol developed by SAC recorded that the years 1998, 2010 and 2016 witnessed mass bleaching in the five coral reefs. They observed that Andaman, Nicobar and Gulf of Kachchh regions recorded an ‘alert level-2’ warning status in 2010, while the Gulf of Mannar recorded a level-1 alert in 2016. Although coral reefs are known to recover from bleaching in a decade or two, the severity of the bleaching event could overwhelm them and hamper their ability to recover.

“There is a likelihood of high-intensity coral bleaching events in the future also.Our study will be helpful to marine biologists and can be used for early warning of coral bleaching in future,” said Arora.

The team comprised Mohit Arora, Nandini Ray Chaudhury, Ashwin Gujrati (SAC); and Ramesh Chandra Patel (Kurukshetra University). The findings have been published in Current Science.

(India Science Wire)

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