Thermal stress impacts corals in Indian waters

Updated - October 18, 2016 12:45 pm IST

Published - May 28, 2016 05:52 pm IST

During the last couple of months, an increase in sea surface temperatures was observed in these waters. Photo: Special arrangement

During the last couple of months, an increase in sea surface temperatures was observed in these waters. Photo: Special arrangement

Coral ecosystem thriving in the Indian waters has come under severe stress with instances of coral bleaching being reported from islands of Lakshadweep and some parts of Andaman.

It is the thermal stress in the form of increase in Sea Surface Temperature (SST) during April that has proved disastrous for the corals.

While bleaching has been widely reported in the coral islands of Lakshadweep, some isolated incidents were reported from Andaman. Joint observations carried out by the National Institute of Ocean Technology, Chennai, and the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, confirmed the developments, said Satheesh Shenoi, director of the INCOIS.

Sea surface temperature

During the last couple of months, an increase in the Sea Surface Temperature was observed in the waters around the Andaman Islands, the Gulf of Mannar, and the Lakshadweep Islands. Following the observations, warning was sounded in these areas for coral bleaching. The in-situ observations carried out at North Bay, South Andaman revealed the primary signs of bleaching, according to a communication from the INCOIS.

“Coral bleaching takes place when the symbiotic relationship between algae (zooxanthellae) and their host corals breaks down under certain environmental stresses. This results in the host expelling their zooxanthellae. In the absence of symbiotic algae, the corals expose their white underlying calcium carbonate coral skeleton and the affected coral colony becomes pale in colour. Coral bleaching can be activated and persist during varied environmental stresses,” explains a scientific document released by the Centre.

The SST was in the range of 32 degree Celsius when in situ temperature observations were made during the last week of April in Andaman coast. However, the rain following the development of a depression in the Bay of Bengal has brought down the SST thereby averting the massive incidents of bleaching, Dr. Shenoi explained.

There existed a strong trend for bleaching but not to an alarming level and only a few species were found to be vulnerable to the trend, he explained.

In Lakshadweep, bleaching was reported in the water around the islands of Kavarathy, Agathy and Bangaram. The damage to the coral ecosystem was reported as deep as 30 metres, according to Idrees Babu, a scientist of the Department of Science and Technology, Lakshadweep.

The SST in the Lakshadweep waters rose to 32 degree Celsius against the normal temperature of 25 degree Celsius. There has not been much rain in region except the scattered showers, said Mr. Babu.

The Lakshadweep region witnessed a massive destruction of corals in 1997 when around 85 per cent of the coral reef was destructed.

Coral regeneration

Amidst growing concern about the impact of coral bleaching, scientists have also brought out some good news from the ocean depths of Andaman. The branching corals that were destructed during the 2004 South Asian tsunami have started regenerating in the region. The impact of bleaching would be different in different species and some may take 10 years or longer to regenerate, Dr. Shenoi pointed out.

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