Rising temperatures to blame for coral catastrophe this year

A sustained rise in water temperature this year has wreaked havoc on coral reefs, wiping out 16.2 per cent of corals in the Gulf of Mannar (GoM) — the highest yearly mortality rate for the past few decades.

The reef research team of the Suganthi Devadason Marine Research Institute (SDMRI), which has been conducting underwater surveys since the end of March in the GoM region, covering all the 21 islets and Palk Bay, has found that the live coral cover in the Gulf of Mannar has declined from 38.86 per cent in 2015 to 22.54 per cent this year.

The destruction of the corals was the result of a phenomenon called ‘coral bleaching’, which occurs when water temperatures rise for a sustained period of time. Research shows that there had been 26.5 per cent coral bleaching in Mandapam and 30 per cent each in Kilakarai and Thoothukudi group of islets during the period from April to June, with only a small proportion of corals recovering post the temperature surge.

“In general, the bleached corals recover once the temperature falls, but severe mortality was observed even in July and August, notwithstanding a drop in temperature,” Mr. J K Patterson Edward, director of SDMRI, told

The Hindu , sharing the details of the survey.

The Mandapam group of islets bore the brunt with 22.2 per cent mortality, followed by 17.2 per cent in Kilakarai and 9.2 per cent in Thoothukudi after the fall in temperature, he said, adding that fast-growing life forms such as branching, foliose and digitate types of corals, belonging to the ‘pocillopora’, ‘acropora’ and ‘montipora’ species were the hardest-hit in Mandapam and Kilakarai groups.

The affected species included Acropora formosa, A. intermdeia, A. nobilis, A. cytherea, Montipora divaricata, M. digitata, M. foliosa and Pocillopora damicornis.

“All coral recruits (young corals) were found dead. A few branches in large colonies are alive and are expected to recover in two to three years, provided there is a conducive environmental condition,” Mr. Patterson said.

The maximum temperature was 33 degree Celsius in all reef areas and though the bleaching was high in Thoothukudi group (30 per cent), mortality was comparatively low (9.2 per cent) due to high recovery (20.8 per cent), he said.