Climate Change

SDMRI RRT started regular reef monitoring in Gulf of Mannar since 2005 and significant rise in the surface water temperature during summer and subsequent coral bleaching and mortality are being continuously observed.

Major reef areas in the Gulf of Mannar are shallow, between 0.5-6 m depths, and so high temperature prevails throughout the year and the corals seem to be acclimatized to such situation.

The bleaching of corals is normally noticed from mid April and high temperature exists for about a month from the end of April. Massive corals especially Porites sp. are the first to be affected and the other dominant coral species partially or fully bleached are Acropora cytherea, A. formosa, A. intermedia, A. nobilis, M. foliosa, M. digitata and Pocillopora damicornis. Branching corals recover faster than the massive corals; the fastest recovered coral size groups were 40 to 80 cm and 80 to160 cm. The pattern of effect is almost similar on the reefs every year except the modest fluctuations in the temperature levels.

Temperature level over 31.0ºC causes bleaching and the corals start to recover when the temperature level falls. Depends on rainfall and winds, recovery begin during June-July and completes in 1-4 months.

Significant coral mortality was only recorded in 2010 when elevated temperature (32.2 to 33.20C) persisted for four months (April to July). An estimated amount of 9.99% live coral colonies bleached and more than 50% mortality among the bleached colonies. The coral species which died because of bleaching include Pocilopora damicornis, Acropora formosa, A. intermedia, A. nobilis, A. cytherea, Montipora digitata, Montipora foliosa, Favia sp. and Echinopora sp. Recovery was primarily noted in the partially bleached colonies of coral species species, Pocillopora damicornis, Acropora formosa, A. nobilis, A. cytherea, Montipora foliosa and M. divaricata.

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