Bleached corals will recover only if the temperature level comes down, says expert

The coral reef wealth of the Gulf of Mannar, which is being conserved through joint efforts of various governmental, non-governmental and research agencies, is now facing a different kind of threat — global warming and consequent climate change.

Coral reefs, known as rain forests of the sea, are a source of food security and livelihood options for hundreds of millions people, coastal defence and tourist hotspots. The Gulf of Mannar (GoM) is one of the four important coral reefs in India and thousands of artisanal fisher folk are dependant on fishery resources from this reef area.

Though direct human impacts have resulted in vast destruction of the reef area and associated flora and fauna for the last three or four decades, strengthened enforcement of law, inclusion of corals under Schedule I of Wildlife Protection Act, 1972 and enhanced awareness among the coastal community of coral reef conservation have arrested the decay.

After the tsunami and various conservation and eco-developmental activities, coral mining was completely stopped in 2005 and there has also been a reduction in destructive fishing activities near the reef. These factors have resulted in the enhancement of live coral cover from 37 per cent in 2005 to 43 per cent in 2009 owing to stable substratum, initiation of coral restoration on six islands, successful reproduction and high coral recruitment.

However, the effect of global climate change is always a threat to the corals, as they are very sensitive, and also to the fish population associated with reefs. The impact of climate change was clearly visible in 1998 in the Indian Ocean with many reefs, previously regarded as near pristine, seriously affected. The corals of GoM were also affected in 1998.

Tuticorin-based Suganthi Devadason Marine Research Institute, affiliated to Manonmaniam Sundaranar University, has been regularly conducting coral reef monitoring in GoM since 2005 with permanent monitoring sites and annual bleaching has been observed during summer every year since 2005 owing to elevated sea surface temperature.

“The percentage of bleaching in live coral cover depends mainly on the wind, water currents, rainfall, turbidity and depth. The maximum affected corals are in the shallow waters – ranging from depths of 0.50 metres to 2 metres.

“This summer, the coral bleaching was observed from the second week of April when the average surface water temperature was between 29.1 degree Celsius and 33 degree Celsius in Mandapam; 29.3 degree Celsius and 33.1 Celsius in Keezhakkari ; and 29.3 degree Celsius to 33.6 degree Celsius in Tuticorin,” J.K. Patterson Edward, Director, SDMRI, told The Hindu. The overall percentage of coral bleaching is 10.6 on the Mandapam coast, while it is 7.5 and 9.3 on Keezhakkarai and Tuticorin coast.

The maximum bleaching of 12.50 per cent has been recorded on Shingle Island (Mandapam coast); 9.4 per cent on Appa Island (Keezhakkaari coast) and 14.7 per cent on Kariyachalli Island (Tuticorin coast).

The most affected species are branching corals such as like Acropora nobilis, A. formosa, A. cythera, Montipora foliosa, and Pocillopora damicornis and massive corals such as Porites solida and Favia pallida.

The partially bleached coral species are Porites lutea, Favia pallida, Favites abditta and Echinopora lamellose. The coral species such as Porites lichen, Goniastrea rectiformis, Favites abditta, Platygyra lamellosa, Hydnopora microconos, Symphyllia recta, Acropora intermedia and Montipora divaricata have started to bleach and if the temperature level prevails, they will be completely bleached soon.

Among the bleached coral colonies, 40 per cent are recruits; 35 per cent are of intermediate size; and 25 per cent are large colonies. The bleached corals are in stressful state. They will recover only if the temperature level comes down owing to change of climatic condition.

Wildlife Warder, Gulf of Mannar Marine National Park, M. Sundarakumar, said any external disturbance in the form of heavy trawling would destroy the already affected coral reef. “It is essential that the coral areas should not be disturbed by the fisher folk by any kind of illegal fishing and other activities such as trap fishing, trawling, seaweed collection, shore seine operation, ornamental fish collection etc. The Marine National Park authorities have also intensified the vigil in order to avoid any human disturbance in the reef areas,” Mr. Sundarakumar said.