Algal bloom leaves coral reefs bleached

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HARD HIT: An underwater picture of a bleached coral formation at the Mulli island near Keezhakarai in the Gulf of Mannar.
HARD HIT: An underwater picture of a bleached coral formation at the Mulli island near Keezhakarai in the Gulf of Mannar.

C. Jaisankar

A few colonies recovering after the temperature became normal, says expert

RAMANATHAPURAM: The algal bloom in the Mandapam and Keezhakarai group of islands of the Gulf of Mannar has left the coral reef colonies in the Vazha and Mulli islands bleached.

According to the preliminary report of an underwater study carried out by the Sugandhi Devadasan Marine Research Institute, Tuticorin, along the seaward side of the shallow waters of the Vazha island, where the depth is 0.5-0.75 metres, 20-25 coral colonies of table corals (Acropora cytherea) and branching corals (Acropora nobilis) and (Monitpora digitata) have been bleached.

In the Mulli island, 10 small colonies of corals have been fully bleached in the shallow waters. The corals that are in depth below 1 metre have been partially bleached.

The bleaching, says the report, is due to the elevated sea surface temperature (31 C), which is very abnormal in October. The report was submitted to V.K. Melkani, Chief Conservator of Forests, and Director, Gulf of Mannar Marine Biosphere Reserve Trust.

J.K. Patterson Edward, Director, Sugandhi Devadasan Marine Research Institute, told The Hindu on Tuesday that a few colonies started recovering after the temperature became normal.

Along the seaward side, where the depth ranges from 1 metre to 2 metres, the density of dead algae was high for 1.5 km from the island towards the sea.

However, there was no impact on the coral reefs and seagrass beds in the Mandapam group of islands. But the reef and seagrass areas in the Vazhai, Thalaiyari and Mulli islands would have to be monitored because of the large-scale decomposition of bloom that led micro-organisms to flourish.

Coral disease

Mr. Edward said the settlement of dead cells, if not washed away from the reef and seagrass areas, would pose further stress on the corals and sea-grass.

In the Gulf of Mannar, the prevalence of coral disease was increasing in recent days, he said, to drive home the need for regular monitoring and effective management. The seasonal circulation factors and the nutrient enrichment of coastal waters by human activities were responsible for the proliferation of algal bloom.

Mr. Melkani said the recommendations would be implemented.

The changes in the sea would be monitored for the next 15 days.

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