Praveen Paul Joseph

At Thovalai, the bloom disappeared on October 12

Many fish species died in the impact

TUTICORIN: The Fisheries College and Research Institute, Tuticorin, made a detailed survey of the impact of the algal bloom between Kilakarai and Vethalai, and on the Appa Island, on Sunday.

The survey was made along 15 km, between Kilakarai and Thovalai. Plankton, water, soil and fish samples were collected and analysed to study the water quality and the microbial load species of fish.

On-site analysis

An on-site analysis indicated that the coastal waters, between the island and the mainland, had a heavy marine algal bloom of Noctiluca scintillans, a free-living non-parasitic marine-dwelling species of dinoflagellate that exhibits bioluminescence, and the coastal water was dark green in colour.

The damaged cells started swelling and sinking and formed scum of threads, floating on the water.

The water quality analysis revealed that the nutrient levels were generally high in this region.

While the biomass of Noctiluca scintillans was 5,424 cells a litre in the Kilakarai coastal water, it was 3,920 cells on the Appa Island.

At Thovalai near Periapattinam, the bloom disappeared in the evening of October 12 and copepod nauplii was found dominating, and the dissolved oxygen content increased to 4.24 ml a litre. The blooming of Noctiluca scintillans declined on Sunday, and the dissolved oxygen content was low, owing to the decomposition of the bloom cells on the Kilakarai coast.

Species killed

Eels, Squirrel fish, Hardy head, Grouper, Sea bass, Silver bellies, Parrot fish, Rabbit fish and Gobids were some of the species killed in the impact of the bloom.

They were mostly resident of coral reefs. An analysis of the dead fish indicated gill chocking, and the low level of ammonia triggered their death. The bloom normally lasts 14 days, and the situation indicates that it may recede in 3-5 days.