The Hindu : Kerala News : Fish kill traced to red tide phenomenon

Online edition of India's National Newspaper
Tuesday, Sep 14, 2004

Kerala

Kerala

Fish kill traced to red tide phenomenon

By T. Nandakumar

THIRUVANANTHAPURAM, SEPT. 13. A `red tide bloom' of toxic plankton triggered by the discharge of raw sewage into the sea, was responsible for the mass mortality of fish reported from the Kollam coast last week, scientists have reported.

A team of scientists from the Centre for Earth Science Studies (CESS) who carried out a battery of tests in the coastal areas, came to the conclusion that large quantities of sewage flushed out during the rain, had created a nutrient-enriched marine environment conducive for the blooming of toxic plankton.

Plankton

The team led by P.P. Ouseph identified the organism as Coclodeneum, a species belonging to the dinoflagellate group of marine plankton. The scientists reported that the near-shore current towards the north had carried the red tide from Thankassery to Neendakara, along a wide swathe measuring about five sq.km.

The CESS director, M. Baba, said the fish had died in large numbers after consuming the toxic plankton. "A red tide bloom also depletes the waters of oxygen content. As a result, several species of fish, especially the bottom-dwelling ones, are deprived of oxygen and are eventually killed," he said.

Potent toxins

Red tides are caused by the abundance of dinoflagellates, which are known for producing potent toxins when they occur in large numbers during a bloom. The concentration of planktons changes the colour of the seawater to red.

An essential part of the food chain, the planktons introduce their toxins into several species of fish.

On the wane

Water samples taken from the coast on Friday revealed that the dinoflagellate concentration was as high as 10 lakhs per litre. "It came down to 3 lakhs per litre on Saturday, confirming the fact that the phenomenon is on the wane", Dr. Baba said.

The team reported that the plankton was also responsible for the seawater fluorescence reported by fishermen. The nauseating smell experienced by residents in the coastal areas has been attributed to the strong winds, which carried the stench of a large number of rotting fish floating on the sea surface.

Discounting apprehensions over consumption of fish, Dr. Baba said the red tide had diminished considerably over the past several days.

"The system has started stabilising. There is no cause for alarm."

He, however, added that the phenomenon was bound to repeat itself in the absence of a mechanism to check discharge of untreated sewage into the sea. "It is a clear violation of the Coastal Regulation Zone (CRZ) norms", he said.

The red tide bloom was reported from coastal areas of the Thiruvananthapuram district in 1997 and 1999.

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