A red alert

Phytoplankton bloom along the Indian coast threatens marine life

Published: Monday 31 January 2000

there is a new danger to the marine ecosystem: the occurrence of phytoplankton blooms that threatens the lives of molluscs, fish species, shrimps and whales.

Phytoplankton are unicellular, microscopic, free-floating marine plants. Their growth is influenced by sunlight, ocean currents, salinity, temperature and nutrients such as nitrogen and phosphorus. A phenomenal increase in their numbers could actually change the colour of water to red, brown or green. These species also secrete toxins, which accumulate in plankton-feeding fish and other animals.

In 1987, the death of a dozen humpback whales in Massachusetts was linked to red tides, called so because of the change in the colour of water to red. Widespread fish deaths in the Gulf of Mexico are also attributed to the presence of a dinoflagellate species (unicellular marine organism), Gymno dinium . Alexandrium , Dinophysics and Pseudoniyzschia are some of the other toxin-secreting phytoplankton species.

In India, harmful blooms have been reported from the east as well as the west coast. "In 1997, a species of Alexandrium caused a red tide near Thiruvananthapuram," says K Prabhakaran Nair, scientist at the Central Marine Fisheries Research Institute at Vizhingam near Thiruvananthapuram. Seven people died and over 300 were taken ill due to consumption of contaminated sea food in the coastal areas of Vizhingam and Poovar.

Scientific tests later attributed the contamination to saxitoxin ( stx ), a toxin secreted by Alexandrium . Consumption of food contaminated with stx resulted in numbness around the mouth, muscle weakness and even paralysis. "The illness is known as paralytic shellfish poisoning ( psp )," says Nair. stx disrupts the flow of sodium ions that are involved in the communication between muscle and nerve cells.

In addition to psp, other illnesses like dsp (diarrhetic shellfish poisoning), nsp (neurotic shellfish poisoning) and asp (amnesiac shellfish poisoning) have also been linked to red tide blooms.

A number of factors lead to phytoplankton blooms. In India, their occurrence has been linked to the monsoons. "Climatic changes induce nutrient-rich bottom marine waters to mix with warm surface waters," says Aravindan of the department of aquatic biology, University of Kerala. "When this happens, some phytoplankton species bloom," he adds. Anthropogenic activities also increase the occurrence of red tide. Rise in nutrients due to agricultural run-off, sewage, aquaculture wastes and pollution can also trigger such events.

At present, a study funded by the department of ocean development is monitoring the Indian coasts. If timely action is not taken in India, which has a lengthy coastline and high human population, the aftermath of such blooms may be devastating.

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