Special Correspondent

International Day for Biological Diversity observed today

Thiruvananthapuram: Proliferation of invasive water weeds and exotic species of fish has played havoc with the ecosystem of the Veli and Aakkulam Lakes and the feeder canals, threatening the livelihood of inland fishermen and affecting backwater tourism.

Studies by the Department of Aquatic Biology and Fisheries, University of Kerala, show almost zero oxygen levels in the lakes round the year. Hardly any species survive in the water.

The threat to the water bodies in the State assumes importance in the context of the theme of this year’s International Day for Biological Diversity (which falls on Friday) namely, ‘Invasive alien species: a threat to biodiversity.’

Biological desert

“The invasion of the two lakes by water hyacinth has turned the ecosystem into a biological desert. Pollution of the water has worsened the situation,” A. Biju Kumar of the department said. Water hyacinth is the most threatening invasive species in Kerala, observed Dr. Biju Kumar. “The annual economic loss due to the proliferation of this water weed in lakes and water bodies in the State would be to the tune of hundreds of crores, even though no one had ever made a precise estimate of this,” he said.

Water hyacinth, a fast-growing plant with populations known to double in as little as 12 days, blocks waterways, limiting boat traffic, swimming and fishing.

The weed prevents sunlight and oxygen from reaching the water column and submerged plants. By crowding out native aquatic plants, it dramatically reduces biological diversity in aquatic ecosystems.

Listed as one the 100 most dangerous invasive alien species of the world, this aquatic weed native to South America, was introduced to the country as an ornamental plant for cultivation in ponds because of its beautiful, large purple and violet flowers. Today, it invades more than 50 countries in five continents.

The sand bar at the mouth of Veli Lake hampers natural flushing by saline water, facilitating domination of the system by water hyacinth. “As chemical removal of invasive weeds is ecologically not advisable and biological control has been successful only in laboratories, a permanent system should be evolved for the mechanical removal of water weeds by networking communities and NGOs, coupled with allowing frequent natural flushing of the system by removing the sand bar,” Dr. Biju Kumar said.

Another problem encountered by the fishermen in Veli Lake is the domination of the exotic fish, Tilapia (Oreochromis mossambica). Considering the damage caused to native fish species and biodiversity, Tilapia is termed a ‘biological pollutant’ by the Food and Agriculture Organisation.

The canal systems connected to the lakes are now dominated also by the hardy exotic species, sucker catfish (Plecostomus multiradiatus), which could have escaped from aquariums.

The Kerala State Biodiversity Board is organising a national seminar here on May 22 in connection with the biodiversity day observance.