Pressure on aquatic ecosystem

Introduction of invasive alien fish species has depleted the aquatic biodiversity of the State

THIRUVANANTHAPURAM 18/03/2008-----Green Cover: A profusion of water weeds covers the Aakulam lake in Thiruvananthapuram. A scene from the Aakulam bridge.................................Photo:C_Ratheesh kumar

The aquatic biodiversity in Kerala is also facing a serious threat from biological invasion. Proliferation of invasive water weeds and exotic species of fish has disrupted the riverine and lake ecosystem in the State and depleted native aquatic biodiversity, threatening the livelihood of inland fishermen.

Water hyacinth is one of the most threatening invasive species in Kerala, says A. Biju Kumar, Head, Department of Aquatic Biology and Fisheries, University of Kerala.

“The annual economic loss due to the proliferation of this waterweed in lakes and waterbodies would be to the tune of hundreds of crores,” he says.

Listed as one of the 100 most dangerous invasive alien species in the world, it was introduced to India as an ornamental plant for cultivation in ponds. By crowding out native aquatic plants, the fast growing weed native to South America dramatically reduces biological diversity in aquatic ecosystems.

The inland waterbodies in Kerala also play host to three other aquatic invasive plants and 12 species of invasive fishes.

Mozambique Tilapia, introduced for commercial aquaculture, is the most common and widespread invasive fish in the State, found in 70% of the rivers, 80% of the perennial ponds and all the lakes except Sasthamkotta.

Nile Tipalia has also established good populations in rivers. Considering the damage caused to native fish and biodiversity, the Tilapia is termed a `biological pollutant’ by the Food and Agricultural Organization. Known for its aggressive behaviour and capability to survive in fresh and brackish water, it competes with native fish for food and space.

Guppy (Poecilia reticulata), introduced for mosquito control, is present in all waterbodies across the State and also in wildlife sanctuaries. The fast-breeding species feeds on the eggs of native fishes and is believed to carry parasites that can be fatal for other aquatic organisms.

Many inland waterbodies in the State are now dominated by sucker fish (Ptergoplichthys), a hardy exotic aquarium species that is capable of hybridisation.

Earlier this year, the government imposed a ban on the farming of the carnivorous African catfish (Clarias gariepinus) which had proliferated to dangerous proportions, posing a threat to local aquatic species. Experts highlight the need for selective culling to destroy existing stocks.

Pointing out that early detection and management are key to controlling bioinvasion in aquatic ecosystems, Dr.Kumar moots legislation to prevent the release of alien species into natural waterbodies, along with restrictions and ban on import and guidelines for management of invasive alien species. He also calls for an awareness campaign involving citizen scientists to deal with the issue.

The recent discovery of colonies of invasive snowflake coral ( Carijoa riisei ) on rocky reefs off the Thiruvananthapuram coast has triggered concerns over the marine ecology of the region.