Case Study: Water Hyacinth

One of the most dramatic and far-reaching invaders, the water hyacinth Eichhorina crassipes, threatens everything from fisheries, hydroelectric production, agriculture, human health, to the economy. It has been called the world’s worst tropical aquatic weed. A native to the Amazon basin, it has invaded 53 countries within 5 continents, sometimes taking over entire river and lake systems. It was introduced both intentionally and unintentionally, specifically to help purify water from waste treatment facilities and for use as an ornamental aquarium plant. It especially thrives in tropical areas, such as parts of Africa.

Lake Victoria, which borders Uganda, Tanzania, and Kenya, is the most dramatic example of the havoc water hyacinth can wreak on an ecosystem. First sighted in 1989, water hyacinth now covers ninety percent of Lake Victoria’s shoreline. This thick mat of water hyacinth competes with the native plants, fish, and frogs for oxygen, often causing asphyxiation and massive die-offs. The hyacinth, which is 92% water, also respires at an incredibly rapid rate, thereby dropping the lake’s water level.

The Lake Victoria Basin is home to some 30 million people with one of the fastest growing populations in the world. The region is sustained by its fisheries, with over half of the protein supply coming from fish. However, due to reductions in fish populations, tens of thousands of people have left their fishing livelihood and have emigrated to the city. For those who remain, it has become virtually impossible to navigate Lake Victoria with small fishing vessels due to the abundance of water hyacinth. The weed often clogs the pipes for the neighboring city’s water supply, and has occasionally threatened Uganda’s main generating station. One estimate claims the economic cost of this invasion to be $150 million each year. The mat of water hyacinth also hosts a new community of organisms, many of which are responsible for serious vector borne disease, not to mention increased contact of fisherman with dangerous organisms. There are increased reports of fatalities due to hippos and crocodiles, bites from rats and snakes, and malaria from mosquitoes, all of which find ample habitat and cover in the thick mats.

Unfortunately, this invader is not limited to one area. In southern China, the level of Lake Dranchi dropped dramatically from water hyacinth, the local climate grew noticeably more arid, and 38 of the 68 fish species in the lake were eliminated. Water hyacinth has overgrown dams in Zimbabwe, backing up enough water to burst them. California, Texas, Florida, and most southern states now suffer from the effects of water hyacinth, including clogged flood-control and irrigation systems as well as limited boat transport in waterways.

Manual or mechanical removal of water hyacinth and chemical control of the plant have proven difficult. Several species of biological control have been introduced against water hyacinth. The mottled water hyacinth weevil, Neochetina eichhorniae, was released in Florida in 1972 and the chevroned water hyacinth weevil, Neochetina bruchi, was released two years later. The Argentine water hyacinth moth, Sameodes albiguttalis, which retards growth in the early stages of water hyacinth mat development, was released and is now established in Florida, Louisiana and Mississippi, as well as in Australia, South Africa and Sudan.

-- Daou, A., "Grappling with Water Weeds in Mali", IUCN World Conservation, April 1997, p. 29

-- Bright, C., Life Out of Bounds: Bioinvasion in a Borderless World, Worldwatch Environmental Alert Series (New York, NY: Norton, 1998 pg. 89-92, 182)

-- Corn, M.L., J. Rowson, E.H. Buck, E. Fischer, "CRS Issue Brief for Congress-Harmful Non-Native Species: Issues for Congress  RL30123," (Washington, DC: Congressional Research Service, April 8, 1999)

Related Link:
-- ^{http://aquat1.ifas.ufl.edu/hyacin.html}