Invasive Species Threaten Africa's Wetlands

NAIROBI, Kenya, February 5, 2003 (ENS) - Invasive species are devastating Africa's wetlandss, crowding out native species and costing billions of dollars in environmental and economic damage, warns a new report from international conservation groups. The groups have released a booklet describing the seven worst offenders, hoping to draw attention to the problem and promote ways of controlling - and perhaps profiting from - the invaders.

The beautiful, large purple and violet flowers of the South American water hyacinth make it a very popular ornamental plant, but it is also considered one of the worst aquatic weeds in the world. The invasive water hyacinth has inflicted enormous environmental and economic damage on Lake Victoria, among many other places in Africa and around the world.

Water hyacinth is one of the seven worst alien wetland invaders featured in the booklet "Invasive Alien Species in Africa's Wetlands," released today in Nairobi by IUCN - The World Conservation Union, together with the Ramsar Convention on Wetlands of International Importance and the Global Invasive Species Programme (GISP).

South American water hyacinth on Lake Victoria in Africa. This South American native is one of the worst aquatic weeds in the world, growing so rapidly that it can block waterways and crowd out other plants and wildlife. (Photo by Geoffrey Howard, courtesy IUCN)

Biological invasion is considered one of the greatest threats to biodiversity, second only to habitat loss and degradation. Invasive species can have devastating impacts on natural habitats and on the economy.

The economic damage inflicted worldwide by invasive alien species has been estimated at US$400 billion per year.

Invasive alien species are those that occur outside their natural range and threaten the existence of native plants and animals. These aliens can be plants, animals or microorganisms that are introduced intentionally for economic or agricultural purposes, or accidentally, through tourism, travel or trade, or when domestic animals become feral. Whatever the case, invasive alien species proliferate very quickly and, without controls such as their native competitors, predators, parasites and pathogens, can cause major problems for their new ecosystems.

"Invasive Alien Species in Africa's Wetlands" introduces some existing alien invaders that affect aquatic ecosystems in Africa, and describes others that feared to be on their way.

Water hyacinths are also a problem in the United States, where they are damaging many of Florida's waterways. (Photo courtesy Florida Department of Environmental Protection)

Infestations of this weed literally block waterways, interfering with their use and preventing sunlight and oxygen from penetrating the water column and reaching submerged plants, thus reducing biological diversity.

The Louisiana crawfish was brought to Africa for aquaculture, but has escaped to make its home in many African wetlands. (Photo courtesy The Aquaculture Network Information)

The Louisiana crayfish escaped from aquaculture sites in Africa where it is bred to provide a specialty food. Adult crayfish can travel long distances across land, particularly in damp grass, and so spread from one wetland to another.

The Azolla or red water fern can completely carpet the surface of a waterway. (Photo credit unknown)

The mats also provide havens for mosquito larvae and bilharzias carrying snails, while preventing light from reaching submerged plants and animals.

While the common or mirror carp is popular with anglers and fish farmers, it can be a real problem when it escapes into wild rivers and lakes. (Photo courtesy Travel Fish Africa)

Large carp females are reported to lay as many as a million eggs, which makes them popular for fish farms, but also allows the escaped fish to rapidly populate a lake or stream. While the carp represents a valuable source of food for African communities, the booklet stresses that the negative environmental impacts of its introduction need to be addressed.

Pickerel weed is among the invasive plant species expected to soon become a problem for Africa's wetlands. (Photo courtesy South Florida Water Management District)

The publication also outlines some solutions to existing biological invasions and provides tips on traditional and new uses of these species.

"We hope that the booklet will help Africa in its efforts to counter the global threat posed by alien invasive species and will give this issue a more prominent place on the agenda of conservationists, economists and planners, and in the thinking of millions of people across the continent and worldwide," said Howard. "It is also a first step in the Ramsar process of recognising invasive species as extremely important in wetlands and needing attention in every Ramsar site."