The World Conservation Union recently released a report, Alien Invasive Species in Africa’s Wetlands, claiming that invasive alien species are costing Africa billions of dollars annually. Such species include water hyacinth, water lettuce, water fern, Louisiana crayfish, and common carp.
The water hyacinth, for example, grows extremely quickly and harms wetland ecosystems by blocking sunlight and oxygen from bodies of water. Similarly, the water fern is a haven for mosquitoes and snails that carry bilharzia (a tropical disease that infects up to 300 million people annually).
Most of the invasive species were introduced accidentally through tourism and trade. Worldwide, the World Conservation estimate total economic costs of invasive alien species at $400 billion.
Source:
Alien species ‘cost Africa billions’. Alex Kirby, The BBC, February 5, 2003.
IUCN launches new publication on alien invasive species. Ramsar.Org, February 2003.