Transcript Aquatic (water) invasive species in Zimbabwe...download here

Chinhoyi University of Technology
Invasive Species Research and Management Unit
AQUATIC (WATER) INVASIVE SPECIES IN ZIMBABWE
Water hyacinth (Eichhornia crassipes (Martius)
Origin: South America in the Amazon Basin in northeastern Brazil, Venezuela, Guyana and Surinam .
Description: Floating aquatic weed that belongs to the
family Pontedereceae which is closely related to lily (
Liliceae) family.
Damage caused by the species: Grows rapidly and forms
thick impregnable mats that block navigation and deny
access to rivers and dams for fishing, tourism and
recreational uses. Severe infestations are associated with
high levels of pollution of water with industrial and sewage
waste. Water hyacinth displaces other species from the
ecosystem. Despite the introduction of biological weevils,
Neochetina eichhorniae and N. bruchi in Zimbabwe, it
remains the most problematic aquatic weed in Zimbabwe
Kariba weed or Giant Salvinia (Salvinia molesta Mitchell)
Origin: It is native in south-eastern Brazil and has spread throughout the
tropics and subtropics in the Americas, Africa and Asia.
Description: It is a free-floating aquatic fern belonging to the family
Salviniaceae. The fronds are 0.5–4 cm long and broad, with a bristly
surface caused by the hair-like strands that join at the end to form
eggbeater shapes. The bristles trap air, the “salvinia effect” , allowing
the fern to float on the water surface.
Damage caused by the species: The floating fern showed explosive
growth after the creation of Lake Kariba in 1985. By 1962 it covered 22%
of the Lake surface but later declined to a stable level of 10-15%.
Coverage declined again in 1973 to 5% and by 1980 only 1% of the lake
was coved by the fern. The decline was attributed to a biological control
agent, the Neotropical grasshopper, Paulina acuminata De Geer and
nutrient stress on the fern as other components of the ecosystem grew
and competed for nutrients (Marshall and Junor, 1981). Effective
biological control of the fern is now being accomplished by the
introduction of weevil, Cyrtobagous salviniae, into water impoundments
infested by the weed (Chikwenhere and Keswani, 1997).
Water lettuce or Nile Cabbage (Pistia stratiotes L.)
Origin: It has a cosmopolitan distribution throughout
tropical and sub-tropical regions. In South and Central
America, Africa and South-East Asia it is considered an
endogenous species.
Description: P. stratiotes is a perennial monocotyledonous
aquatic plant that floats on the water surface, with roots
hanging below floating leaves belonging to the family
Araceae.
Damage caused by the species: First observed in Mukuvisi
river in 1937, and 50 years later was the major aquatic
weed in northern Zimbabwe. By 1988, it had infested
Manyame river, Seke , Darwandale, Chivero, Kariba,
Chakoma, Chivake and Kaitano dams. Introduction of the
biological control weevil Neohydronomas affins in 1988
reduced infestations of the weed by more than 90% in all
the impoundments (Chikwenhere, 1994). No further
outbreaks of the weed have so far reported attesting to the
effectiveness of the biological control agent.
For more information contact Professor A. B. Mashingaidze.
[email protected] [email protected] mobile 0774999054
Azolla or Red Water Fern (Azolla filiculoides Lam)
Origin: According to Lumpkin and Plucknett (1980), A. filiculoides is
native to the Rocky Mountain states of the western USA and Canada,
through Central America and to most of South America. It has been
introduced to Europe, North and sub-Saharan Africa, China, Japan, New
Zealand, Australia, the Caribbean and Hawaii.
Description: A. filiculoides is a small aquatic heterosporous fern, rarely
larger than 25 mm (O'Keeffe, 1986). The genus is unique in that it
grows in association with a nitrogen-fixing heterocystous
cyanobacterium (blue-green alga), Anabaena azollae Strasburger
(Nostocales: Nostocaceae), which is located in cavities in the dorsal
leaf-lobes (Ashton and Walmsley, 1984).
Damage caused by the species: A. filiculoides spread to Zimbabwe in
about 1980 and now infests water bodies throughout the country. It
forms thick mats which eliminate submerged plants and algae, prevent
photosynthesis and oxygen diffusion from the air and anaerobiosis,
which eliminate fish and other animals from the water beneath them,
reducing biodiversity (Gratwicke and Marshall, 2001). In South Africa it
was effectively controlled through the release of a front feeding
Stenopelmus rufinasus Gyllenhal (Coleoptera: Curculionidae), that was
imported from Florida, USA (MaConnachie et al., 2003).