Transcript AQUATIC INVASIVE SPECIES IN ZIMBABWE

Chinhoyi University of Technology
Invasive Species Research and Management Unit
EMERGING (NEW) AQUATIC INVASIVE SPECIES IN ZIMBABWE
Parrot’s feather (Myriophyllum aquaticum (Vell.) Verdc.)
Origin: Native to the Amazon River in South America
Description: A perennial plant that gets its name from its feather
like leaves that are arranged around the stem in whorls of four to
six. Stems and leaves are submerged in the water but also
emerge above the water and can grow more than 30cm above
the water looking like small fir trees. The woody emergent
plants extend to the bank and shore and can grow 1.5m tall. Only
female plants exist outside its native range and it does not
reproduce sexually as an alien invasive species. It establishes from
stem segments, asexually. Stem apices are better than other plant
parts as vegetative propagules, therefore during mechanical
control there is need to limit the number of loose stem apices
produced and they should not be allowed to drift down stream
where they can start new infestations of the weed.
Damage caused by the species: The aquatic plant can cover large
areas of lakes and ponds especially towards the shore and impede
access and navigation to fishing, recreational and tourism
facilities. In Lake Chivero, water hyacinth covered 35% of the Lake
surface, (36.6%) and Parrot’s feather covered only 1.7% in 1985.
Ten years later in 1995, the estimated weed coverage was water
hyacinth 3%, P. stratiotes 0.3%, Parrot’s feather (4%) and Azolla
filiculoides (1%). In 2000, weed coverage was water hyacinth
2.4%, P. stratiotes 0.8%, Parrot’s feather 6.8% and Azolla
filiculoides 3.5% (Chikwenhere, 2001). The emergence of Parrot’s
feather as a major invasive aquatic weed species in Lake Chivero
is a result of a combination of lack of natural enemies and
competition from dwindling populations of water hyacinth and
through chemical, mechanical and biological control and P.
stratiotes as a result of biological control (Chikwenhere, 2001).
Integrated management of all species is recommended to prevent
new species occupying the ecological space created by the
effective control of one or more species in the Lake.
For more information contact Professor A. B.
Mashingaidze. Invasive Species Research and Management
Unit, [email protected] [email protected]
mobile 0774999054
Spaghetti Weed/ Pennywort (Hydrocotyle ranunculoides)
Origin: Native to North and South America and parts of Africa
Description: Spaghetti weed belongs to the family Apiaceae (the carrot
family). It spreads through vegetative extension of rhizomes that root at
nodes and by seed. The rhizomes float in water. Leaves grow on petioles
up to 35 cm long and are round to kidney shaped with 3-7 lobes. Flowers
are small, white to pale yellow and fruits are small achenes than can
float, helping in dispersion of the seed.
Damage caused by the species: In Manyame riverine system and Lake
Chivero in 1985, the water was covered by the following aquatic weeds;
water hyacinth (35%), Pistia stratiotes(36.6%) and Myriophyllumm
aquaticum (1.7%). By the year 2000, as a result of mechanical, chemical
and biological of water hyacinth and biological control of water lettuce
(Pistia stratiotes), Spaghetti weed (Hydrocotyle ranunculoides) invaded
Lake Chivero and covered 9.5% of its surface ( Chikwenhere, 2001).
Flowers form umbrella
like clusters (umbels)
and fruits are dehiscent
achenes the float in
water. The seeds
germinate in sediments
on the shores of the
river or lake and small
seedlings detach from
the sediments and float
in the water
Like all other aquatic weed species, spaghetti weed forms thick mats
that impede navigation of the lake and river by boat for recreational
and commercial purposes. Access to fishing and other tourism facilities
is denied. The weed changes the aquatic habitat by using up oxygen in
the water and decomposing mats of the weed may further
deoxygenate the water and cause fish kills. The weed slows down
water movement in irrigation canals and blockages of canals may cause
flooding. The weed has potential to causes massive losses in water
from reservoirs through transpiration . The ability of the weed to slow
down water currents increases breeding habitat for the malaria causing
anopheles mosquito. Other disease vectors such as Mansonioides
mosquitoes, the vectors of human lymphatic filariasis causing
nematode Brugia, can breed on this weed.
For more information contact Professor A. B. Mashingaidze.
Invasive Species Research and Management Unit,
[email protected] [email protected] mobile
0774999054