Salvinia molesta (aquatic plant, herb)

Ecology Distribution Management Info Impact Info References and Links Contacts

General Impact For details on impacts of this species please see general impacts          Location Specific Impacts: Senegal River (Africa)   Ecosystem change: The original floodplain ecosystem of the Lower Senegal River Delta is preserved in two national parks by artificial water flow regulators: the Djoudj National Park (also known as the Djoudj National Bird Sanctuary) in Senegal and Diawling National Park in Mauritania. These are important areas for tropical and Palearctic birds. The invasion of the Senegal River by S. molesta posed a significant threat to the biodiversity of the ecosystems preserved in these areas (IUCN, 2002; Hamerlynck, Baba and Duvail, 1999; Anon, 1995, in Pieterse et al, 2003). Human nuisance: The weed blocked the inlets of national parks, irrigation channels and the open corridors through the Typha fields (that were cleared by locals). Attempts by the local people to remove S. molesta from fishing areas and irrigation channels failed. Along with other invasive aquatic plants the weed contributed to the isolation of villages (and villagers) from open water bodies. Argentina   Human nuisance: Although native to this region, the weed has the potential to aggrevate problems related to navigation and water flow in irrigation canals. Australia   Disease transmission: Salvinia molesta mats provide an ideal breeding ground for mosquitoes, which are known disease vectors for Ross River virus and viral encephalitis in Australia (anon, 1997, in ARMCANZ, 2000) Economic/Livelihoods: The weed has had a devastating socioeconomic impact in parts of Australia (McFarland et al 2003). Northern Territory (Australia)   Habitat alteration: The yellow-billed Egret (Mesophoyx intermedia) is listed as Least Concern (LC) in the IUCN Red List of Threatened Species. Its habitat in the Northern Territory of Australia is under threat due to burning, grazing and the spread of invasive alien plants Mimosa pigra and Salvinia molesta. The introduced feral buffalo Bubalus bubalis is also a threat causing breakes in the levees leading to salt intrusion and accumulation of salt settlement (BirdLife International 2009). Kakadu National Park (Australia)   Habitat alteration: S. molesta reduces oxygen diffusion into the water reducing the quality of the habitat for fauna and encouraging animals to search for better conditions if possible. In Kakadu National Park bird species that used open water were excluded from areas of water heavily infested with S. molesta. Small fish and file snake numbers were also reduced (Storrs and Julien, 1995, in ARMCANZ, 2000). Other: Weed species such as salvinia and mimosa, as well as feral pigs present an ongoing threat to the wetland habitat in the Magela Creek System (Gardner and Finlayson, 2002). Southeastern Brazil (Brazil)   Human nuisance: Although native to this region, the weed has the potential to aggrevate problems related to navigation and water flow in irrigation canals. South India (India)   Agricultural: In India salvinia is a serious weed in ricelands (McFarland et al., 2003). Borneo (Indonesia)   Agricultural: In Borneo salvinia is a serious weed in ricelands. Kenya   Economic/Livelihoods: Salvinia mats and their harmful affect on aquatic fauna (including fish) had serious consequences for fisheries based on Lake Naivasha. Human nuisance: Lake transport on Lake Naivasha was hindered by the think mats formed by salvinia Other: Salvinia threatened wetland fauna and flora in Lake Naivasha. Papua New Guinea   Disease transmission: S. molesta mats provide an ideal breeding ground for mosquitoes, which are known disease vectors for malaria in Papua New Guinea (anon, 1997, in ARMCANZ, 2000). Economic/Livelihoods: In parts of Papua New Guinea heavy salvinia infestations have caused a reduction in fish numbers and have made it difficult to use seine, gill and cast nets and long lies. Other: Near the Sepik river entire villages had to be abandoned because they were entirely dependent on water transport. When the lakes and lagoons beside villages became chocked with salvinia and water hyacinth (E. crassipes) villagers could no longer travel to trade, fish or harvest staple foods. Access to schools and hospital care was also blocked (Howard and Harley, 1998; Mitchell et al., 1980, Thomas and Room, 1986a, in McFarland et al., 2003). Philippines   Economic/Livelihoods: The weed has had a devastating socioeconomic impact in parts of the Philippines (McFarland et al., 2003). Senegal   Ecosystem change: The original floodplain ecosystem of the Lower Senegal River Delta is preserved in two national parks by artificial water flow regulators: the Djoudj National Park (also known as the Djoudj National Bird Sanctuary) in Senegal and Diawling National Park in Mauritania. These are important areas for tropical and Palearctic birds. The invasion of the Senegal River by S. molesta posed a significant threat to the biodiversity of the ecosystems preserved in these areas (IUCN, 2002; Hamerlynck, Baba and Duvail, 1999; Anon, 1995, in Pieterse et al, 2003). Human nuisance: The weed blocked the inlets of national parks, irrigation channels and the open corridors through the Typha fields (that were cleared by locals). Attempts by the local people to remove S. molesta from fishing areas and irrigation channels failed. Along with other invasive aquatic plants the weed contributed to the isolation of villages (and villagers) from open water bodies. South Africa   Disease transmission: By altering the habitat salvinia increases the level of mosquitoes and disease in the aquatic environments where it occurs. Habitat alteration: In South Africa salvinia degrades aquatic ecosystems and alters the flow of rivers. Sri Lanka   Agricultural: In Sri Lanka salvinia is a serious weed in ricelands (McFarland et al., 2003). Disease transmission: Mats of salvinia provide ideal habitat for Mansonia mosquitoes, a principal vector of rural elephantiasis in Sri Lanka (Pancho and Soerjani, 1978, in Julien, Center and Tipping, 2002). Economic/Livelihoods: In Sri Lanka there are some 50,000 reservoirs (ranging in size from 2ha to 25ha) which have been constructed over the past 3000 years (mainly for irrigating rice fields). During the early 1980s 25% of the rreservoirs were infested with S. molesta. An investment of US$4 billion has been placed in constructing dams, irrigation systems and hydropower generators along the Mahaweli Ganga (the largest river in Sri Lanka), which carries water from the central mountains to the northeast coast. Alien invasive aquatic plants, including S. molesta and water hyacinth (E. crassipes) pose a serious threat to irrigation systems such as these. Hawaii (United States (USA))   Other: S. molesta in Enchanted Lake (Kailua) threatened the habitat of three endangered waterbird species, the Hawaiian coot (see Fulica alai in IUCN Red List of Threatened Species), the Hawaiian gallinule (Gallinula chloropus sandivicensis) and the Hawaiian stilt (Himantopus mexicanus knudseni). Texas (United States (USA))   Agricultural: Salvinia may clog water intakes to hydro-electric stations or interfere with agricultural irrigation. In many farm ponds in Texas it blocks creeks that drain into tributaries that are heavily used for agricultural irrigation. Human nuisance: In Texas (in the Swinney Marsh Complex) local fishermen have found it impossible to cast fishing nets and lines into the water due to the dense expansive S. molesta vegetation. As a result some spots once fished for bass, crappie and sunfish, have to be abandoned. Zimbabwe   Agricultural: More than 40 plant species have colonised Salvinia molesta mats on Lake Kariba. These deceptive floating islands of vegetation entice grazing livestock and have caused a number of deaths due to the animal breaking the mat and becoming stuck (Boughey, 1963, Harper, 1986, in McFarland et al., 2003). Disease transmission: In Lake Kariba the dense salvinia mats have fostered the build up and spread of Biomaphalaria boissyi, a snail that is the intermediate vector of bilharzia (schistosomiasis) (Bennett 1975, in McFarland et al., 2003). Economic/Livelihoods: Salvinia has negatively affected agriculture, farming and fisheries by disrupting irrigation systems, blocking access to drinking holes and lowering oxygen levels in the water (which harms aquatic fauna). Tengwe Tobacco Commercial Farming area (Zimbabwe)   Economic/Livelihoods: Since this area is a commercial farming area, salvinia infestations were particularly harmful to economic sectors. The thick salvinia mats growing on the water surface prevented livestock from being able to access and drink from the dams. Salvinia disrupted agricultural irrigation systems (by blocking irrigation channels) which resulted in a reduction in crop productivity. Due to the reduction of oxygen dissolved in the water (and other ecophysiological changes associated with dense aquatic plant mats) salvinia harmed the fish stocked in the dam.