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   Salvinia molesta (aquatic plant, herb) français     
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         General Impact

    Salvinia molesta can form dense vegetation mats that reduces water-flow and lowers light and oxygen levels in the water. This stagnant dark environment negatively affects the biodiversity and abundance of freshwater species, including fish and submerged aquatic plants. S. molesta can alter wetland ecosystems and cause wetland habitat loss. Salvinia invasion also poses a severe threat to socio-economic activities that are dependent on open, flowing and/or high quality waterbodies, including hydro-electricity generation, fishing and boat transport.
    For more details on the general impacts of this species please see general impacts of Salvinia molesta

         Location Specific Impacts:
    Australia English 
    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.

    Economic/Livelihoods: The weed has had a devastating socioeconomic impact in parts of Australia (McFarland et al., 2003).
    Northern Territory (Australia) English 
    Habitat alteration: In the Northern Territory of Australia the flood plain habitat of the 'Least Conern (LC)' Yellow-billed Egret (see Mesophoyx intermedia) is degraded due to grazing, burning, invasion by introduced plants (particularly Mimosa pigra and Salvinia molesta, reduced water flows from drainage and water diversion for irrigation, levee breaking by feral buffalo (Bubalus bubalis) etc. (BirdLife International 2012)
    Kakadu National Park (Australia) English 
    Habitat alteration: Salvinia 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 (Agriculture & Resource Management Council of Australia & New Zealand, Australian & New Zealand Environment & Conservation Council and Forestry Ministers, 2000). Salvinia and other weed species like Mimosa, as well as feral pigs present an ongoing threat to the wetland habitat in the Magela Creek System (Gardner and Finlayson, 2002).
    South India (India) English 
    Agricultural: In India salvinia is a serious weed in ricelands (McFarland et al., 2003).
    Borneo (Indonesia) English 
    Economic/Livelihoods: 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.
    Lake Naivasha (Kenya) English 
    Economic/Livelihoods: The floating water fern Salvinia molesta has occurred in Lake Naivasha since the early 1960s and during this period has obstructed fishing activities and navigation.

    Human nuisance: The floating water fern Salvinia molesta has occurred in Lake Naivasha since the early 1960s and during this period has obstructed fishing activities and navigation.

    Threat to endangered species: Salvinia infestations reduce the quality of the wetland habitat of the 'Near Threatened (NR)' Maccoa duck (see Oxyura maccoa in the IUCN Red List of Threatened Species) (Berrutti et al 2007)
    Papua New Guinea English 
    Disease transmission: Salvinia molesta mats provide an ideal breeding ground for mosquitoes, which are known disease vectors for malaria in Papua New Guinea.

    Economic/Livelihoods: 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 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). 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.
    Philippines English 
    Economic/Livelihoods: The weed has had a devastating socioeconomic impact in parts of the Philippines (McFarland et al., 2003).
    Senegal English 
    Economic/Livelihoods: 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.

    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).
    South Africa English 
    Disease transmission: By altering the habitat salvinia increases the level of mosquitoes and disease in the aquatic environments where it occurs in (Bromilow, 1995, in Van Wilgen et al, 2001).

    Habitat alteration: In South Africa salvinia degrades aquatic ecosystems and alters the flow of rivers (Bromilow, 1995, in Van Wilgen et al, 2001).
    Sri Lanka English 
    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 2 ha to 25 ha) 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. molestaE. crassipes) pose a serious threat to irrigation systems such as these.
    Annaiwilundawa Tanks Sanctuary (Sri Lanka) English 
    Reduction in native biodiversity: The effects of alien invasive water plants (Eichhornia crassipes, S. molesta, Imperata cylindrica and Mikania micrantha) on the pheasant-tailed jacana (see Hydrophasianus chirugus in the IUCN Red List of Threatened Species) was studied in three reservoirs from June 2004 to May 2005 at the Annaiwilundawa Ramsar site of northwestern Sri Lanka. Jacanas were observed in significantly fewer numbers among invasive plants and open water and in significantly higher numbers among grass and floating leaved plants. The findings of this study revealed that the most critical factor for the occupation of the reservoirs by jacanas was the water level and that the spread of the invasive plants in these reservoirs were detrimental to jacanas, since these plants deprived jacanas of useful foraging habitats (Mahaulpatha et al 2008).
    Hawaii (United States (USA)) English 
    Threat to endangered species: Salvinia molesta in Enchanted Lake (Kailua) threatens the habitat of three endangered waterbird species, the 'Vulnerable (VU) Hawaiian coot (see Fulica alai), the Hawaiian common moorhen (Gallinula chloropus sandivicensis) and the Hawaiian stilt (see Himantopus mexicanus knudseni)-both of which are listed as Endangered by the US Fish and Wildlife Service.
    Texas (United States (USA)) English 
    Agricultural: In Borneo salvinia is a serious weed in ricelands.

    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.
    Zimbabwe English 
    Agricultural: More than 40 plant species have colonised S. 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).

    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).

    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.
    Tengwe Tobacco Commercial Farming area (Zimbabwe) English 
    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).

ISSG Landcare Research NBII IUCN University of Auckland