Ecological Risk Screening Summary - Giant Salvinia (Salvinia molesta) - High Risk

Species that are considered high risk have a well-documented history of invasiveness in at least one location globally and are of establishment concern for the contiguous United States based on a climate matching analysis.

Salvinia molesta, Giant Salvinia, is an aquatic fern that is native to South America. Depending on water conditions, S. molesta has been known to grow double its size in a matter of 2 to 6 days and can completely cover the surface of a slow-moving body of water with dense mats up to 1 meter thick. It is intolerant to salinity and ice. Giant Salvinia can be used as compost, fodder, crafting material, mulch, and for wastewater treatment and biogas generation. It is also present in the aquarium trade. Salvinia molesta has been listed as a Federal Noxious Weed since 1981 and is regulated in 24 U.S. states. Salvinia molesta has been introduced around the world, as well as to numerous states within the western and southern United States. It has established populations in many of those locations. S. molesta impacts submerged native plant species by altering water chemistry. Native benthic fish are affected as well by accumulated decomposed material and changes in water quality. Floating mats of S. molesta are known to impede waterflow, watercraft navigation, and is hazardous for people and livestock as it can be mistaken for solid ground. Economically, introduced populations impact commercial fishing, and recreational activities such as fishing, boating, and swimming. S. molesta can also clog pump intakes, irrigation, drainage canals, and block access to drinking water for humans, livestock, and wildlife. S. molesta is an important host for mosquitos known to be vectors of West Nile virus, St. Louis encephalitis, Venezuelan equine encephalitis, rural elephantiasis, malaria, and dengue fever. The History of Invasiveness for Salvinia molesta is classified as High due to these negative impacts of established populations. The climate matching analysis indicates establishment concern for this species. Areas of high match were mainly found in the Southeast and Southwest but most of the contiguous United States had a medium to medium-high match. The Certainty of Assessment for this ERSS is classified as High due to the high amount and quality of information available. The Overall Risk Assessment Category for Salvinia molesta in the contiguous United States is High.