Aquatic Invasive Species

Scott Rong

Dr. Cooke

16 April 2010

News Dispatch on David Lung’s Research Pre-proposal regarding Giant Salvinia

Giant salvinia (Salvinia molesta), a free-floating aquatic fern, has origins from southern Brazil. However, this invasive fern has spread to many parts of Asia, the southern tropics of Africa, and now the United States. This fern is extremely difficult to manage due to its tenacity in a wide range of environmental variables and its reproductive success. The fern can survive in temperatures varying from 5C to 32 C and has been recorded to survive in severe winter temperatures as low as -3C and warm weather as high as 43C. This fern succeeds reproductively because it produces buds that break off from rhizomes, underwater roots. These buds flow with the water currents where they create new mats of giant salvinia. This characteristic allows giant salvinia to cover water surfaces rapidly. However, once the aquatic ferns cover entire water surfaces, low dissolved oxygen levels arise and kill native aquatic species. As a result, fish and birds migrate away from the body of water. Dead organisms decompose and lower the dissolved oxygen levels even further, causing less gas exchange between the water and the atmosphere. This leads to a sharp decline in photosynthetic phytoplankton until great salvinia completely blocks the sunlight from reaching the water. Today, only two methods of control are used against the giant salvinia: biological control in the form of the salvinia weevil (Cyrtobagous salviniae) and chemical control.

Mr. David Lung of Duke University hypothesizes that herbicides should act just as if not more effective than the salvinia weevil in restoring dissolved oxygen levels over a long period of time once control is achieved. And while native microorganisms will perish due to the herbicides, reintroducing microorganisms into the waters following herbicide treatment will accelerate the process of restoring dissolved oxygen levels.

Mr. Lung is an advocate of herbicidal use because while the salvinia weevil is a highly praised form of control, the weevil is not as resilient as the giant salvinia is to environmental conditions. For example, the salvinia weevil can survive only in temperatures ranging from 5C – 32 C, while the giant salvinia can survive in 16 C to 30 C temperature ranges. Therefore, organic compounds and a chemical approach is the most practical solution to controlling giant salvinia. While dissolved oxygen will decline after herbicides have been used, the restoration of microorganisms will greatly aid this process.

Mr. Lung will test his hypothesis in the Invasive Plant Research Lab in Fort Lauderdale, Florida. He will utilize three pond facilities overrun with giant salvinia. Each pond will have similar dissolved oxygen levels, mineral and nutrient content, and water temperature. One pond will serve as a control while the other two ponds will be tested with herbicides and salvinia weevil respectively. Dissolved oxygen levels after testing and possible microorganism restoration will be monitored for one year.

Mr. Lung hopes to find that the application of herbicides will replace the salvinia weevil as a main form of control. The reintroduction of phytoplankton into the waters after herbicidal treatment will restore dissolved oxygen levels to normal and will accelerate the water body’s recovery from the negative effects of giant salvinia.