April 17, 2010

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.

Oxygen Needed

March 24, 2010

Oxygen Needed

By: David Lung

Giant salvinia is an invasive aquatic fern that quickly covers the water surface, outcompetes native aquatic plants, and kills other aquatic organisms due to a decrease of dissolved oxygen. Flores and Carlson (2006) worked with the salvinia weevil to figure out if there was a correlation between the control effects of the weevils on giant salvinia and also dissolved oxygen levels after the release of the weevils. Flores and Carlson (2006) reared the salvinia weevil in tanks with giant salvinia and released the weevils at 6 sites in Texas waterways. Insect population densities were sampled monthly to make sure that the insects were dispersing. Dissolved oxygen levels were then measured after a little over a year. Flores and Carlson (2006) observed a significant increase in dissolved oxygen levels following successful control. More research is needed to understand the relationship between the weevil and the fern in order to understand the difference in the amount of time needed for complete control.

Journal of Aquatic Plants Management. 44: 115-121

Guns and Roses

February 24, 2010


By: David Lung

Larson criticizes the militaristic language that biologists use in order to inform the public. Doing so would ultimately describe invasive species wrongly, cause a backlash from the people because we were at fault to begin with for bringing in these invasive species and create a fear of these plants that might be counterproductive to conservation. He argues that waging war is not a good description for controlling invasive species because they are a part of our lives now and we were the ones that gave them the opportunity to live in foreign environments. Also, he states that it is impossible to completely get rid of these species from ecosystems they have already invaded and the methods to restore a particular ecosystem might cause further problems. Larson states that the rhetoric should be toned down considerably and we should work on preventing the spread of invasive species and accept that they are a part of the ecosystems they now inhabit based on our own actions

“Cyrtobagous Salviniae destroyed terminal and lateral buds on the parent plant which partially compensated for this loss by producing new buds of higher order rank, some of which were also attacked by adults and larvae.” (Forno and Semple 1987)

I saw this quote on a study of the salvinia weevil as a potential biocontrol agent of giant salvinia (salvinia molesta). Using terms like “destroyed” and “attacked” gave this sentence a militaristic tone. The authors could have stated that the salvinia weevil ate the terminal and lateral buds or simply that the insect controlled the giant salvinia by doing so. I somewhat disagree with Larson’s argument though. In my opinion it is obvious that we were the main agents that brought invasive species, but to allow these invasive species to live with us when they already do so much damage to the ecological services native organisms provide, it does not make sense to live peacefully with them. The damage these invasive species do is not overexaggerated for the most part. They are essentially parasites, outcompeting native species that have already reached an equilibrium with their ecosystem and also disrupting the overall balance of the ecosystems they now inhabit. The backlash he talks is somewhat probably because these invasive species such as the Sitka black-tailed deer that help people with a lower socioeconomic status. Overall, I do believe the militaristic tone is necessary and effective for preserving what is left of pristine ecosystems from invasive species, but also to restore invaded ecosystems to the best of our ability because we are at fault for disrupting those ecosystems and should be reminded in the urgency of the problem we’re responsible for.


Larson, B.M.H. 2005. “The war of the roses: demilitarizing invasion biology.” Frontiers in Ecology and the Environment 3: 495-500.

Forno, I.W. and J.L. Semple. 1987. “Response to Salvinia Molesta to insect damage: changes in nitrogen, phosphorus, and potassium content.” Oecologia. 73: 71-74.

Weevil Wonder

February 6, 2010

Journal of Aquatic Plant Management 44: 115-121 (2006)

Giant salvinia (Salvinia molesta) is a noxious aquatic fern native to Southern Brazil that has threatened many freshwater ecosystems. Giant salvinia reproduces rapidly by fragmenting part of their stems to create a new plant. Its overgrowing has replaced native vegetation, altering the food web of the aquatic ecosystems, and also reduced dissolved oxygen levels, which eventually asphyxiates all aquatic life. It hinders irrigation, clogs waterways and promotes diseases in the stagnant waters the fern creates.

Daniel Flores and J.W. Carlson of the USDA introduced the salvinia weevil (Cyrtobagous salviniae) to control the fern. Herbicides usually exacerbate the situation or are not effective. The places where the researchers introduced the weevils have a significant decrease of the fern and an increase in dissolved oxygen levels. The giant salvinia population has remained constant and the weevils have shown to only consume the fern and nothing else. The authors say more research is needed, but biocontrol has shown to be an effective option.