Aquatic Invasive Species

By Emily Chang

A study proposed by Cameron Oswalt, who is an undergraduate student at Duke University, aims to find a method to control the Asian swamp eel (Monopterus albus) in the Florida Everglades. Ever since its introduction to the United States in the early 1990s from Southeast Asia, this aquatic invasive species is threatening the swamp ecosystems of Florida and other regions of the southwestern United States.

The Asian swamp eel has many characteristics that make it a difficult species to control. Although all eels are born as females, as adults they are able to change genders and reproduce during all times of the year. According to Oswalt, the eels are nocturnal and “can burrow underground if there is no water,” both of which make control of their populations even more difficult. In addition to these adaptations and characteristics, they can resist a variety of mechanical, physical, and chemical control methods. The Asian swamp eel can withstand poison treatment since they breathe air from the surface of their lake habitats; therefore, the poison in the water adversely affects native aquatic species instead. Other control methods, such as concussion-blasting and chemical pesticides, do not manage to reduce swamp eel populations.

Established as a National Park on May 30, 1934, the Everglades is an especially vulnerable region to be targeted by invasive species because of its great biodiversity. A variety of reptiles, mammals, birds, plants, and marine organisms live in this swamp environment, and out of all these species at least 60 are endangered. Scientists have attributed many instances of habitat destruction and species decline – especially of endangered organisms – to invasive species. Therefore, the Asian swamp eel can pose an enormous threat to the delicate, diverse environment of the Florida Everglades, and scientists should be concerned with the preservation of the biodiversity there.

Aware of the situation of the Everglades, Oswalt plans to use the reproductive adaptations of the Asian swamp eel to control the potential spread of this species to vulnerable environments, notably the Everglades. He intends to test the effectiveness of three control methods in four experimental ponds in Florida, one of which is the allocated control pond, and each will contain 50 adult swamp eels each. The three means of control tested in this experiment involve physical control, hormones, and poison. The physical control method will involve collecting the bubble nests laid by the eels for removal, and the hormone method intends to prevent swamp eel reproduction by using the hormone 17 alpha-methyltestosterone to change the eels into males. Oswalt predicts that both of these methods will be able to wipe out the Asian swamp eel populations in the allocated experimental ponds. However, the predicted results of the third control method involving poison are more uncertain. Oswalt believes that juvenile swamp eels can be more effectively controlled by poison than their adult counterparts because they have not yet developed all body parts fully and acquired the adaptations needed to resist control successfully. Because of this, he will use this third pond to test the ability of the juvenile swamp eels to withstand such a toxic environment. After three years of monthly monitoring and observation, Oswalt will examine both individual specimens and large samples. He hopes that the results of this experiment can help scientists apply and perhaps develop effective means of control on Asian swamp eels that can prevent ecosystem destruction in the Florida Everglades. Also, Oswalt believes that the information gained from this experiment may be applied to the control of other invasive species that are either exhibit “unprecedented” adaptations to control methods.