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.

Journal of the World Aquaculture Society 2007; 38: 146-153

doi:     10.1111/j.1749-7345.2006.00083.x

The unique characteristics of the rice field eel (Monopterus albus), also known as the Asian swamp eel, have prompted scientists to examine the invading species in great detail hoping to better understand its lifestyle.  A team led by Qingsong Tan and Ruiguo He from Huazhong Agricultural University in China sought to determine the effects of different dietary supplements on swamp eel populations.

Their study focused on the effects of Vitamins A, C, D₃, and E.  Sixteen different dietary programs were prepared with varying levels of the vitamins in each, unique program.  The different diets were then fed to sixteen groups of yearling swamp eels for a total of forty-two days, and the effects of the different diets were recorded.  The recorded data focused on four areas: gonad production, lipid peroxidation, immunoglobulins, and calcium and phosphorous bone concentrations.  The results showed that Vitamin E benefited gonad development, vitamin C affected humoral responses, and Vitamins D and A aid in calcium absorption.

North American Journal of Fisheries Management 2006; 26: 949-952

doi:  10.1577/M06-023.1

The Asian swamp eel, which has already colonized four major locations in the southeastern US, has been labeled as a “major threat” to the nearby fragile ecosystems in the Everglades.  Methods to control or potentially eradicated the Asian swamp eel (Monopterus albus) are being pursued with little success.

One of the characteristics that has contributed to the eel’s widespread invasion is the species’ ability to obtain oxygen through surface air.  This trait rules out the option of using piscicides (fish poisons) to control the eel population.  However, a study conducted by Thomas Reinert and collaborators sought to determine if poison could be used to affect very young eels that still absorb oxygen through their skin.  Eels and control fish were exposed to different concentrations of Atimycin-A; however, the juvenile eels were unaffected, even at high concentrations.  Unfortunately, eradication through toxicants is probably not the answer to stopping the invasive eels, and other methods of biological control need to be studied.

The invasion of nonnative aquatic species is becoming one of the most threatening factors to freshwater and saltwater environments today.  The number of invasions and the wide diversity of both the types of invading species and the environments being invaded indicate that an effort must be made to halt the shocking rise in invasions of nonnative species.  Based on the readings and my research on the Asian swamp eel that is invading the Southeast, it appears that there are many similarities between the invasions of different species.  First of all, the methods of introduction of the nonnative species are typically the results of careless human contamination.  Whether it be ballast water, felt on the bottom of trout fishermen’s boots, or release of unwanted pets, the foreign invaders are introduced into new environments as the result of human interference with the environment.  Another similarity between most species involves the danger of their existence in their unnatural habitats.  Aquatic invasive species almost always affect the local populations, rather it be as competitors for food sources, invaders of habitats, or predators of other species’ juveniles.

I feel that if something is not done about aquatic invasions across the United States soon, the country’s ecosystems and wildlife will be in grave danger.  The interruptions that invading species can cause in food chains and environments could result in devastating ripple effects that affect all types of species.  The Asian swamp eel (Monopterus albus), which first appeared at the Chattahoochee Nature Center in Georgia, has spread rapidly throughout the Southeastern United States.  The biggest concern about the potential effects of the spread of the Asian swamp eel involves worry about advancement into the fragile ecosystems in the Everglades.  Not only is this species dangerous because it competes with native species for habitats, but it also competes with native species for feeding on small aquatic organisms as well as on the young of its competitors.  As is common throughout the realm of aquatic invasive species, the Asian swamp eel has a couple rare, but extremely beneficial, traits that promote its survival and propagation.  First of all, M. albus can move out of the water and slither across dry land as well as go for months without food, which are both clear advantages.  Asian swamp eels can also control their population and reproduction through a unique process.  All Asian swamp eels are born as females, and some change to males at maturation; however, the species retains the ability to change back into females if population declines.  The last, and most dangerous attribute of the Asian swamp eels, is that they are extremely difficult to eradicate.  They cannot be killed by explosion techniques because they lack the air bladders that make fish susceptible to concussion blasting, and they are also resistant to poisons that prevent fish from using oxygen in the water because the Asian swamp eels can just come out of the water and breathe air.

Given the difficulty to eliminate the aquatic invasive species that are already adapted to reproduce rapidly in certain environments, how can we prevent them from ruining ecosystems?  It is not humane to go to extreme measures and resort to ruthless killing, as was done to the mute swan population in the Chesapeake Bay area.  However, at the same time, it is in our best interest, as well as the planet’s best interest, to prevent these unnatural exposures from spiraling out of control and taking over stable ecosystems.  What steps must be taken, and what is going too far?  When it all boils down at the end, are the aquatic invasive species really doing anything wrong?  They are merely following Darwin’s theory of evolution, so why should humans interfere with a process of nature?

Cameron James Oswalt

References

http://www.anstaskforce.gov/Meetings/2009_November/Georgia%20Aquatic%20Nuisance%20Species%20Management%20Plan%20Sept%2009.pdf

http://anstaskforce.gov/ANSDigest-Feb01.pdf#page=5

http://www.anstaskforce.gov/spoc/swamp_eel.php

http://fl.biology.usgs.gov/Nonindigenous_Species/Swamp_eel_FAQs/swamp_eel_faqs.html