Aquatic Invasive Species

Ballast water, water used by ships for stabilization, is a known vector for the transport of foreign species from port to port. It is estimated that as many as 10,000 different species are transported daily, including invaders that could and have caused millions of dollars of economic damage and untold environmental impacts on the ecosystems to which they have been introduced. Many methods have been suggested and used for the control of ballast water, both mechanical and chemical. These include ballast water exchange, where water from the harbor is let out in exchange for water from the open ocean, and various methods that can be used on board the ships, including biocides, filtration, and thermal and chemical treatments. However, each of these approaches has different strengths and weaknesses.

Tara Porter of Duke University has suggested a way to identify ballast water organisms on board moving ships. To do this, she suggests testing first the ability of DNA microarray systems to identify different organisms in lab by setting up tanks with similar environments to those found in the ballast areas of ships. Porter’s study will then introduce different known invasive species to the tank, which will next be tested using DNA microarrays. The results from this analysis will then be compared to the species actually introduced to the tanks to see which species the technique was able to detect. To test this method on board, Porter then plans to partner with a shipping company to use the technique aboard their ships.

Porter hopes to find a way to determine the types of invasive species on board without having to send samples off ship for testing. This is at present not possible, and will prove a major enhancement in monitoring invasive species and preventing their spread through shipping. Furthermore, the results of the study could be used to analyze the efficacy of current treatments, and help find the most effective technique  for the on board treatment of ballast water and the prevention of the spread of 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.

The red lionfish (Pterois volitans), popular among many aquarium enthusiasts, is a large fish native to the indo-Pacific region of the Pacific ocean. It has few predators and is able to survive in a variety of conditions, making it a formidable invasive species. Originally introduced into the Atlantic Ocean along the coast of North America, it has since damaged Bahamian ecosystems and reef systems.

Red lionfish populations in the Bahamas have been observed to be at a density of 390 lionfish/hectare, a density high than recorded even in their native habitats. Its high rate of population growth is due to a lack of any predatory fish in the Atlantic Ocean. A lack of competition has enabled these invaders to decrease Atlantic fish recruitment in the Bahamas to coral reefs by 79%.

Rui Dai of Duke University, among numerous other researchers, postulates that not all hope is lost for the Bahamian coral reefs. In 2008, several Nassau and tiger grouper (native Bahamian grouper species) were found to have lionfish remains in their stomachs. Dai is interested in whether these Bahamian grouper, perhaps with the help of humans, may be able to serve as natural biocontrol for the red lionfish.

To test her theory, Dai plans to place several groups of different proportions of the grouper, the lionfish, and other fish species native to the Bahamas in commercial fish pens, which are used while still in the ocean. This type of fish pen will be used because it should enable salinity levels, etc., in the experiment to be identical to those in the Bahamas, the environment in which the results of this study are applicable.

Each test group will contain one Bahamian grouper (of either species) and two, four, or eight lionfish, as well as a variety of crustaceans, small fish, and squid found in the Bahamas. Dai will also test the grouper at different ages (five months old, one year old, and five years old) to see whether only the largest adult grouper could be successful biocontrol agents. Each morning, Dai plans to observe which species are still present in each pen. The entire study will last approximately three months, after which point Dai expects to have enough data to draw conclusions about the approximate success of Bahamian groupers as biocontrol agents against red lionfish.

Dai expects that large numbers of the adult grouper will be the most successful biocontrol agents, though human assistance will be imperative for their success. Once Dai has obtained results from her study, she hopes that others will continue research about how to best implement Bahamian grouper as biocontrol agents against the red lionfish.

Since being introduced to Australia to combat sugar cane crop destruction caused by the Frenchi cane beetle, the cane toad (Bufo marinus) has wreaked havoc on both native organisms and Australian ecosystems as a whole. Cane toads pose a particularly severe ecological threat due to their virtually limitless diets and poisonous qualities; they readily consume nearly anything in sight and release toxins that can eliminate most of their predators. However, previous research has shown that one of its predators, the meat ant (Iridomyrmex purpureius), can consume cane toads without being afflicted by its toxins.

In the past, researchers have implemented various methods in an effort to control cane toad populations, including certain forms of biocontrol. Unfortunately, their efforts have generally been met with limited success.

However, recent research has been revealed that may help lead to the development of a more effective method of preventing cane toad invasion. Scientists have discovered that cane toads primarily rely on their sense of smell when seeking out prey. This information may be a key component in a novel, innovative control method that utilizes certain odors to which both the cane toad and its predators are attracted.

Duke undergraduate Chris Rzeznik and his team are attempting to further develop this approach in an experiment that exploits both the cane toad’s vulnerability to meat ant consumption and its attraction to the scent of cat food. Building on the knowledge that both cane toads and meat ants have proven to be attracted to cat food, Rzeznik and his team have devised a procedure to lure both species together using their shared food preferences.

The researchers aim to assess how the cane toad’s sense of smell can be used to control its spread by identifying the foods to which both cane toad. To accomplish this, they will replicate the Australian environment in six simulated habitats, four of which will contain cane toads and two of which will contain meat ants. One will contain both species in order to examine the extent to which the ants will prey on the toads when adequately exposed to them. The corners of each habitat will emit the scent of cat food, and the researchers will record activity at each corner for one week to determine the level of attraction that both species exhibit to the odor.

The researchers speculate that if they are successful in using shared food preferences to lure these species together, they can deduce that small rodents and insects will be the most reliable bait in doing so in future studies. If their experiment ultimately produces no conclusive outcome, the researchers plan to retry it with modifications of certain variables, such as the use of insects like the lavender beetle (Cydnidae) as bait instead of cat food.

Although their study may have various motives, the researchers’ main concern is the welfare of the Australian environment. According to Rzeznik, “the overarching effect our team hopes to have is that by stopping the cane toad invasion, we will restore the uniqueness of Australia’s wildlife and rid this country of a pest that has caused problems for decades.”

The Red lionfish – a colorful, yet poisonous tropical fish – is native to the coral reefs of the southeastern Pacific. In 1992, a hurricane damaged a Florida aquarium, and Red lionfish were released into the wild. Since then, the lionfish has spread up the Atlantic coast. Their invasion poses an ecological problem because they have very few predators, due to their dangerous venom. Researchers are unsure of the threat that this fish poses to biodiversity in its new habitat.

Traditional bio-control methods offer limited hope for containing the lionfish population because of the lionfish’s lack of predators and wide distribution throughout the Atlantic Ocean, says Frank Chang of Duke University. He is proposing a study of the lionfish’s food sources, to see how different food sources affect the growth rate of the fish. He plans to send research teams to multiple locations across the Atlantic coast, where they will monitor, catch, and analyze the stomach contents of lionfish.

The results of the study will help to elucidate why lionfish have higher growth rates in some areas, and lower growth rates in others, if they are caused by specific local lionfish diets. Chang hopes that this work will help biologists to develop a “ranking system” of areas where Red lionfish have invaded, so that control efforts can be better directed to areas that may be at higher risk of lionfish colonization.

DURHAM, NC — The killer shrimp (Dikerogammarus villosus) is one of many species worldwide that has expanded beyond its native habitat and become known as an aquatic nuisance species.  Originally found only in central-eastern Europe, it has invaded waterways throughout the continent, where it attacks and eliminates native gammarid species.  With large, powerful mandibles, the killer shrimp is capable of consuming a variety of prey and outcompeting other amphipods.  It gets its name from its destructive behavior, killing far more prey than it can eat, and has even been known to attack small fish.  Within a short time after invading a new area, it can eliminate a wide range of species from the ecosystem, drastically altering the interactions of the food web.

At present, there have been no reports of killer shrimp in North America.  However, the transportation of this destructive invader to the U.S. is not out of the question, as everyday thousands of gallons of foreign water are brought into the country through the ballast water of ships.  This is one of the most common means by which species are transferred between continents, and has been responsible for countless aquatic invasions in the past.

In hopes of preventing the establishment of a killer shrimp population in the U.S., Bernard Jiang of Duke University has proposed a study to test the effectiveness of ballast water treatment on killer shrimp.  Jiang’s study will examine the four main types of ballast water treatment: mid-ocean ballast water exchange, biocides, heat treatment, and filtration, in an attempt to determine which is best suited to eliminating the shrimp from a ship.  Jiang intends to use tanks of water to simulate a ship’s ballast container, controlling temperature, salinity, oxygen level, and all other abiotic factors.  The researchers will put live shrimp specimens at every stage of life into the tanks, perform one of the treatment methods on each tank, and record the number of live shrimp still in each of the tanks after treatment.

The goal of this study, according to Jiang, is “to determine which ballast water treatment is most effective at controlling the shrimp”.  This in turn, he elaborates, “will help prevent the spread of killer shrimp, and will also provide insight into the effectiveness of treatment methods in general”.  There have been previous experiments testing the relative effectiveness of different methods of ballast water treatment, but this would be the first study to focus specifically on killer shrimp.  As such, it would provide species-specific results that would suggest the best way to prevent the introduction of the shrimp into the U.S., explains Jiang, as well as contributing to the general body of knowledge regarding ballast water treatment as a whole.

According to the researchers, killer shrimp should be one of the main priorities targeted by invasive species policy creators, as it could “cause unprecedented amounts of damage” if introduced, yet there is still the possibility of preventing it from doing so.  “Killer shrimp have only appeared on the invasive species radar in the last decade,” says Jiang, “but they have been particularly effective in their invasiveness.”  For this reason, he argues, it is essential that research be done immediately to determine how best to keep the shrimp out of North America, while there is still the chance to do so.

The Chinese mitten crab (Eriocheir sinensis) is native to rivers and estuaries on the east coast of Asia, and is considered a delicacy in its Asian homeland. Chinese citizens will pay hundreds of Yuan to taste even a small crab from the Yangcheng lake, as this crustacean is supposed to have a cooling (yin) effect on the body. In other parts of the world, however, what the Chinese mitten crab has been up to is anything but cool. IN the early 1900’s, isolated populations of this species began to appear in northern European countries such as Germany. The Chinese mitten crab has made its way to America through several vectors such as ballast water and unintentional releases, and the area experiencing the most rapid crab invasion is the San Francisco Bay Area.

It’s no secret why these crabs are considered an invasive species when it comes to outlasting their environment. Unlike most freshwater crustaceans, Chinese mitten crabs can survive in marine and even polluted waters, and tolerate uptake of heavy metals, such as Cadmium, for several days. They also have the ability to cross natural barriers such as rapids or dams. Chinese mitten crabs also have a variety of detrimental effects on their environment. E.sinensis is very aggressive, and often outcompetes native crayfish and crab species for resources like space and shelter, as well as food sources.

Mitten crabs often clog pumps, screens, and intakes, and they continue to get caught in shrimping nets, costing the shrimping industry a lot of time and money. Sediment loss and erosion has been shown as an effect from the burrowing of Chinese mitten crab, causing damage to stream banks and levees. Several methods of control have been tried, such as placing traps upstream to catch young crabs during migration, but none have successfully been able to reduce the Chinese mitten crab invasion. The damage that these crabs have caused to the environment is what has led researcher Emilia Rybak to further investigate what can be done.

Modeling their experiment after research done by Cecily C. Natunewicz, Charles E. Epifanio, and Richard W. Garvine, Rybak and her team of researchers aim to see if they can track larval trajectories, or the small migratory pathways of the patches of eggs. This will allow them to see what environmental factors are most responsible for the dispersal of larval patches, and if there is any hope of being able to control the Chinese mitten crabs from their egg stages. Rybak and her team intend to tag separate larval patches in the San Francisco Bay with satellite-tracked drifters attached to buoys at the surface. While doing this, they will be keeping track of physical conditions such as salinity, temperature, and river discharge. This should allow them to simulate general patterns of larval transport and will be helpful in assessing the correlation between the small scale movement patterns and the general trajectories of larval patches.

Rybak and her team all acknowledge the dangers of letting the Chinese mitten crab populations go unchecked in the United States, particularly the San Francisco Bay area. She hopes that her research will shed light on the migratory pathways of Chinese mitten crab larval patches. This will hopefully, in turn, allow for the development of more effective management techniques and the prevention of population growth by targeting the problem in its earliest stages.

Durham, N.C. – The common reed (Phragmites australis) is an invasive plant from Europe. This species was not known to have existed in the United States because there is a similar genotype of Phragmites that is native to North America. The plant grows at a rapid growth rate and due to its large networks of underground growth that siphon nitrogen, which makes it difficult for other plants to reside in the habitat.

The European Phragmites has spread throughout the wetlands of North America, especially the Chesapeake Bay region. Even though both the native and the European reed have the same phenotype, Mason Reynolds states that “the native Phragmites has been completely out competed by European phragmites and is assumed not found in Chesapeake Bay wetlands.”

The European Phragmites that now dominates most of the North American wetlands causes detrimental effects to many plants and animals. They displace native plant communities, such as the native Phragmites and the marsh cordgrass (Spartina alterniflora). The dense biomass of the European Phragmites also alters the marsh topography, changes the chemistry of the soil, and cycles nutrients differently. This causes extensive damage to the ecology and the economy. For example, the change in the topography reduces the amount of habitat that the blue crab (Callinectes sapidus) can survive in by reducing the number of sheltering pockets for the young crabs to live in until their adult stage. Therefore, this damages the blue crab fishing industry in the Chesapeake Bay region, reducing the monetary gain from fishing.

Recent efforts in determining the establishment were very limited. Reynolds states that this was because most of the studies were done in the 1990’s, when GPS and satellite technology were not advanced. These studies usually had a survey size in the 2000’s in seven wetlands throughout a survey site. This survey size is said to be too small in sized and therefore, does not give any significant trend in the spread of Phragmites. Therefore, a more extensive survey was needed in order to determine the spread and quantity of the reed.

Reynolds and her team of researchers are proposing to analyze the invasion of Phragmites by investigating the role of human activity in order to determine strategies for managing and possibly eradicating the invasive plant. In order to do so, she will evaluate the abundance of Phragmites in the coastal wetlands and determine if the abundance is due to human development.

To do this, a minimum of 90, one hectare survey sites will be chosen at random following two parameters: there will be an equal number of sites chosen at each shoreline and they will be evenly distributed. Development near the sites will be categorized as urban, suburban, or agricultural. These sites will be determined if the area next to the borders of the survey site are “developed” or “undeveloped.”

Ariel photographs will then be taken to see where Phragmites is abundant. They will stand out from the environment due to their grey texture. GPS systems will then be used to triangulate the boundaries of Phragmites. This data will be compared with other survey sites to see the abundance and the type of development near the survey site.

Reynolds hopes that this study will determine the distribution and abundance of Phragmites throughout the Chesapeake Bay wetlands. Since total eradication is improbable, she hopes that this new survey will better show the abundance and how development contributes to the growth of Phragmites, which will make it easier to allocate management resources towards prevention and management of this invasive plant.

The European green crab (Carcinus maenas) poses a devastating problem to the ecosystem and fish economy on both the east and west coasts of the United States. It out-competes many local crab species for food resources, and as a result, reduces the local shellfish population that is crucial for the economy and ecosystem. There are currently many speculations of how the European green crab can be contained, but none of which have been empirically proven to be effective.

Jenna Barbee of Duke University proposes using Sacculina carcini, a parasitic barnacle, to control the green crab population. S. carcini prevents the green crab from developing reproductive organs, and ultimately kills the host organism. The parasite has been demonstrated to be relatively host-specific, in that it only targets a specific set of species of crab, which allows it to be a potential viable bio-control. However, there is little systematic research concerning whether the parasite attacks native US crab species. Barbee’s proposed project therefore targets the question of whether S. carcini is a feasible bio-control option for the invasion of the European green crab.

The project proposes to infect an equal number of five species of crabs native to the east and west coast of the United States. All crabs will be selected at similar developmental stage and size. They will be infected at various stages of development and be allowed to grow to full maturity. The crabs will be housed in separate aquarium tanks throughout over a course of two years.

Barbee expects that the S. carcini will infect all five species of crab that the study will test, but will exhibit a preference for the invasive European green crab. Therefore depending on how much S. carcini infects other species, S. carcini may or may not prove to be an effective bio-control for the European green crab.

Besides S. carcini, Barbee points out that there are other possible methods to eliminate green crab, such as through the use of the U.S.-native adult blue crab, which will prey on the smaller European green crab. However, Barbee explains that the “parasite is a more effective castrator of green crab.” Similarly, because the European green crabs “are so small, there is no market for using them as food.”

In terms of possible health issues that the parasite might pose on humans, Barbee assures that S. carcini cannot affect humans, because it manifests specifically in the fold of the crab’s underside.

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.