Give Them A Taste of their Own Medicine

February 8, 2010

Ben Berg

Chemoecology 8.10.2009

Since their introduction to mainland Australia in 1935, the cane toad (Bufo marinus) has significantly decreased biodiversity amongst reptiles in Australia.  Scientists are now growing desperate in their attempts to limit the growth of this species.  Researcher Mattias Hagman conducted experiments involving biological control mechanisms to fight the toad invasion.

Working in conjunction with Team Bufo (a team of cane toad researchers) and receiving funding from the Australian government, Hagman tested lab results that suggested that a pheromone produced by larval toads lowered survival rates.  Toad larvae were placed into two groups in outdoor ponds, and the treatment group was exposed to the pheromone.  The pheromone, which is emitted by injured larvae to alert other individuals, caused the tadpoles to undergo accelerated metamorphosis, causing a smaller body size and reducing survivorship by 50%.  While this significantly effected cane toad populations, it appeared to have no effect on native species.  The authors have called for follow-up research on the topic.

Ugliness is More Than Skin Deep

February 8, 2010

Freshwater Biology doi:10.1111/j.1365-2427.2009.02247.x (2009)

Didymosphenia geminata, more commonly known as “rock snot”, is considered a serious invasive species. More than just decreasing an ecosystem’s aesthetic appeal, didymo may, according to a recent study, affect the biological community of the invaded territory.

Cathy Kilroy of the New Zealand National Institute of Water and Atmospheric Research Limited and her colleagues studied the effect of didymo on periphyton biomass, invertebrate community diversity and composition, and overall taxon richness. The team performed studies in three different rivers, one dammed, one unregulated but lake-fed, and one unregulated with no lakes. Statistical analysis of the results indicated that the presence of didymo led to an increase in periphyton biomass and invertebrate density, as well as a shift and homogenization of the invertebrate community. The data did not, however, indicate any decrease in overall taxon richness or species diversity. Nonetheless, the fact that didymo has clearly measurable effects suggests that it could create problems in some environments.

Lionfish of the Oceans

February 7, 2010

Mar Ecol Prog Ser doi: 10.3354/meps07620

Invasive species often oust indigenous species from their native locations. Experiments on the movement of the Indo-Pacific lionfish (Pterois volitans) and the recruitment of native fishes suggest that the lionfish is already having substantial negative effect on the coral reefs in the Atlantic Ocean.

Mark Albins and Mark Hixon of Oregon State University used concrete constructed artificial reefs to study the difference of native fish recruitment between reefs that the authors transplanted a single lionfish, from control reefs where there was no lionfish transplantation. The results were that there was a significant decrease (average 79%) in native fish population at reefs with the lionfish from reefs that did not. According to the authors, stomach content analysis showed that the reduction in recruitment was definitely the result of lionfish predation on native species and that strategic control of lionfish need to be implemented quickly.

Pesty Snails

February 7, 2010

Biological Control on Snails

Biological Invasions. doi 10.1007/s10530-008-9378-z (2009)

Indigenous to South America, the golden apple snail (Pomacea canaliculata) has invaded the agricultural and wild areas of several Asian countries.  As an invasive species, the golden apple snail is a pest in the agricultural wetlands of Asia, causing major damage to rice production.  Due to the gold apple snail’s rapid growth and reproduction, they have posed a great threat to the Asian population.

In response to this growing threat, Pak Ki Wong and his colleagues of Hong Kong Baptist University have experimented on the use of common carp (Cyprinus Carpio) as a biological control agent against the invading snail.  Throughout a two month experiment, Wong “quantified the impact of common carp” on several species of snails as well as noting the impacts of the carp on non-targeted aquatic plants and animals.  The common carp was shown to be an effective biological control agent against the golden apple snail, however, necessary precautions should be carried out due to the potential of the common carp “to reduce wetland floral and faunal diversity.”

Jeremy Joven

Invasion By Distribution

February 7, 2010

Invasion By Distribution

BioScience doi: 10.1641/0006-3568(2004)

Zebra mussels have been a devastating problem with the expansion and economic problems in six continents on Earth. Experiments on the zebra mussel, considered one of the most detrimental invasive species, suggest that the potential of the distribution is very high except for the western United States.

John M. Drake and Jonathan M. Bossenbroek measured eleven environmental factors that determine the distribution of the zebra mussels. These are average annual temperature, frost frequency, annual precipitation, solar radiation, minimum temperature, and maximum temperature, bedrock and surface geology, elevation, flow accumulation, and slope. The team then inputted these variables into a genetic algorithm to find potential growth with the zebra mussels’ current distribution. Drake and Bossenbroek state that even though the probability of the transfer in the west is lower than the rest of the states, there is still a good risk due to recreational boaters, which is a focus that should be prevented.

Opportunistic Invaders

February 7, 2010

Opportunistic Invaders

Crustaceana 82, 703-720 (2009)

One of the deciding factors of whether an exotic species will thrive in a given environment is its ability to find sufficient nutrients. The killer shrimp, (Dikerogammarus villosus), a species that originated in the Ponto-Caspian region, is currently invading areas of Europe. This species shows all the signs of a generalist feeder and may be able to invade the United States if given the opportunity. Dirk Platvoet of the University of Amsterdam and his colleagues from around the world have analyzed the feeding behavior of the killer shrimp. They have found that the shrimp is able to gain nutrition from a multitude of sources, including “detritus feeding, grazing, particle feeding, coprophagy, predation on benthic and free swimming invertebrates, predation on fish eggs and larvae and feeding on byssus threads of zebra mussels.” This ability makes the shrimp a threat to bodies of water everywhere.

Nile Tilapia: Dangerous Invaders

February 7, 2010

Nile tilapia, originally from Eurasia and Africa, is a very dangerous invasive species according to Cleber C. Figueredo and Alessandra Giani of the Federal University of Minas Gerais in Brazil because of its significant impact on ecosystems that it invades. Furthermore, it has tremendous potential to spread even further throughout the United States and the rest of the world.

Their goal was to determine what impact that the tilapia had on several ecosystems in Brazil terms of water condition and the phytoplankton community. In their study, the researchers discovered that Nile tilapia have increased the quantity of nitrogen and phosphorus in the water. Furthermore, they have changed algal composition, biomass, as well as water quality. Most importantly, Figueredo and Giani urge caution when tilapia are used in aquaculture so as to prevent extreme environmental problems for native species.

Eel Eradication

February 6, 2010

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.

Et tu, Weevil?

February 6, 2010

J. Aquat. Plant Manage 38: 78-81 (2000)

A study led by Robert P. Creed, Jr., of Appalachian State University investigates the use of biological control to restrain the spread of Myriophyllum spicatum, better known as the Eurasian watermilfoil. This aquatic plant has invaded lakes across North America, and scientists are examining the effects of the North American weevil (Euhrychiopsis lecontei) on watermilfoil on 4 environmental levels ranging from the individual plant to entire geographic regions. On the smallest scale, that of an individual plant, weevil larvae damage meristems, which hinders stem growth, and both larvae and pupae injure vascular tissue, preventing roots from getting nonstructural carbohydrates. Also, scientists found that weevils can make watermilfoil beds collapse in lakes, but the precise weevil density to cause this is uncertain. More research concerning aquatic predators, the nutrient content in sediment, and the regional climate is necessary. Creed concludes that further investigation is crucial at all four spatial levels to determine the efficacy of weevil biocontrol on watermilfoil.

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.