Aquatic Invasive Species

Proc. R. Soc. Vol. 276, 2813 – 2818, (2009)

A study done on Australian death adders shows how certain adaptations have become liabilities in reference to the invasion of cane toads. These snakes have adapted to their environments by developing lures on their tails, allowing them to attract more agile prey, and they have a delayed ingestion process, which allows them to circumvent the dangers of natural toxins.

Cane toads, however, pose a threat to these reptiles. Listed as a “top-ten global invader”, they are slowly decreasing Australian adder populations. Cane toads are typically bigger than native frogs, making it more attractive for adders to lure them in. They also move in slower, shorter hops, increasing their availability as prey. However, their toxins remain active for a long time after their death, increasing adder fatalities. More than half of the adders who tried to eat the toads died as a consequence. Cane toads are not only harming adders, but other Australian wildlife that typically prey on toads as well.

Chris Rzeznik

Selective destruction of certain lamprey subpopulations may be more effective than trying to destroy entire populations of the invaders. A new approach to lamprey control may both save money and eventually become more effective than current efforts of lampricide in the Great Lakes area.

Gretchen J.A. Hansen and Michael Jones of Michigan State University have developed a model to determine the efficacy of targeting streams connected to the Great Lakes for lampricide and control of the sea lamprey population. This model targets streams with large numbers of the young form of the invader. By targeting these streams rather than the lamprey population at large, Hansen and Jones calculate that the effect on the population is the same for less money. With more resources and time, the team claims that the fight against lampreys can become more efficient as money that would be used for general lampricide can be spent to more accurately target lampreys for selective destruction.

Hansen and Jones. Canadian Journal of Fisheries and Aquatic Sciences. doi:10.1139/F08-153 (2008)

Diversity Distrib. 16, 132-143 (2010)

Hull fouling can be an important method of transport of aquatic species to areas where they can become invasive all around the world. However, Its importance in freshwater habitats is not understood very well.

Fransisco Sylvester and Hugh J. MacIsaac from the University of Windsor looked at non-indigenous species transported through hull fouling to the Great Lakes to see if there was a risk of invasion. They took samples from surfaces of over 20 vessels that arrived in the Great Lakes and sorted and identified the invertebrates present. While they found over 170,000 invertebrates per ship most of these were freshwater species already in the Great Lakes. Of the species that they found not already in the Great Lakes, only one of these was in good condition.  Their conclusions were that hull fouling seems to pose of low risk for introducing invasive species into the Great Lakes.

Tara Porter

Biological Invasions 9, 837-848 (2007)

Some invasive species, such as the European green crab, Carcinus maenas, are able to invade new environments because of brute strength.  In a study conducted by a team of researchers from Rutgers University and Bloomfield College, C. maenas was tested to see how it fared in physical competition with other crab species.

Upon comparing the feeding habits and defensive and agnostic behaviors of C. maenas, another invasive species of crab, and the native blue crab, researchers found that, in addition to finding and consuming food more quickly than either other species, C. maenas is able to steal food from other crabs. It is also more likely to win fights, regardless of the initiator.  Exceptions to these observations may be seen in the European green crab’s interactions with adult blue crab, the only group of crab possessing stronger carapaces than those of C. maenas. Established populations of adult blue crab may be able to contain the threat of C. maenas invasion.

Journal of Experimental Marine Biology and Ecology doi: 10.1016/j.jembe.2009.04.012 (2009)

The Chinese mitten crab Eriocheir sinensis is native to estuaries and freshwater on Asia’s eastern coast, but in the early 1900s, invasive populations of this species began developing in northern Europe. In a study conducted by Ana I. Dittel and Charles E. Epifanio at the University of Delaware, researchers found that the crab poses not only ecological dangers, but economic ones as well. The crab’s biological processes like burrowing, migration and feeding harm stream banks and levees, while disturbing fishing activities and irrigation.

This species usually invades through ballast water, but also in some cases through ethnic markets and the aquarium industry. One of the most recently-established invasive populations of the crab inhabits the San Francisco Bay. New populations have emerged on the eastern US coast in the Chesapeake and Delaware Bays, which reportedly contain breeding females. Thus, the crab’s ability to spread rapidly and its wide-ranging detrimental impacts illustrate its increasing threat to estuaries and freshwater across the US.

Emilia Rybak

Estuaries and Coasts Vol. 30, p.469-481 (June 2007)

Phragmites australis (common reed) has caused devastating ecological disturbances to tidal marshes, particularly those in the Chesapeake Bay. Studies conducted on Phragmites abundance in the Chesapeake region are generally small-scale. Ryan King and colleagues at Baylor University performed a scaled-up study to determine the effects of urbanization on Phragmites abundance in wetlands in and adjacent to the Chesapeake Bay. By performing vegetation surveys over a large sample area accompanied by geographic and statistical analysis, King et. al. found that Phragmites abundance was markedly higher in areas with greater levels of both urban-suburban and agricultural development suggesting that development is “at least partially responsible for patterns of invasion across the Chesapeake Bay.” Salinity as well as geographic location may also play a role in determining Phragmites’ invasive success in the Chesapeake. The authors encourage further study of development, salinity, and geography in relation to Phragmites growth in coastal wetlands, as Phragmites invasion is indicative of irreversible ecological change in these wetlands.

Scott Rong

Nature Chem. Biol. 10.2.2005

Lampreys To Be Lured Away By Pheromones.

Ecologist Peter Sorenson, chemist Thomas Hoye, and colleagues at the University of Minnesota have developed artificial chemicals that can lure invasive lampreys to spawn up stream, forcing them out of the Laurentian Great Lakes. Lampreys, a parasitic species, colonized the Great Lakes of North America over hundred years ago and have caused great havoc in the fishing industry. Sorenson and Hoye discovered that larval lampreys emit subtle pheromones that lead adult lampreys to proper breeding grounds. The most active compound in this perfume is squalamine, an antibiotic excreted by sharks. The scent is so potent that lampreys can follow a single milligram of this compound in five Olympic swimming pools of water. The researchers have synthesized squalamine in the laboratory and have teamed with the US Fish and Wildlife Service to bait the lampreys with “fake pheromone” and eradicate the invaders. Conservationists hope to apply this strategy to combat numerous invasive species that navigate via pheromones.

Mar Ecol Prog Ser Vol. 336: 211–223, (2007)

The green porcelain crab (Petrolisthes armatus) is an invasive species in the Southeastern United States that is present in staggering densities of several thousand individuals per square meter.  This has generated some concern among ecologists as the crabs are most common in the oyster reef habitats that form the backbone of the area’s marine ecosystem.  Research by Amanda Hollebone at the Georgia Institute of Technology has provided insight into how this non-native species is able to sustain such population densities.  

Hollebone sampled P. armatus populations throughout its new range and found that the females were reproducing at smaller sizes than in the native range.  In addition, she found that the percentage of reproducing females was similar in both ranges despite much higher population densities in the invaded regions.  These results suggest that the expanded P. armatus populations are more than capable of sustaining themselves through reproduction without the support of future immigrations.

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.

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.