The Zebra Mussel Invasion of the Great Lakes and its Ecological and Economic Impacts

image from: 
http://www.lakegeorge.net/images/zebra_mussel_toon.gif

After being accidentally introduced into Lake St. Clair via ship ballast water from their native Black and Caspian Sea in the late 1980's, the invasive Zebra mussel has caused a severe array of problems both for the human communities surrounding the Great Lakes region and the aquatic communities in the Great Lakes.  These tiny little bivalves, due to the fact that a single female can lay up to 1,000,000 eggs a year, have quickly established themselves in the area and have become quite the nuisance, to say the least.  Their impacts are distributed far and wide when examining indirect consequences, but their most direct impacts on the Great Lakes include out-competing native species, over-filtering the water, and attaching themselves to almost any surface imaginable.  Now, all these things might not seem like such a big deal, but indirectly, they pose serious and dire problems to life as we know it surrounding the Great Lakes.

Image from: http://www.learner.org/courses/envsci/visual/img_med/zebra_mussels.jpg

Because of their strong byssal fibers, the zebra mussel can attach to most hard surfaces and have been known to cling to shopping carts, water pipes, and boats.  In the case of water pipes, they cannot serve their given purpose if they have a bunch of little mussels taking up space inside and clogging the flow, so they need to be removed which can be costly and never-ending.  Maintenance crews will have to come back time and time again to remove pesky mussels from clogged water intake pipes for electric power generation and municipal water filtering facilities.  This can typically cost a lot of money; $3.1 billion between 1993-1999 for the power industry alone, to be exact (source).  Other methods of getting rid of the Zebra mussel include chlorine-based chemical controls, which can be effective in inducing mortality but yield dangerous environmental consequences, such as killing other non-target organisms, bioaccumulation, and the release of known carcinogens into the ecosystem.

Besides affecting areas of human concern in the form of economic damages and management difficulties, the establishment of Zebra mussels in the Great Lakes ecosystem has had severe detrimental effects on the local ecology and has even lead to the disruption of the local food web. 

One of the most apparent ecological effects that the zebra mussel has had on the Great Lakes ecosystem is the manner in which it filters the lake water.  Since they are filter-feeders, a single Zebra mussel can filter up to a quart of water a day.  Multiply that by a number on the order of millions and it becomes possible to filter all of the water in a lake or stream in just one day.  This has yielded much clearer lakes, which may seem great and beautiful and everything, but in actuality the increased solar penetration, along with other factors, has actually generated massive bright green toxic algae blooms.  Lake Erie, pictured below, has fallen victim to said algae blooms.  The Zebra mussel filters out most plankton and algal species, but chooses to leave behind a certain cyanobacteria called microcystis. This macroalgal species, mixed with their newly acquired lack of competition and phosphorous run-off from local farms and industry, is able to thrive.  Their eventual decay can deplete oxygen from the water and create "dead zones" where oxygen levels are so low that fish can't even survive.  (That's not good at all)

Image from: http://eoimages.gsfc.nasa.gov/images
/imagerecords/76000/76127/lakeerie_tm5_2011278.jpg

The other major effect that the Zebra mussel has been shown to inflict upon colonization sites lies in its ability to out-compete a tiny little shrimp-like amphipod called Diporeia.  Since around the time that zebra mussels were discovered in the great lakes, the numbers of Diporeia have simply plummeted  These little shrimp-like substances are a very important player in the Great Lakes food chain, for they are high in lipids and are a good source of calories for many larger aquatic organisms in the ecosystem.   

Image from: http://www.iaglr.org/jglr/db/show_article.php?
file_name=2001/num4/27_4_423-433.pdf

This survey, taken from Lake Ontario (Table 1), shows sharp Diporeia declines in most samples between 1990 and 1995.  Of the 15 sites sampled, 7 had become completely devoid of the important shrimps, 5 were drastically reduced, and 3 actually showed an increase in Diporeia density. Interestingly enough all of the sites that experienced a total depletion of Diporeia numbers were at depths lower than 50 meters, while those who experienced population increases were all at relatively deeper sites, perhaps hinting at the possibility that water depth is correlated with the stability of a Diporeia population.  

Image from: http://www.iaglr.org/jglr/db/
show_article.php?file_name=2001/num4/27_4_423-433.pdf

As this graph (Fig. 2) shows, the density of Diporeia has quickly decreased to zero in almost all sample sites on Lake Ontario since the zebra mussel was established in 1989, with the exception of the mid-lake sample site.  The Diporeia populations near the shore and in the east side of the lake completely collapsed.  Even after two years of follow up surveying, none were to be found.   The increases in the mid-lake sample site make sense when combined with the numbers from the above table; the mid-lake sites are more likely to have a greater depth than nearshore sites, and thus this would also support the hypothesis that increases in water depth can be linked to increased probability of survival of Diporeia populations.

Since food webs typically function similarly to a stack of blocks, the removal of a single lower block can sometimes cause the whole stack to collapse.  Since the decline of Diporeia, a whole slew of other larger aquatic organisms have hopped on the band-wagon and started to decline in numbers as well.  The period between 1988 and 1996 saw a 95% decline in Lake Ontario lake trout and slimy sculpin numbers, while smelt stocks have also been heavily damaged by this lack of suitable food.  In Lake Erie, rainbow smelt and whitefish have seen dramatic declines.

In Lake Michigan, some fish populations are being forced to switch their diet from Diporeia to Zebra Mussels!  On first thought, this doesn't sound like such a bad thing because it shows that it is possible for native species to predate upon and hopefully contribute to the eradication of these hellishly invasive mollusks, but an examination into the caloric content of the Zebra Mussel will show that they offer little to no energetic value to their consumers.  One of the few things that they do seem to accomplish for those fish who do choose to consume them though, is that they take up space in their digestive tract and leave little room for food-bits that actually contain energy.  Thomas Nalepa, a research biologist at the Great Lakes Environmental Research Lab, said that "the [whitefish], whose guts became packed with shell material, were so skinny that fishermen could no longer get a fillet off them."
Because of this, the alewife fish has also seen a 23% reduction in energy density between pre-invasion and post-invasion surveys, which has caused the Chinook salmon, who prey upon them, to need to consume a corresponding 22% more alewives than before the mussel invasion to attain ideal body weights.

Any way you look at it, these Zebra mussels are posing quite the problem for the Great Lakes region, as well as everywhere else they are spreading to.  While the easiest and closest to home problems are easy to conceptualize in monetary terms, the bigger changes that they are causing in the ecosystem should be cause for larger alarm.  The difficulty of removing them only adds to this gargantuan problem.  Unless a way to successfully eradicate established populations and halt their spread can be found, we just might have to get used to these tiny rapidly-breeding pests and the non-refundable ecological collapses that accompany them.

More Reading:
Ronald Dermott - Sudden Disappearance of the Amphipod Diporeia from Eastern Lake Ontario, 1993–1995

Zebra Mussels - NationalAtlas.gov

The infamous cane toad: Is 85 years long enough to wait for Australian citizenship?

From the beginning of our modern evolution, we have had a great impact on our environment and the world as a whole. As humans we like to alter the area around us in order to improve our way of life. A good example of this is evident in invasive species. Whether as a piece of home or as a solution to a pest problem, we have a long history of bringing non-native organisms with us as we travel and settle new places. One of the most popular stories of an invasive species is that of the cane toad (Bufo marinus) and Australia (Fig 1).

Figure 1: Bufo marinus (cane toad)

Before I delve into why the cane toads might carry an important message today, it’s important to go over a bit of their history. They were originally introduced into Queensland, Australia from Hawaii (a place where they are also an introduced species) to combat a problem with cane beetles infesting sugar cane crops (Fig. 2: arrow shows site of introduction). While the initial introduction contained only about 100 toads, in the subsequent years over 60,000 toads were introduced into northwest Australia. However, not only did these toads become the poster organism for invasive species, they did little if not nothing to control the sugar cane pests.

Figure 2: Site of initial cane toad introduction

Cane toads are a great example of all the traits that make “good” invasive species. The females lay tens of thousands of eggs a year and are able to lay these eggs in almost any body of water. Not only are these eggs not susceptible to the viruses or predators present in their native habitat, but the tadpoles possess a toxin that kills many of the animals that try to eat them. However, it isn’t just the tadpoles that possess this deadly defense mechanism, the toxin coats every life stage of the toad and provides a huge obstacle for any potential predators. Finally cane toads will eat just about anything both dead and alive, which makes them a menace to any native insects and small animals species.

These traits combined with their ability to survive in a wide range of climates have made them especially successful in Australia. While once just 60,000 toads on a small section of the coast, there are now more than 200 million toads spread over almost all of Queensland and into the Northern Territory. Figure 3 shows the spread of cane toads between 1940 and 1980. Due to their toxic coating, the toads have led to large decreases in many reptile, bird, mammal and rodent populations. In addition, their strong competitive edge has led to reductions in native toad species. Overall, the toads have had a huge impact on the biodiversity in their introduced region and are hypothesized to spread further into currently toad-free areas of west, and perhaps even south Australia.

Figure 3: Spread of cane toads from 1940-1980

While people have tried and proposed many methods for controlling the cane toad populations in Australia, nothing has been successful so far. Physical removal of toads merely provides the remaining toads with an even further competitive edge by removing intraspecific competition. Scientists have proposed the idea of genetically engineering a cane toad specific virus and introducing it into the population, but a method like that requires extensive funding, research and time. Professor Peter Koopman’s work on the sex chromosomes of the toad has provided an interesting idea for biological control. He has proposed a method by which genetically modified male cane toads that produce only male offspring could be introduced into the population and over time skew the sex ratio such that the cane toads would no longer be an issue. While ideas such as Koopman’s are inspired and quite creative, they too require large amounts of time and money in order to put them into action.

However, there might be hope. Scientists are starting to see changes in the way native Australian species interact with their new toad neighbor. Birds that once died from ingesting the cane toads are now selectively preying on the less toxic parts of the toad like the stomach. In addition, some native snake species have taken to consuming smaller cane toads and avoiding larger ones, which by extension have more toxin covering their bodies. Even more interestingly, young cane toads are more susceptible to the native meat ants as they do not possess the adaptive traits that allow for escape from these predators like their native toad counterparts.

I find this trend in adaptive behaviors in native species very interesting. After all, cane toads have been present in Australia for over 85 years. While I don’t think anyone would argue that they have not been a destructive force, over time perhaps their effect on the ecosystem is becoming more complicated. As time passes and native species adapt to the presence of the cane toad, is the toad considered part of the local habitat, or is it still a target for removal? Could removing an invasive species long after it was first introduced be potentially detrimental?

Imagine the Pacific Coast, with its large dunes rooted by European beach grass (Fig. 4) This grass, introduced on the west coast in the late 19th century has allowed for the stabilization of the dunes and the ability for other plant species to colonize closer to the coast line. While an invasive species, the eradication of this grass that has existed on our beach for over 100 years could have unforeseen effects not only on our man made infrastructure, but also on the ecosystems both in and around the dunes themselves.

Figure 4: European beach grass along an American coast

I think the same might be true for the cane toads. They have not only become part of Australia to some of the people who live there (as seen in Cane Toads: An Unnatural History), but they have caused both known and possibly unknown adaptive changes in the species around them. Not only is any method to remove these toads going to be costly in terms of time and resources, but it could also have unforeseen ecological effects.

Personally, I think that invasive species are a huge problem and that there are plenty of new, or relatively new harmful species that we could be focusing our time, money and energy to eradicate and control. In addition, we should be trying to find ways to avoid spreading more potentially invasive species by monitoring trade and rethinking some classic ideas around pest management. However, after 85 or 100 or even 200 years of unsuccessful management methods, perhaps devoting more time and research on an established invader will do more harm than good. By trying to control cane toads in Australia, we could be missing opportunities to combat invasive species that haven’t fully actualized their destructive potential.

Related Links:
Wikipedia: Cane Toads in Australia
Cane Toads: An Unnatural History: Youtube

Figure Sources:
Figure 1: Photo taken by Duncan Mclean
Figure 2: Shanmuganathan et. al. 2007 (see references)
Figure 3: Wikipedia
Figure 4: Photo from Oregon State University. Link


References:

Brown, Gregory P., Matthew J. Greenlees, Richard Shine and Georgia Ward-Fear (2009): “Maladaptive Traits in Invasive Species: in Australia, Cane Toads Are More Vulnerable to Predatory Ants than Are Native Frogs.” Functional Ecology, Vol. 23,. pp. 559-568

Koopman, P. (2006, June). Daughterless cane toads. Paper presented at Invasive animals CRC/CSIRO/Qld NRM&W cane toad workshop, Brisbane, Australia.

Phillips, B. L., & Shine, R. (2006). Adapting to an invasive species: Toxic cane toads induce mophological change in Australian snakes. Proceedings of the National Academy of the Sciences, 101(49), 17150-17155.

Shanmuganathan, T., Pallister, J., Doody, S., McCallum, H., Robinson, T., Sheppard, A., Hardy, C., & Halliday, D. (2010). Biological control of the cane toad in Australia: A review. Animal conservation, 13(s1), 16-23.

Tyler, M. J. (1998). Australian frogs a natural history. Ithaca, NY: Cornell University Press.

Control of Tansy Ragwort Invasion in the Pacific Northwest

Senecio jacobaea, more commonly known as tansy ragwort, is an invasive, toxic biennial weed that has been a serious weed problem in western Oregon, Washington, and northern California.  It was first reported in British Columbia in 1912, and in Portland in 1922.  In the Pacific Northwest it is often found in pastures and along roads and trails.  Ragwort has been declared a noxious weed in many areas and control is required in many selected counties.  This invasive weed is poisonous and lethal to native plants and animals, detrimental to soil quality, is a big hindrance to local economies, and poses a threat to the health of people in the community.

Figure 2. Tansy Ragwort once the flowering stems bolt

Figure 1. Tansy Ragwort in the rosette stage

Tansy ragwort is classified as a biennial herb.  As a biennial, the first year is spent in a rosette stage.  During the second year, the flowering stems bolt.  Initial infestation is by seed.  A large plant may produce as many as 150,000seeds, and the seeds can lie dormant for up to 15 years, which is why tansy ragwort is a very difficult plant to control and eradicate.  Furthermore, physical disturbances such as mowing or grazing often cause the plant to behave as a perennial [E. Coombs et. al].

A major issue with tansy ragwort is that it is noxious and lethal to many native plants and species in the communities that it invades.  The entire plant is toxic, but the most toxic part of the herb is the leaves, which generally are eaten while an animal forages for grasses and other target plants that grow near and around the tansy ragwort.  If the leaves dry out they still maintain their toxicity but not the bitter taste, and when mixed with hay or other silage it is not possible for the animal to detect or avoid the tansy ragwort when grazing or feeding.  Thus they unknowingly continue to ingest the tansy ragwort.  Tansy ragwort contains six different pyrrolizidine alkaloids that are converted to toxic pyrroles in the liverduring metabolism.  These pyrroles are generally both toxic and carcinogenic.

Figure 3. Chemical structure of pyrrolizidine alkaloids. Jacobine is one of the major pyrrolizidine alkaloids found in ragwort.

The damage to the liver is both irreversible and cumulative, and will kill the animal. Poisoning can also occur in young animals that are still feeding on the mother's milk, as alkaloids can accumulate in the milk and be passed from mother to young [E. Coombs et al].  Cattle and horses are the most vulnerable to poisoning but tansy ragwort has also negatively impacted population numbers of deer, pigs and goats. Ragwort fed  to goats at 1 percent of their body weight for 25 days, during lactation (for a total of 125% of the goat's body weight) caused abortions and subsequent death of  the does [Bedell et al]. Livestock are highly affected by tansy ragwort as the weed is very prevalent in pasture land.

Figure 4. Oregon Department of Agriculture Regional Survey. Average flowering plant density and number of cattle deaths diagnosed as pyrrolizidine poisoning at the OSU Veterinary Diagnostic Laboratory.

Figure 5. Cinnabar Moth larvae 

To get rid of ragwort, ideally biological control is preferred to spraying herbicides.  Use of cinnabar moths and adult flea beetles to control tansy ragwort in tandem has worked wonders in Oregon.  The cinnabar moth (Tyria  jacobaeae), was introduced into the Pacific Northwest in 1960 and is now widespread throughout the ragwort-infested areas west of the Cascade mountains [Bedell]. 

Figure 6. Flea Beetle

Figure 7. Cinnabar Moth

The larvae feed on the foliage and flowers and can completely defoliate the plant in large numbers.  However they only provide partial control of the tansy ragwort as they are relatively useless in controlling the rosettes.  The ragwort flea beetle (Longitarsus jacobaeae) eat the foliage during the fall, and the larvae mine the roots of the rosettes and kill plants in the winter and spring.  The beetles augments the cinnabar larval damage, coming at a time when the cinnabar moth is inactive [Bedell].

Ragwort control has significant economic benefits.  During the 1980s when the infestation was extremely bad, Oregonians reported an annual estimated loss of $4 million dollars from their livestock grazing on infested pastures [Radtke et. al].  Oregon legislature funded a measure that included a biological control program for tansy ragwort, which eventually curbed animal losses by $3.73 million annually [Coombs et al].  The benefit of biological control is reflected in a much lower livestock mortality rate, healthier livestock from purer feed, better crop yields, and a reduced expenditure on reactionary weed control methods, which accounted for another $2.12 million annually in savings [Coombs et al].  The biological control programs have cost around $240,000 annually in recent years [Coombs et al], and there clearly is a net benefit by saving farmers from millions of dollars in losses.  This has a positive effect on the entire community - market prices of local produce are a lot lower than they would be if farmers continued to suffer $4 million annually.  Furthermore, based on the dollar estimates over the 19 years, the calculated benefit-to-cost ratio for the entire state varied from 13:1 to 15:1, depending on the interest rate used.  The annual rate of return to the state of Oregon is greater than 80%, [Coombs et. al] which shows that this is a very cost-effective and necessary measure. 

Figure 8.  Percentages of annual savings due to control of tansy ragwort in Western Oregon.

Of course, there are many nonmonetary factors that justify this measure in itself. Reduction in the use of herbicides, improving wildlife habitat, and improving quality of life of livestock are all important reasons to take into account that cannot be quantified fiscally.  Control of tansy ragwort is essential for both economic and ecological reasons, as the entire community is adversely affected through the biotic and abiotic effects that the invasive weed has.

For More Information See

Stevens County Noxious Weed Control Board

King County Noxious Weeds

Pacific Northwest Weed Control Handbook

Image Sources

1. http://www.co.stevens.wa.us/weedboard/htm_weed/tr.htm
2. http://www.kingcounty.gov/environment/animalsAndPlants/noxious-weeds/weed-identification/tansy-ragwort.aspx
3. http://www.biomedcentral.com/1746-6148/4/30/figure/F1?highres=y
4. http://whatcom.wsu.edu/mgtemp/classes/weeds/PNW175.pdf
5. http://www.treknature.com/gallery/photo640.htm
6. http://www.agf.gov.bc.ca/cropprot/tansy.htm
7. http://www.bugsandweeds.co.uk/moths%20p2.html
8. http://whatcom.wsu.edu/mgtemp/classes/weeds/PNW175.pdf

References

1. Bedell, Thomas E. et al. (1981) Print. Pasture Management for Control of Tansy Ragwort. Pacific Northwest Cooperative Extension Bulletin.
2. Coombs, E., et al. (1997).  Tansy Ragwort. Pacific Northwest Weed Control Handbook 175
3. Radtke, H et al.  1993.  An Economic Evaluation of Biological Control of Tansy Ragwort.  Oregon Department of Agriculture State Weed Board.  PP 31
4. Sweeney, S.J. and K.E. Neiman, Jr., K.A. Lakey.  1992.  Alternative Control of Tansy Ragwort.  Prepared for Seattle City Light, Environmental Affairs Division, Parametrix, Inc.  Final Report of 1986 - 1991.
5. Washington State Noxious Weed Control Board. (Dec. 1997). Web. Written Findings of the Washington State Noxious Weed Control Board. 

Globalization and the spread of Invasive Species

Imagine this, you find yourself in a dark almost pitch black enclosed space, surrounded by unfamiliar terrain and objects. The air tastes and feels different than you’re used to.  The sounds you have heard every day no long permeate the air around you, instead there is nothing but a repetitive splashing sound. The world around you rocks harmoniously swaying back and forth. These sights, sounds, and motions are all you know for the next few days, although time seems to slip away. Suddenly you are jarred away from this strange world as sunlight strikes your eyes, after adjusting for a few moments you realize you in the storage cargo of a boat. As soon as you possibly can you escape, leaving behind the boat that held you captive. Around you now, not unlike the boat, is not the home you once knew, instead you find a world that is full of food, delicious food. And much to your delight you find you were not the only one of your kind to have been transported, in fact a lot of you were aboard the ship. Suddenly a vicious hunger grips you and the other members of your home land, you begin to travel inward and eat all the food around you, and it pleases you that in this new world no one is trying to attack you, and so you begin to reproduce and eat and reproduce and eat. This story may seem like some sort of science fiction novel, but if you have not already guessed this is the tale of invasive species one that has played out at an increasing rate because of modern globalization.
 Does this map show products being shipped or travel destinations for invasive species? 

                Since the last 200 years global trade has been steadily increasing, this has been dueto the fact that economies have been growing. And not only have economies been growing but we have developed better technology that allow for bigger, stronger, and faster methods of transportation as well as technology that allows for easier excavation/depletion of resources. Since the first person set sail invasive species most likely came aboard as well, but within the last 50 years the scope of trade has increased by so much that invasive species have begun to travel to new lands, whether by accident or intentionally by humans, at an alarming rate. Because of globalization a healthy portion of invasive species has been wreaking havoc on the lands they have come into contact with. Increased global trade leads to more product shipping and it is within these products that some species travel, much like stowaways. Others cling the ship themselves to move from one ocean to the next, and therein lies the problem. Comparing the two graphs below it can be seen that as global shipping has increased so to have invasive species.

                                The graph above shows the increase in global shipping, this has increased as global economies increase

                                This graph shows the increase in invasive species since 1500, showing a huge increase in the last 100 years

     
  Invasive species alter ecosystem resulting in a variety of negative consequences.  One of the biggest issues is that invasive species out compete native species, this results in the displacement of native species, if not extinction. This can have huge effects on the invaded ecosystem, if the native species that is driven out is a keystone species then the loss of that species can cause a trophic cascade, resulting in an even greater reduction in species within the area. Hence invasive species can lead to a reduction in biodiversity. This reduction in biodiversity can lead to a reduction in certain ecosystem services provided by the land, this is another problem related to invasive species. To fully see the scope that invasives can have it is best to highlight a few prominent cases of invaders.

                One of the most beautiful aspects of science to me is when two species co-evolve resulting in the dependence of one on the other. These mutualistic relationships evolve because somewhere in time the species began to have an increase in fitness when the two worked together. One stunning example of co-evolution is in South Africa where native species of ants carry and thus disperse the seeds of native plants; this mutualistic interaction is known as myrmecochory. The ants gain a food source, because what they actually are attracted to are food bodies attached externally to the seed, and the plants have their seeds dispersed. But in last the few decades this wonderful balance has been disrupted by an invasive species that was brought to South Africa on cargo ships, the invader is the Argentine ant, Iridomyrmex humilis. Argentine ants out compete native ants and they even attack and kill other species of ants. Where the Argentine ant is invasive it has been replacing indigenous species of ants and South Africa is no different. A study carried out by W. Bond and P. Slingsby looked at how the Argentine ant, by replacing indigenous ants, disrupts a coevolved dispersal system and reduces seedling establishment. The study found that the Argentine ant impacted the local vegetation negatively. They found that when native ants were exposed toseeds the rate of seed removal was 100% by the end of the first day, indicatingthat native ants are effective seed dispersers. The Argentine ants, on theother hand, only removed about 44% of the seeds after the first day; this showsa huge decline in the seed dispersal. The results were that Argentine ants caused a decline in approximately 170 species of plants. This decline was due to the fact that Argentine ants do not disperse seeds as far; do not gather as many seeds thus leaving them out in the open to be consumed by birds and rodents, and also by eliminating native ant species that do successfully disperse plant seeds. Like many invasive species brought about by globalization these ants lead to a decrease in native species.

The Argentine ant

                Another invasive species, the Asian longhorned beetle, was introduced to the United States by global trade with china. The Asian long horned beetle is native to eastern China, where it has recently has become a pest. The species was first reported in the United States in 1996 in a port in New York City. The Asian longhorned beetle was transported in solid wood packing materials, such as cargo crates, from Chinese ships. Once it escaped from the cargo ship it began to infest a large number of trees in the United States. The Asian longhorned beetle eats an enormous variety of tree species, effectively killing the tree. The adult Asian longhorned beetles does not do much more than chomp on a few twigs, the larvae however do a sever amount of damage. The larvae eat their way into the center of the tree eating away at the cambium and vascular tissues, after a year of burrowing they then eat their way out where they metamorphosis into an adult. The only method of removing the Asian longhorned beetle has been to cut down infested trees. In the United States approximately 42,000 treeshave been cut down and about 866,000 have been treated with insecticides tostop spread infection. This has cost the United States close to 375 milliondollars.

Asian Longhorned beetle

                These case studies exemplify the devastating environmental and economic impacts that the spread of invasives can have, and this spread is only worsened by increased global imports and exports. We know that invasive species are showing an upward trend because of increasing globalization, we know the affects the invasives can have, but what can be done to decrease their spread? The first idea to stop their spread would be to stop global trade, this however is not a reasonable solution. The next step is to stop invasives from getting into non-native lands or water ways. One of the most effective methods to stop invasives from getting into water from ships is called ballast water exchange, in which the tanks of a ship are pumped out and refilled in the open sea. Another method that was created to treat shipments that might contain the Asian Longhorned beetle is described as a phytosanitary measure. This involves a standard for heat treatment and fumigation of wood packaging materials. This standard has been adopted internationally, showing that the global community is beginning to try and combat the spread of invasives.

                Global trade is necessary for economic stability in most developed, and even in a lot of under developed, countries. What is not necessary is the re location of species from one country to another. To help deter this spread we need to develop policies and standards that are strict on detecting invasive species. We need to have the fore sight to search all shipped cargo to see if it contains any unwanted specimen, because even if a shipment has a species that is not invasive now it may become so in future. The negative impacts that invasive species can have is too great for us to not take action, we must take measures to ensure that global trade will no longer negatively impact the environment. So what can the average citizen do to stop invasive species, a few things. First off vote for legislation that will impose stricter security measures on trade ships. Next if you know a product was shipped carrying an invasive, don’t buy it. And most importantly if you see an invasive species in your community inform a local authority on the matter.

Relevant links

Invasive Species: Pathogens of Globalization

http://www.jstor.org/stable/pdfplus/1149643.pdf?acceptTC=true

Trade, Transport and trouble: managing Invasive species in an era of globalization

http://www.uni landau.de/umwelt/study/content/files/archiv/H.Schulz/WS09/Biodiversitaet_und_Naturschutz/Hulme%202009.pdf

Collapse of an Ant-Plant Mutualism

http://www.jstor.org/stable/pdfplus/1938311.pdf?acceptTC=true

Managing Invasive Populations of Asian Longhorned Beetle and Citrus Longhorned Beetle: A Worldwide Perspective

http://ddr.nal.usda.gov/bitstream/10113/36707/1/IND44300067.pdf