Oct
31
Filed Under (SW10) by Natalie Ferguson on 31-10-2010

In 1998, Edward P. Levri from Indiana University studied the how effects the parasite Microphallus has on the behavior of New Zealand mud snails impacts the New Zealand fish, Potamopyrgus antipodavun. The design of his experiment included collecting fish samples from various hours of the day, particularly morning versus evening, and counting the number of infected snails compared to non infected snails. He was able to count the snails present in the fish by first killing them and then examining the guts. Levri found that the fish guts tended to have a significantly higher amount of uninfected snails than infected. These results showed that the behavioral changes the parasite caused the snail made the fish less likely to be in the water during times where the fish population was feeding. These findings show that the parasite does not have a secondary impact on the New Zealand fish.

Oikos 81, 531-537 (1998).

Oct
31

Aquatic Botony 76.3, 259-265 (2003).

Sallie P. Sheldon and Robert P. Creed, Jr. (2003) published findings in Aquatic Botany regarding the success that the biological control agent, Euhrychiopsis lecontei, had in decreasing biomass of the invasive Eurasian water milfoil (Myriophyllum spicatum). Native milfoils were exposed to varied numbers of weevils in a controlled laboratory setting. In vials containing more weevils, the milfoil had lower shoot lengths, highlighting a negative consequence when weevils were overly abundant. However, milfoils exposed to only one or two weevils did not have a significant plant biomass reduction. The experiment also showed that weevils did not hatch on native milfoils, suggesting that the reduced fecundity would leave native species at lower risk of harm. Sheldon and Creed (2003) concluded that E. lecontei are host-specific, and would be an appropriate control option for Eurasian water milfoil.

Oct
11
Filed Under (SW7) by Tyler Lacy on 11-10-2010

Larson (2005) expresses his belief that the much used militaristic language in invasion biology has no place in scholarly articles. He states that even though the metaphors may draw attention to the articles, they are overall ineffective.  Larson argues that the use of this language draws the reader towards a man vs. enemy viewpoint which in turn causes an inaccurate perspective of the problems regarding invasive species. Larson believes that this “us vs. them” way of thinking is an oversimplification of the problem and that it is leading a complete public misunderstanding. One example of this kind of language is found in a blog posted by Brianca King (10-09-2010).  In her paper, Brianca discusses termites and their detrimental effects on building and infrastructure. She states that “When the troops…dumped their crates…the termites began their attack.” (Brianca 2010)  In actuality, the termites did not attack anything, only started eating their natural food, but this militaristic language draws the reader into the article and helps the reader understand that there is a threat.

I agree with Larson’s argument in that militaristic language can lead the reader to have an inaccurate and ineffective viewpoint regarding the fight to control aquatic invasion however I believe that it still must be used. In today’s society, there are very few ways to get public attention and one is to pose a serious threat and treat the problem as if humans were at war with these aquatic invaders. Even if the public, in general, has a faulty perspective on the issue because of the use of militaristic language, I believe that the transaction costs would be much too high and nothing in the field of invasion biology could ever be accomplished if the language were not used. Larson’s arguments may be true, but militaristic language must be kept in invasion biology articles.

References:

Larson, B. M. H. 2005. The war of the roses: demilitarizing invasion biology. Frontiers in Ecology and the Environment 3: 495-500

King, Brianca. Termite Attack!. Aquatic Invasive Species Word Press. October 09, 2010. SW2. http://sites.duke.edu/writing20_12_f2010/2010/09/10/termite-attack/

Sep
24
Filed Under (SW5) by Blair Ballard on 24-09-2010

J. Aquat. Plant Manage. 45: 58-61

Giant salvinia is known as one of the world’s worst weeds. Both biological control as well as chemical control is used to combat the weed. Glyphosate and diquat are proven to be the two most effective chemical control agents used to treat giant salvinia.

Nelson and her colleagues tested different rate and spray volumes of glyphosate to determine the most effective way to control giant salvinia. Despite higher rates initially showing greater reduction of biomass, the final results proved that the most effective and economical way to control giant salvinia was at lower rates and spray volume. The experiment also proved the flexibility of glyphosate as a control agent because it was effective at various rates, therefore reducing the risk of failed treatment. All glyphosate treatment rates showed control of over 95% biomass.

Sep
13
Filed Under (SW3) by Brianca King on 13-09-2010

Water Hyacinth, or Eichhornia crassipes, is among the world’s most noxious invasive weeds (NASA Earth Observatory 2007). The plant arrived in Africa in the late 1800’s and made a home in Africa’s largest lake, Lake Victoria.

Biological control, the use of organisms that are natural predators, parasites, or pathogens to control an environmental pest, was introduced in 1995 and weevils were released onto different parts of Lake Victoria (Wilson et al. 2007). A few years after the introduction of the weevils in 1997 and 1998 El Nino hit and here is where the controversy begins. According to Wilson et al.(2007) the weevils were the main cause for the decline of the Water Hyacinth and El Nino was a small aid to the problem. Weevils reduce the plant buoyancy and allow for bacteria and secondary fungi to cause severe damage to roots (Wilson et al.2007). Williams et al.(2007) says that El Nino had the greater affect on the reduction of the Water Hyacinth by accelerating the decline through direct effects.  El Nino produced a low light climate. Low light levels do not cause instant mortality but prolonged sub-optimal light will reduce growth and reproduction rates and relatively increase the effect of other debilitating influences (Williams et al.2007). Both sides used satellite images to make graphs to support their arguments as well as the work of other researchers. The graphs depicted in each article show the increase and decrease of the Water Hyacinth in Lake Victoria over time.

Williams et al.(2007) provided a better argument for the decline of the Water Hyacinth. The approach taken by Williams et al.(2007) was more realistic in that it did not oversimplify the issue and acknowledged that Lake Victoria is a complex aquatic ecosystem and that any synchronicity across such a large waterbody is unlikely to occur at the biological scale(Williams et al.2007). This was a direct response to the condensed graph provided by Wilson et al.2007 used to show the rise and decline of the Water Hyacinth in Lake Victoria. Williams et al.(2007) also acknowledges that weevils are effective and mentions their success in other situations across the world but makes it clear that El Nino had a more direct effect on the Water Hyacinth population which is evidenced by the graphs in both articles. Furthermore satellite images from the NASA Earth Observatory showed a resurgence of the Water Hyacinth in 2006 proving that Williams et al.(2007) was correct in saying that the weevil population would not stabilize and the Water Hyacinth would return.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
13
Filed Under (SW3) by Max Castillo on 13-09-2010

Ever since first being recorded in 1989, the water hyacinth plant has plagued Lake Victoria in Africa. The plant is causing substantial problems for the local ecosystems, such as reducing fishing levels, threatening biodiversity and tampering with the many transport routes across the lake. Because of these issues, measures to try to reduce the hyacinth’s population have been taken, but much controversy exists questioning whether  man or nature removed the vast majority of the plant from the lake. Much of the debate spawned from two conflicting research articles, which attempted to clarify whether the seasonal El Niño storm had destroyed the hyacinth or if  the introduction of hyacinth-eating weevils caused the plant’s demise.

Wilson et al. first proposed that through biological control the hyacinth populations started decreasing. In their article, they express that the introduction of Neochetina (weevils) was the primary factor in the limitation of the hyacinth. The article does acknowledge the presence of the 1998 El Niño weather pattern however, and does recognize that the increase in waves and water levels played a role (albeit small) in controlling the hyacinth. And although they also do say high cloud levels could also have decreased hyacinth levels, Wilson stands firm that El Niño only propagated the effects of the weevils.

On the other hand, Williams et al. claimed the weevils assisted El Niño. This article believes that if El Niño had not occurred, the weevils never would have controlled hyacinth levels. Williams affirms that while biocontrol through weevils “is an integral part of the future management of Lake Victoria”, lake wide reduction in hyacinth populations resulted from El Niño. Williams also supports this claim with more in-depth studies of the factors mentioned above (cloud level, wave, and water lever) to prove that El Niño nearly wiped out the hyacinth.

While in hindsight we do know that Williams et al. hypothesized correctly (once El Niño subsided hyacinth populations increased once again), I do have to  say that Williams did provide a more convincing argument from the start. Williams provided and researched numerous points that Wilson seemed to look at from the wrong angle, such as water levels and waves. Although both researchers do claim that one would not have been as effective without the other, Williams is successful in convincing me that El Niño played a larger, more important role the reduction of hyacinth levels in the late 90s.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.
Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.
Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
13
Filed Under (SW3) by Steven Blaser on 13-09-2010

According to Wilson et al. (2007), the dominant factor in controlling water hyacinth populations was clearly the weevil. While they admit that the El Nino of 1997/98 could have contributed to the water hyacinth decline, they stubbornly claim that the weevil was solely responsible for the biological control that occurred, biological control that had not been successful in any other lake near the size of Lake Victoria. According to their explanation and their graph, it is clear that water hyacinth’s sustained reduction did not occur until a year after the El Nino occurred (although they cede that populations did begin to decline immediately after the El Nino event for a short period of time).

On the other hand, Williams et al. (2007) takes the opposing viewpoint. First of all, they claim that the lake cannot and should not be “condensed…into a single graph” (8). Then, they attribute the continued control of the water hyacinth population to both the El Nino and the weevils, saying that the combination of the reduction in sunlight, water levels, etc. and the biology control exhibited by the weevils together limited water hyacinth growth. However, without the El Nino, the dramatic reduction in water hyacinth would not have been possible because the weevils could not possibly do the job by themselves, but rather needed the assistance of one of the biggest storms of the century.

In light of satellite imagery, I conclusively agree with Williams et al. (2007). In addition to the more open-mindedness of their argument, Williams et al. (2007) argument accounts for why it is likely that the water hyacinth population relapsed. The satellite imagery shows that water hyacinth came back in full force, spreading and even dominating the entire lake. At the end of Wilson et al. (2007)’s argument, they claim that the weevils are the reason that the water hyacinth had died out and would be the sole preventive cause for them coming back. However, in light of the current evidence, the weevils cannot do the job alone. Rather, there must have been an additional influence that aided in the collapse of the water hyacinth. This cause seems to be the El Nino which Williams et al. (2007) predicted was the major reason for the water hyacinth demise.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
13
Filed Under (SW3) by Michael Zhou on 13-09-2010

Water Hyacinth was brought by botanists to West Africa in the 1980s, and somehow entered Lake Victoria, the second largest fresh water lake in the world, in 1989 (Wilson et al. 2007). The plant spread rapidly due to abundant nutrient as well as lack of natural enemy. It choked Lake Victoria by taking up tens of thousands of hectares of the water surface, severely impacting local biodiversity and fishing economy. Continuous efforts were made in order to fight this invasive species. A release of weevils had been adopted as a biocontrol measure since 1995. The water hyacinth population was reduced greatly since 1999, but in 2007, the invasion returned as seen from NASA’s MODIS satellite images (NASA Earth Observatory 2007).

There used to be a debate on what exactly caused the past reduction of water hyacinth population. Wilson et al. stated that the decline was mainly due to the introduction of weevils, while Williams et al. attributed the outcome largely to the wet and cloudy weather brought by the 1997/1998 El Niño effect. Wilson et al. used basically the remote sensing data on the coverage of water hyacinth on Lake Victoria. They pointed out that the major turning point of the population didn’t show up until 1999, which was one year after the El Niño effect had gone. Thus they affirmed that the biocontrol played a main role in the success. Meanwhile, Williams et al. used the same data set, but they viewed the water hyacinth population of different parts of the Lake separately. The figure in their paper demonstrated that during 1997-1998, the population went down in the Uganda and Tanzanian portions of the lake but up in the Winam Gulf in Kenya. They claimed that the above normal rainfall was responsible for the rise in Winam Gulf, which is a rather confined and sheltered region of the Lake.

While both papers provided adequate support to their points, the Williams et al. paper probably analyzed the data on a more reasonable basis, as such a water body as huge as Lake Victoria doesn’t seem suitable to be viewed as a whole. However, as argued by Wilson et al., the Williams et al. paper might lack substantiative link between low light levels and plant mortality.

In light of the MODIS satellite images, the fierce flood and rainfall swept nutrient-rich sediment into Lake Victoria, providing sufficient basis for a new outbreak of water hyacinth invasion. This fact reminds people that biocontrol is rather unstable when facing sudden megascale change in natural condition. As a result, biocontrol measures need to be deployed during a prolonged time period, especially in the cases of dealing with tenacious fast-growing invasive species. However, such continuous control may also bring the problem of importing another invasive species. Hence, biocontrol needed to be studied on a case-by-case basis according to local environmental conditions.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria.

http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake

Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic

Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P.

Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline

of water hyacinth on Lake Victoria was due to biological control by Neochetina spp.

Aquatic Botany 87:90-93.

Sep
13
Filed Under (SW3) by Shamaita Majumdar on 13-09-2010

The water hyacinth in Lake Victoria, Uganda, is affecting fishermen, clogging pathways, and destroying ecosystems. Wilson et al. 2007, and Williams et al. 2007, present their viewpoints on why the water hyacinth growth declined, crediting either the weevil biocontrol or El Nino, whose stormy weather can shift the plants and interfere with the ability of the plant to photosynthesize.

Wilson et al. 2007 credit weevils for water hyacinth reduction. They deny that future hyacinth re-proliferation is possible, saying the biocontrol is stable and that water hyacinth could never reinvade unless the “herbivore pressure [was] removed”(Wilson et al. 2007). Wilson et al. 2007 use a single graph comprised of data from satellite images to correlate time versus the area covered by water hyacinth, using this information to justify that the final decline in water hyacinth aligns with the duration necessary for weevils to work. The temporary drop in hyacinth coverage during El Nino is declared insignificant by Wilson et al. 2007.

Williams et al. 2007 make valid points against the Wilson et al. 2007 article, noting that the water bodies in question are large and varied; “to condense the system into a single graph is an over simplification of the spatial complexity” (Williams et al. 2007). Williams et al. 2007 break the data into three regions to compare the fluxes in water hyacinth growth simultaneously.  They concede that weevils contribute greatly to the decline of the water hyacinth, but stress that El Nino certainly accelerated the deterioration of the plants (Williams et al. 2007).

Williams et al. 2007 are more convincing because they pointedly refute the opposition’s points while maintaining a less radical viewpoint.  Williams et al. 2007 concedes that both El Nino and the biocontrol contributed to the decline, whereas Wilson et al. 2007 do not accept El Nino as a legitimate contributor. Williams et al. 2007 address Wilson et al. 2007’s proposal to measure water hyacinth’s photosynthetic efficiencies in situ, noting that they, in fact, did perform these shade-varying experiments. Williams et al. 2007 oppose Wilson et al. 2007, emphasizing that stability of the weevil is not guaranteed and regular monitoring will be necessary (Williams et al. 2007). In light of the MODIS satellite images which indicate that the lake has been reinvaded by the water hyacinth, it appears that not only was the Williams et al. 2007 article more convincing, but also accurate in assuming that the biocontrol alone is not effective (NASA Earth Observatory, 2007).

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Sep
12
Filed Under (SW3) by Hanna on 12-09-2010

Revised SW3:

A Chronic Epidemic

Water Hyacinth is gaining ground in Lake Victoria, and gaining it quickly. It forms thick mats on the surfaces of water. In doing so, it prevents light from entering the water, causing the death of indigenous plants and marine animals. Over the past few decades, scientists and researchers have set out to discover the characteristics of this invasive specie in order to address possible solutions to this growing problem. In doing so, water hyacinth has gained public awareness and press.

In Wilson et al. (2007) and Williams et al. (2007), a thorough debate took place in which supporting arguments were used to provide insight to the problem and potential solutions. In Wilson et al. (2007), biological control in the form of Neochetina eichhorniae is argued to be the best attempt to control the growing specie. Wilson argues that while the water hyacinth population grew after the El Niño season ended, this could actually be a result of the El Niño weather. It explains that waves and wind could carry the plant across bodies of water, and thereby actually help spread this invasive specie. It concludes that the only substantial evidence of maintaining and controlling the water hyacinth is through the continued presence of the weevil.

Williams et al. (2007) counters these claims in the belief that exclusively using biological control is not sufficient to manage this epidemic. Although the author agrees that “the introduction of weevils into Lake Victoria has had an impact on water hyacinth population” (Williams), he further attributes the sharp decline of this invasive species due to the prolonged wet and cloudy weather of 1997. During this time, the El Niño weather produced harsh conditions for plants to live in. The NASA Earth Observatory (2007) confirms this statement by stating that extremely heavy rainfalls would affect the use of biological control. During 1998, floods would cause plants to sink, taking with them weevil eggs, larvae and pupae. (Williams et al. 2007). As a result of the low light level from cloud coverage, which slowly reduces growth and reproduction rates, and the disruptive waves, water quality, humidity, and temperature brought on by this storm, water hyacinth had an accelerated decline in Lake Victoria at this time.

As discussed in Wilson and Williams, a heavy debate exists regarding the power and effectiveness of biological control in Lake Victoria. While Wilson argues that the decrease in water hyacinth can be attributed to biological control alone, Williams counters with other convincing evidence. After finding a solid correlation between rainfall, cloud coverage, and the presence of water hyacinth, Williams concludes that the steady decrease in this plant mass is caused by both the conditions produced by El Niño and the introduction of weevils. According to the evidence in these two literary journals, I am inclined to believe that the loss of water hyacinth can be credited to both the El Niño season and the presence of the Neochetina weevil. With compelling graphs and credible evidence, as well as strong counterarguments, Williams et al.’s solidifies the viewpoint that multiple measurements are needed to manage and control this chronic epidemic.

Reference:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87: 94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J.     Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87: 90-93.