Oct
31
Filed Under (SW10) by Sean Dickey on 31-10-2010

The use of biocontrol agents in the management of invasive water hyacinth hasn’t always been successful. In South Africa, the two weevils, Neochetina eichhorniae and N. bruchi, aren’t extensively as the growth rate of the aquatic plant is too fast for them. The eutrophication of lakes and other water bodies allows the water hyacinth to produce leaves faster than the weevils can eat them.

In a study conducted by Jadhav A., Hill, M., and Byrne, M. of University of the Witwatersrand and Rhodes University, they explored the potential effect of applying non-lethal doses of glyphosate on the plant. By using non-lethal doses, the researchers hoped they could slow the growth of the plant to levels that could be regulated by biocontrol agents. In order to test this theory, they designed an experiment in which small samples of water hyacinth were placed into tubs while treatments of herbicide and weevils were applied over an eight week period. The experiment was successful as no organisms outside water hyacinth were harmed in the 0.8 % glyphosate dose. As predicted, feeding levels by the weevils increased as well. In the future, more research needs to be conducted in the field to see if the same results can be reproduced.

Biological Control 47, 154-158 (2008)

Oct
13
Filed Under (SW7) by Cecile Diaz on 13-10-2010

Larson confronted the issue of using militaristic language and metaphors in scientific articles about invasive species. Larson argues that although using militaristic metaphors may seem like a good way to raise awareness, both in a public way and in a scientific manner, it is actually counter-effective because it causes confusion about the problem and what we should do about it. Larson identifies three problems with using militaristic language: first, it causes people to consider invasive species inaccurately; second, the language creates “social misunderstanding, charges of xenophobia, and loss of scientific credibility; and third, the language is ineffective in the long-term for conservation because the species are consistently related to wars and fighting.

Looking back on previous WordPress posts by my classmates and myself, I came across a post of my own that had a militaristic term in the title: “El Nino vs Weevils: which is the conqueror of water hyacinth?” In incorporated the word “conqueror” because I wanted a strong word that would convey the idea of vanquishing the hated water hyacinth from Lake Victoria. However, upon reading Larson’s article, I found that this term is not only contextually incorrect, but actually detrimental the argument I based my opinions on. The water hyacinth isn’t an enemy that needs to be conquered, it’s just an invasive species that is extremely problematic and needs to be prevented. Acceptance of the issue is crucial so as to prevent issues like this in the future, and we need to accept that we might not be able to eradicate the water hyacinth from Lake Victoria. Larson would advise the public to understand that water hyacinth wouldn’t have entered Lake Victoria without human interference, and since we can’t look back on our mistakes, we just need to push forward and try and prevent further infestation.

The use of militaristic language is overall negative because it implies that there is a war, which requires two sides, and that we will eventually win because humans are the good forces and the invasive species are the bad forces. I agree with Larson when he says we are not fighting the species, we are just fighting what we ourselves created, which is never a winning situation. Additionally, when we relate invasive species to wars, this just dilutes the meaning of warfare and allows further abuse of the word and relative language. It’s unacceptable to compare invasive species to terrorist attacks, or overseas firefights, because ultimately methods can be implemented to reduce effects of invasive species, whereas wars and their consequences are permanent. Larson argues that instead of using militaristic language, which is in fact counterproductive, scientists should start creating alternate means of promoting conservation while still being firm. We should direct the meaning and understand of invasive species not towards opposition, but towards prevention and control.

References:

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

Diaz, Cecile. 2010. El Nino vs Weevils: which is the conqueror of water hyacinth? http://sites.duke.edu/writing20_12_f2010/2010/09/13/analysis-of-fierce-debate-of-water-hyacinth-on-lake-victoria/

Photo taken from Geography: Staffordshire Learning Net

Oct
12
Filed Under (SW7) by Dan Tully on 12-10-2010

Larson (2005) describes an argument that the use of aggressive or militaristic language is not an effective way to combat invasive species.  Larson (2005) argues that the militaristic writing styles encourages the reader to want to get involved with the effort to slow the spread of invasive species.  However, this usually leaves the reader misinformed or entirely uniformed about the actual situation, which can lead to rash, ineffective, and or harmful, actions being made.

In my own blog posts I have used militaristic language.  When describing the issue of the water hyacinth on Lake Victoria  I used lines such as, “the water hyacinth has been extremely destructive to both the species of Lake Victoria and the humans who depend upon the lake for food and water,” and later on, describing which scientific study I believe is more correct, I continue to use militaristic language, “the weevil is now the dominant force driving down the water hyacinth population.  Williams et al (2007) fails to give reasoning for why, even after the 1998 El Nino, the water hyacinth population has not experienced the same expansive growth rate that it did prior to El Nino.”  Specific key militaristic phrases in these quotes are, extremely destructive, dominant force driving down, and expansive growth rate.  I do agree with Larson (2005) that language such as the examples above does simplify the gravity of the situation by showing only part of the picture.  And for any argument to be successful, both sides of the issue must be represented.

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

Sep
27
Filed Under (SW5) by Sean Dickey on 27-09-2010

Although the highly invasive water hyacinth was introduced into Florida over 30 years ago, the aquatic plant hasn’t been nearly as successful as it has been in other places such as Lake Victoria, South Africa. Despite this, Florida’s weather and conditions are optimal for sufficient growth of water hyacinth. The warm climate, high nutrient and light environment is very conducive to water hyacinth growth. Researchers Volin and Soti from the University of Connecticut and Florida Atlantic University sought to test various nutrient and herbivory levels  versus water hyacinth growth to see if the specific amount of nutrients and plant removal found in Florida had a negative impact on the water hyacinth. Soti and Volin found that water hyacinth are able to survive under low amounts of plant removal no matter the nutrient level. This suggests the most effective method of removal of the plant is a high level of herbivory. This research gives great insight into future control of the highly invasive plant.

Biological Control Vol. 54 Issue:1 35-40 July 2010

Sep
21
Filed Under (SW3, Uncategorized) by Albert Chen on 21-09-2010

The Water Hyacinth is an invasive species that has proliferated since its introduction to Lake Victoria in the 1980’s. The lack of natural predators has allowed the plant to form dense mats over the lake, stagnating surface waters.  Lentic water provides breeding grounds for mosquitos and other disease causing organisms. The plant also robs sunlight, nutrients, and oxygen from the native species, hinders boating, and interrupts subsistence fishing. One of the more recent cleanup efforts involves the use of Neochetina, a weevil that predates on the Water Hyacinth. This form of biocontrol’s degree of effectiveness is a subject being debated.

El Nino weather patterns in 1997/1998 Lake Victoria were stormy, and water hyacinth numbers dipped around same time. Wilson et al. (2007) concluded that the incidental weather was only supplemental to the pressure imposed by the weevils. Low sunlight levels, they argue, present little trouble to the flourishing hyacinths in West Africa and Papua New Guinea and is not a major threat to the plants’ survival.  The study also points out that Lake Victoria’s time frame between weevil introduction and hyacinth decline is consistent with the maximum four years shown in other countries. Being the only control method implemented across the whole lake, weevil biocontrol is likely the main source of the drop. Wilson et al. however acknowledges that the wind and wave action can be major stressors to the perforated, weevil-ravaged plants.

Williams et al. (2007) address the arguments presented by Wilson et al. (2007) by clarifying that though poor lighting may not kill the plants, it is a stressor that compounds with other weather related factors such as water level, wave action, water quality, temperature and humidity. The study also calls attention to the 1998 “crash” that came prior to the larger hyacinth drop. Williams et al. (2007) believe that early deterioration of plant quality led to instability and weevil decline; plants sink, “taking with them weevil eggs, larvae, and pupae.” Williams et al. (2007) agrees that weevils are integral to the reduction of the water hyacinth, but notes that weevil densities remained low up to 2002 and likely did not play the largest role in hyacinth damage.

The authors of both studies seek to better monitor the hyacinth and weevil populations.

Hyacinth populations have rebounded since the two studies were written; nutrient laden runoff is suspected (NASA Earth Observatory, 2007).

I think the studies complement each other very well because each presents new scenarios and variables to be considered. I believe Williams et al. (2007) explanation regarding unstable bug populations is correct because weevils are very weak swimmers and heavily dependent on their hosts.

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 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 Cecile Diaz on 13-09-2010

Scholars debate the main factor of the significant decrease of water hyacinth on Lake Victoria around 1999-2000 in Wilson et al. (2007) and Williams et al. (2007). First, Wilson et al. (2007) replies to a previously published article by Williams et al. (2005) which claims that although weevils played a role in the eventual decrease of water hyacinth on Lake Victoria, the invasive species’ population was ultimately and predominately the result of the 1997/1998 El Nino. Williams et al. (2005) cites the condition of “low light availability” from El Nino and its subsequent effect on water hyacinth’s growth as the main contributor to the weed’s destruction.

Wilson et al. (2007) counters the referenced article by stating first, Neochetina bruchi and Neochetina eichhorniae (collectively Neochetina spp.) were the primary destructive agents to water hyacinth; second, El Nino caused waves and strong currents on Lake Victoria which dispersed its water hyacinth and made the weed easier to destroy by weevils; and third, water hyacinth will not reemerge in Lake Victoria unless its Neochetina spp. populations are disturbed. The authors reevaluated the light conditions around the time of El Nino, but found that by mid-1998, water hyacinth was already rebounding on Lake Victoria. Wilson et al. (2007) acknowledged that weevils took nearly four years to take effect against the invasive species in 1999 (weevils were released into the lake in 1994), but this timetable was expected and is congruent with weevil versus water hyacinth time frames from other countries with similar climates.

Lastly, in Williams et al. (2007)’s rebuttal to Wilson et al. (2007), the authors restate their aforementioned claim that weevils contributed to the reduction of water hyacinth around 1999-2000, but the invasive species would certainly still be growing strong in the absence of the 1997/1998 El Nino. Williams et al. (2007) believe Wilson et al (2007)’s arguments are oversimplified and thus erroneous because Lake Victoria is simply too vast to be considered on an individual graph of experimental results. Williams et al. (2007) maintains the diminution of water hyacinth was a result of El Nino’s flooding because it transpired “synchronously…during the second quarter of 1998”. The authors claim the hyacinth’s first reduction occurred because the floodwaters dislodged the mats that held the weed to the lake floor, and the hyacinth simply washed away into the lake. While Wilson et al. (2007) stated that Williams et al. (2005) believed low light levels caused the reduction, Williams et al. (2007) stressed that the plant mortality was due to prolonged low light, not intermittent glares, which then caused minimal growth in the plants and weak mats.

Ultimately, I believe Wilson et al. (2007) had the soundest argument, which claimed that weevils played the most significant role in reducing the population of water hyacinth on Lake Victoria. While both articles acknowledged the “lesser” cause (whether it was weevils or the effects of El Nino), I felt that Williams et al. (2007) was especially narrow-minded and barely accredited weevils as a destructive force to weevils, when they were clearly a great contributor to the hyacinth’s periodical demise. However, the fact that the water hyacinth continues to make reappearances on Lake Victoria suggests tha solely biocontrol as a method of eradication is insufficient and ultimately non-cost effective. There needs to be a more radical and long-lasting approach to ridding Lake Victoria from the ruthless water hyacinth.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 10 Sept 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 Josh McGrath on 13-09-2010

The largest lake in Africa, Lake Victora, is cut up by 3 nations, so naturally it would be difficult to completely keep foreign invaders out. Since 1989, the water hyacinth has plagued Lake Victoria and its people. It has caused issues with the transport routes through the lake, the fishing conditions, and biodiversity in the lake. The people who had once depended on the lake for food, water, and livelyhood were affected drastically. Measures were obviously taken to try and get rid of the invasive plant, particularly the herbivorous Neochetina, but many speculate as to whether it was the weevils or the seasonal El Niño.

The debate got particularly sparked by the Wilson et al. (2007) article and the opposing Williams et al. (2007) response. Wilson et al. (2007) article insists that it was primarily the weevil that caused the demise of the water hyacinth. While it acknowledges that the El Niño of 1997/98 may have helped in the decline(as there was an initial decline), it also clearly shows in its graph that the large decline in plant population occurred a year after the El Niño. The article says that the weevils deserved whole responsibility for the biocontrol that occurred.

Williams et al. (2007), on the other hand, gives credit to both the introduction of the weevil and the El Niño. It claims that there is no way the weevil could successfully fight off the water hyacinth without the help of such a large storm. The reduction in sun light, changes in temperature, and water levels, among other effects caused by the storm, aided the weevil in its prolonged attack against the plant. The article does, however, explain that it will ultimately be the weevil that keeps the hyacinth from returning.

Recent satellite imagery disagrees with the Williams et al. (2007) article and especially with Wilson et al. (2007). It shows clearly that the water hyacinth not only returned, but even spread despite the presence of the weevil. While both articles were inevitably wrong, it is clear that one was more correct than the other. The fact that the Wilson et al. (2007) article refuses to admit that the El Niño even really played a significant role in the demise of the hyacinth, automatically makes the Williams et al. (2007) more correct. The willingness to be open to multiple contributing factors and ideas, proved to be the better route.

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 Reinsvold on 13-09-2010

The water hyacinth plant is an extremely aggressive aquatic plant.  In 1989 it was spotted in Lake Victoria, the largest lake in Africa.  The plant took over tens of thousands of hectares.  In the past decade there have been multiple efforts to combat the water hyacinth invasion.  In 1995 weevils were introduced as a method of biocontrol,  since they have an appetite for the water hyacinth and not local plants.  Wilson et al.(2007) suggest that the weevil was the primary source of decline during 1998 and early 1999.  However, between 1998 and 1999, the largest El Nino event of the century was recorded.  Wilson et al.(2007) admit that the environmental impact of El Nino contributed to the decline of the water hyacinth as well  but they maintain that the weevils were the primary cause for the decrease in the water hyacinth biomass.  The reason the weevils did not have a major effect before 1998 was because it took them three years to spread and multiply.

Williams et al.(2007) make the flip side of this debate over whether the weevil or El Nino was primarily responsible for the decline of water hyacinth in 1998-1999.  Williams et al.(2007)claim that while the weevils aided the decline of water hyacinth, it was El Nino that accounted for most of the decline.    Lake Victoria is massive and subsequently it is difficult to describe it as a single environment.  While the weevil was able to affect much of the water hyacinth once it expanded,  El Nino was able to impact the entirety of the water hyacinth invasion.  The low amounts of sunlight combined with heavy rain decimated the plant.  Williams et al.(2007) make a stronger case of El Nino.  They make use of multiple data points while Wilson et al.(2007) use only one.

Since 2007, however, the water hyacinth in Lake Victoria has been increasing.  The evidence is provided by recent NASA satellite images.  The resurgence is likely caused by two primary effects.  The first one being that the decline in water hyacinth also decreased the weevil population.  The weevils declined as their primary food source decreased.  It curbed the weevil population boom.  The second reason is likely the lack of El Nino.  The El Nino event had a profound impact on the water hyacinth.  Without it, the plant was able to make a recovery.  It is interesting to see how the water hyacinth population changes over the coming years.

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 Lindsay Gaskins on 13-09-2010

Water Hyacinth

The water hyacinth has been the subject of both much concern and debate over the past years.  It’s dramatic takeover of Lake Victoria in Uganda has sparked a heated discussion on why the invader suddenly receded, though it later came back.  The opposing views were in expressed in Wilson et al, arguing that weevils should be given the most credit for the reduction of the water hyacinth, whereas Williams et. al presented the argument that El Niño should be given the credit.

The Wilson et al. paper presents a strong argument, saying that the weevils introduction to Lake Victoria was the main reason for the water hyacinth’s decline.  Though they acknowledge that El Niño may have had a slight effect on the water hyacinth population, the light levels that got through the cloudy weather as a result of the altered climate pattern would’ve been enough to keep the water hyacinth population alive and growing, so the answer to the question of why the water hyacinth declined muse lie in the biocontrol, or the weevils.  Williams et al. presents essentially the opposite argument,  saying that El Niño’s cloud pattern would’ve blocked out light for the water hyacinth, therefore making it hard from them to photosynthesize and expand throughout the lake.  To back their argument, they cited that this wet and cloudy weather had a detrimental effect upon vegetation throughout other parts of Africa as well, and that the weevils may had a helping hand in the decline, but were in the end, of nominal effect in the larger scheme of things.

I think that Wilson et al.’s argument in favor of the biocontrol makes the most sense, given the dramatic reduction of water hyacinth population after the introduction of the weevils, and the sustained decline even after the passing of El Niño. Though the light levels made have adversely effected the population of the water hyacinth, the light levels despite the cloudy weather wouldn’t have stopped their growth and caused the population reduction.  Though, as MODIS images revealed, the water hyacinth has returned, it just reminds us that when using biocontrol, that constant monitoring is required, and problems with invasive species will be something that our society will have to learn to cope with for many years to come.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 13 Sept 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.

Photo from here.