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
20
Filed Under (SW3) by Michael Di Nunzio on 20-09-2010

Michael Di Nunzio

09/13/2010

Water hyacinth has posed a problem for Lake Victoria since first being reported there in 1989. The plant forms dense mats of vegetation that inhibit the movements of fishermen, block sunlight to native plants, and obstruct irrigation systems.  The invasive weeds can also deplete the water’s oxygen levels, suffocating the indigenous flora and fauna of the lake and in turn disrupting the local ecosystem. To control the hyacinth populations, invasive weevils (Neochetina spp.) were introduced with the intention of suppressing the noxious weed (Williams et al. 2007).

Using satellite image samples, Wilson et al. (2007) estimated the proliferation of water hyacinth over Lake Victoria and fluctuations in the plant’s presence over time, finally presenting their data in Aquatic Botany. However, Williams et al. (2007) warned with a rebutting article that this method of gathering data is oversimplified for such a complex environment. In spite of the dispute, both parties agreed that hyacinth levels dropped after the 1998 El Niño disturbed the lake. Following the initial decline came a steady rise until 1999 when hyacinth levels again began to decrease dramatically. From 2000 until 2002 hyacinth levels remained suppressed to under 5000 hectares of biomass over the lake’s entirety (Wilson et al. 2007).

Wilson et al. (2007) reasoned that the drop in 1999 was a result of the control weevils introduced in 1995 becoming effective after four years of relative dormancy. They also noted that the weevils control the weed by lowering its buoyancy and sinking it, and El Niño could have facilitated this process with wind and wave action. Because El Niño would inevitably blow some hyacinth into new areas, Wilson et al. (2007) suspected that local reports of hyacinth resurgences might have actually been false. Valid reports of resurgence may have resulted only if weevils died due to a lack of buoyant hyacinth, leaving the plant temporarily uncontrolled. According to Wilson et al. (2007), there was no substantive evidence to link low light levels with any of the withdrawals of hyacinth as Wilson et al. (2007) surmised.

Williams et al. (2007) placed less emphasis on the importance of the weevils in regards to water hyacinth control. Rather than biocontrol being a significant factor, they claimed El Niño more likely pulled hyacinth from the shoreline and destroyed it with wave action. This theory was both plausible and agreed seamlessly with the data showing a decline in 1998. Furthermore, the 2000 to 2002 nadir in hyacinth was thought to be a fleeting product of the weevil’s efficacy after 1999 and “suboptimal light” (Williams et al. 2007). Finally, Williams et al. (2007) pointed to the River Kagera as an ideal means of future resurgence, as hyacinth from this region is untainted with weevils and can float freely into the lake. This meant that there would be a delay before biomass control could take effect.

While Wilson et al. (2007) offered the more optimistic outlook on the data set, Williams et al. (2007) were unfortunately the most realistic. Williams et al. (2007) provided the most coherent argument, and aptly paralleled the situation in Lake Victoria with that of sub-tropical climates plagued by water hyacinth. They assumed that the lack of hyacinth is a part of a cyclic process involving a balance between weevils and weeds that will invariably lead to hyacinth resurgences. Wilson et al. (2007) tended to make unlikely excuses for all reported instances of resurgence, rather than offering any real insight into the possible validity of their reasoning. The satellite images from MODIS vindicate the argument of Williams et al. (2007), as resurgence obviously took place by 2006 (NASA 2007). Thus the relationship between adequate light, the presence of weevils, and the predominance of hyacinth must be a continued subject of study at Lake Victoria if definite conclusions about the hyacinth resurgence cycle are to be drawn. However, Williams et al (2007) seems to have lead us in the right general direction.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 12 Sep 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

Sep
14
Filed Under (SW3) by Michael Di Nunzio on 14-09-2010

Michael Di Nunzio

09/13/2010

Water hyacinth has posed a problem for Lake Victoria since first being reported there in 1989. The plant forms dense mats of vegetation that inhibit the movements of fishermen, block sunlight to native plants, and obstruct irrigation systems.  The invasive weeds can also deplete the water’s oxygen levels, suffocating the indigenous flora and fauna of the lake and in turn disrupting the local ecosystem. To control the hyacinth populations, invasive weevils (Neochetina spp.) were introduced with the intention of suppressing the noxious weed.

Using satellite image samples, Wilson et al. (2007) estimated the proliferation of water hyacinth over Lake Victoria and fluctuations in the plant’s presence over time. However, Williams et al. (2007) warns that this method of gathering data is oversimplified for such a complex environment. Regardless, the results indicated that hyacinth levels dropped after the 1998 El Niño disturbed the lake. Following the initial drop in 1998 came a steady rise until 1999 when hyacinth levels again began to decline dramatically. Hyacinth levels stayed at close to zero from 2000 until 2002.

Wilson et al. (2007) reasoned that the drop in 1999 was a result of the control weevils introduced in 1995 becoming effective after four years. They also note that the weevils used indirectly lower plant buoyancy as a means of sinking and controlling the weed, and that wind and wave action from El Niño could have facilitated this process. Because El Niño would inevitably blow some hyacinth into new areas, Wilson et al. (2007) suspected that local reports of hyacinth resurgences might have actually been false. Valid reports of resurgence may have resulted if weevils died due to a lack of buoyant hyacinth leaving the plant temporarily uncontrolled. According to Wilson et al. (2007), there is no substantive evidence to link low light levels with any of the withdrawals of hyacinth.

Williams et al. (2007) places less emphasis on the importance of the weevils in regards to water hyacinth control. Rather than weevils controlling the plants, El Niño more likely pulled hyacinth from the shoreline along with native plants and destroyed them in the lake with wave action. This would account for the decline in 1998. Furthermore, the current nadir in hyacinth is thought to be a fleeting byproduct of the weevils efficacy after 1999 and “suboptimal light.” Williams et al. (2007) points to the River Kagera as a source for resurgence, as hyacinth from this region is untainted with weevils and can float freely into the lake. This means that there is a delay before the biomass control can take effect.

While Wilson et al. (2007) offers the more optimistic outlook on the data set, Williams et al. (2007) is unfortunately the most realistic. Williams et al. (2007) provides the most coherent argument, and reasonably parallels the situation in Lake Victoria with that of sub-tropical climates plagued by water hyacinth. They assume that the current lack of hyacinth is a part of a cyclic process involving a balance between weevils and weeds that will invariably lead to hyacinth resurgences. Wilson et al. (2007) seems to make convenient excuses for all reported instances of resurgence, rather than offering any real insight into their possible validity. The satellite images from MODIS vindicate the argument of Williams et. Al (2007), as resurgence obviously took place by 2006. Thus the relationship between adequate light, the presence of weevils, and the predominance of hyacinth must be a continued subject of study at Lake Victoria if definite conclusions about the hyacinth resurgence cycle are to be drawn.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nas/IOTD/view.php?id=7426. Viewed 12 Sep 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

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.

Sep
13
Filed Under (SW3) by Sean Dickey on 13-09-2010
Ever since the 1980s, the water hyacinth of Lake Victoria have been a huge menace to inhabitants of the surrounding region. Problems stemming from the water hyacinth include, sub-par water quality, impossible navigation through the lake, rotting vegetation, and a resulting environment conducive to parasitic diseases such as schistosomiasis. As a way to combat the takeover of Lake Victoria by the water hyacinth, Dr. James Ogwang, a biocontrol entomologist, deployed the South American weevil, a natural enemy of the water hyacinth, to quell the overwhelming numbers of the aquatic invasive plant.
About five years after the weevil was introduced, there was a huge decrease in the amount of water hyacinth in Lake Victoria. However, there is much debate as to what phenomenon actually triggered this reduction. At the same time the weevil population was feeding on the water hyacinth, the global weather phenomenon El Niño occured as well. The shifted weather patterns redistributed some of the water hyacinth throughout the lake and damaged them due to stormy weather (Wilson et al. 2007). The theory supported by Wilson et al is that El Niño had an effect on the water hyacinth populations, but it wasn’t as significant as the weevil. They offer the assertion that the only way the water hyacinth could have a population resurgence is if the weevil populations were disrupted (Wilson et al. 2007). In Williams et al, they offer the theory that although the weevil population had an effect on the water hyacinth, the lake-encompassing reduction of the water hyacinth is mostly due to El Nino (Williams et al. 2007).
Both views on what happened to Lake Victoria were very well backed by evidence, but the theory supported by Wilson et al had a serious hole, the water hyacinth made a resurgence in 2006, after the scientific article had already been written(NASA Earth Observatory 2007). The article written by Wilson et al specifically claimed that the weevil populations would have to be disturbed in order for the water hyacinth population to significantly increased. However, when the water hyacinth began to cover the lake, nothing of significance happened to destroy the weevil populations. This ultimately suggests that the weather of El Niño had the greater effect on the reduction of water hyacinth in Lake Victoria.
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.