In 1989, the invasive species known as water hyacinth was first reported on Lake Victoria. In 1998, an outbreak of the plant covered as much as 17,231 hectares (NASA Earth Observatory, 2007) of the lake. Weevils, insects that eat the plant, were introduced into the lake in 1995 (Williams et al., 2007) and by 2000, an almost complete eradication of water hyacinth was observed in Lake Victoria (NASA Earth Observatory, 2007). Scientists are debating over the cause of the decreasing population of the water hyacinth. The question is: Was the decrease in water hyacinth on Lake Victoria caused by the introduction of weevils or a weather phenomenon El Niño?
Wilson et al. (2007) argues that the decline in water hyacinth on Lake Victoria was due to biological control by Neochetina weevils. They cite how the reduction of water hyacinth occurred four years after the introduction of the weevils, and how this time frame has also been observed in other parts of the world where weevils have been introduced to reduce water hyacinth populations. Wilson et al. (2007) shows that only a few years after the initial introduction of the Neochetina weevils the water hyacinth populations crashed.
Contrastingly, Williams et al. (2007) contributes the majority of the water hyacinth decrease to the natural weather phenomenon El Niño. Williams et al. (2007) claim that the low light conditions caused by El Niño “will reduce growth and reproduction rates and relatively increase the effect of other debilitating influences such as other weather related factors, e.g. water level, wave action, water quality, temperature and humidity as well as weevil herbivory and phytopathogenic attack”.
The low populations of water hyacinth Lake Victoria did not last. By December of 2007 the water hyacinth was back in the lake (NASA Earth Observatory, 2007). NASA determined this using a satellite Moderate Resolution Imaging Spectroradiometer (MODIS). NASA contributes the rise in water hyacinth populations to “unusually heavy rains that flooded the rivers … and swept agricultural run-off and nutrient rich sediment into the water”. This new data may mean that the biocontrol in Lake Victoria was ineffective.
I believe that the Neochetina weevils undoubtedly contributed to the initial drop in the water hyacinth (Wilson et al., 2007), however, Wilson et al. (2007) presented a more convincing argument that the majority of the decline in water hyacinth was caused by El Niño. This is apparent when looking at the graphs presented in Wilson et al. (2007), they clearly show that there is a more direct connection to the decline in water hyacinth with El Niño than there is with the introduction of weevils. The problem of water hyacinth needs to be solved and hopefully scientists can find affective methods to keep the growth of the plant controled.
References:
NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 12 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.
In 1989, the water hyacinth infestation of Lake Victoria began (Williams et al. 2007). During the 1990s, this plant invader quickly spread to cover up to 20,000 hectares or ~77 square miles of water in the area. These thick mats of plant covering most of the lake were a menace to the local economy, living conditions, and ecosystem. (NASA Earth Observatory 2007)
This could not continue, so starting in December 1995, the hyacinth-eating weevil was introduced to the lake as a form of bio-control (Williams et al. 2007). Later, from 1997-1998, El Niño, a weather pattern inducing stormy weather, occurred (Wilson et al. 2007). By 2000, the water hyacinth population was 97.5% depleted (NASA Earth Observatory 2007). The current debate is over which factor was the primary one in reducing the hyacinth infestation: human bio-control, or nature’s El Niño.
John R. U. Wilson and others argue that the introduced weevil was crucial to the water hyacinth “population crash.” These scientists state that the weevil larvae tunnels caused unseen internal damage to the plants. This enabled the mats of hyacinth to easily be uprooted and dispersed across the lake. Another arguments brought up is that even after the storm, the plants scattered across the lake did not re-surge in population. Wilson and his colleagues are firm believers that as long as the weevil is not disrupted, the water hyacinth will be suppressed.
On the other hand, Adrian E. Williams and others respond that though weevils had a negative effect on the hyacinth, the depopulation was mainly due to the El Niño storms of 1997-1998. These scientists waive the arguments of Wilson’s team saying that the biological processes of weevil larvae can not be generalized for a lake as large and complex as Lake Victoria.
With the return of the water hyacinth in the December 2006 (NASA Earth Observatory 2007), it appears that Williams and her colleagues are justified in their arguments. I agree with them that bio-control is limited in its effectiveness in reducing invasive species when compared to the dynamic forces of nature, which could easily override any human efforts to regulate or control ecosystems. Yes, the weevil played a part as intended, but from introductory statistics courses, “correlation does not imply causation” (Information Works 2009). The destruction the Water Hyacinth should not be attributed to human bio-control when there are more significant forces at work.
References:
Information Works: Rhode Island Public Schools. 2009. Correlation Does Not Imply Causation http://www.infoworks.ride.uri.edu/1999/techbrief/techbrief_8.htm>. Viewed 12 Sept 2010.
NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 12 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.
Water hyacinth entered the Lake Victoria region late in the year 1989. This South American plant quickly spread throughout the lake and covered a large percentage of the lake’s surface in only a few years time. It soon became clear that water hyacinth was an invasive species, since it was the a major reason why several domestic plants and animals perished. Surprisingly though, beginning in 1997, the water hyacinth population decreased significantly. The reason to why this phenomenon happened has been debated by scientists.
Wilson et al. claims in their research paper that this random decrease is directly related to a biocontrol method. The method, introduced in 1995, consisted on the importation of a weevil called Neochetina bruchi into the Lake Victoria area. The weevil eats away at the water hyacinth’s leaves and causes bacteria to enter into the root system through cracks (Wilson et al. 2007). Studies show that the amount of time before the weevil bio-control became effective is consistent with the infestation of this weevil in other parts of the world (Wilson et al. 2007). Wilson et al.’s paper is adamant that bio-control is the sole cause of the decrease of the water hyacinth.
Williams et al. attributes some responsibility to biocontrol for the decrease of the water hyacinth population, but claims that weather patterns should deserve most of the credit. The natural climatic event called El Nino occurred in the year 1997 and created new weather conditions for the Lake Victoria area. Flooding occurred throughout east Africa, and the water level of Lake Victoria rose by 1.7 meters (Williams et al. 2007). This water level rise caused the water hyacinth to be dislodged and to break away from its position in the water base (Williams et al. 2007). Williams et al. believes that this dissociation caused the water hyacinth to eventually perish and die out.
In my opinion, Wilson et al.’s argument has a stronger position on the debate. After an initial decrease of the amount of water hyancinth following El Nino, the population actually increased for a year, and then eventually decreased into almost non-existence (Wilson et al. 2007). With this data, it seems clear that the weevil was the major reason for the downward trend. Unfortunately, the downward trend did not last. The water hyacinth population did not disappear completely. Late December 2006, MODIS satellite images illustrated an obvious increase of the water hyacinth population. The weed was found to cover a large portion of Lake Victoria once again (NASA Earth Observatory 2007). From this new information, it appears that bio-control can be effective at first, but it is not a solution to the problem. Bio-control is only treatment; Lake Victoria needs a cure.
References:
NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 11 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 biologial control? A Reply. Aquatic Botany 87: 94-96.
Wilson, J. R. U., O. Anjuonu, T. D. Center, M. P. Hill, M. H. 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.
Water hyacinth first invaded Africa’s Lake Victoria in 1989, quickly spreading and forming thick mats around the shoreline. In an attempt to control it, a weevil, Neochetina spp. was introduced in 1995. In 1997 and 1998 the water hyacinth began to decrease drastically, seeming to clearly indicate a success for the weevil. But around this same time, El Nino weather patterns occurred over the Pacific Ocean with repercussions that could be felt over Lake Victoria. From these facts has sprung a debate over whether the decline of the water hyacinth was due to the weevils or the El Nino-related weather.
The main point of disagreement between the two opinions about water hyacinth’s decline is the meaning of the time between the introduction of the Neochetina spp. and the noticeable decline in water hyacinth. Wilson et al. (2007) states that although the El Nino-associated weather, namely increased wind and wave patterns on the lake and decreased light availability, added further stress for the water hyacinth to deal with, they were just a mercy stroke for already doomed plants that were fatally damaged by the weevil. They believe that the time difference was a normal occurrence for a biocontrol agent, no more than a “lag time” while it became established and that it was coincidence that it really began to take effect at the same time as the El Nino event. Williams et al. (2007) on the other hand assert that although the weevils did their part, the decline of water hyacinth on Lake Victoria would not have occurred without the timely El Nino event. They say that while the weevil did some damage to the water hyacinth, it would not have declined as it did without the El Nino weather patterns.
Both articles present valid arguments and it seems clear that the both the weevils and the El Nino weather had a part in the decline of the water hyacinth. In light of the new satellite images from NASA’s Earth Observatory, depicting a resurgence of water hyacinth, it is clear that the biocontrol was a short term solution. Williams et al. provides the best explanation for this resurgence of water hyacinth: “unstable host populations may well lead to unstable controlling herbivore populations,” that is, once the water hyacinth had declined by a significant amount, the weevils lost their food source and their population dropped too low to effectively control the invasive species.
References:
NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 11 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 biologial control? A Reply. Aquatic Botany 87: 94-96.
Wilson, J. R. U., O. Anjuonu, T. D. Center, M. P. Hill, M. H. 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.
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.
Conflicting Opinions on Water Hyacinth Invasion Control in Lake Victoria
In 1879 Water Hyacinth was introduced to Lake Victoria NASA Earth Observatory (2007). This invasive species took root over the next one hundred years and wreaked havoc by blocking oxygen to native species, impeding fishing boats and spreading disease. To control the Water Hyacinth, biocontrol in the form of the Neochitina weevil was implemented. An El Nino that occurred between 1997 and 1998 also played a role in Water Hyacinth reduction Wilson et. al. (2007). In 2007 two scholarly papers were published that offer differing opinions on the Water Hyacinth control issue.
The first paper, entitled “The Decline of Water Hyacinth on Lake Victoria Was Due to Biological Control” argues that Neochitina weevils were the primary reason for reduced Water Hyacinth levels between 1998 and 2007. Wilson et. al. (2007) report that weevils were reducing Water Hyacinth at a steady rate and they believe that the El Nino confused data on the Water Hyacinth issue. During the storm matts of Water Hyacinth broke loose and drifted to other areas of the lake, and El Nino kicked up sediment with Water Hyacinth seeds in it that started new Water Hyacinth growth, which lead to unusual data. Despite the uneven Water Hyacinth growth following the storm, Wilson et. al. (2007) believe that the Water Hyacinth will continue to be controlled by the weevils.
The second paper, “Water Hyacinth Decline Across Lake Victoria- Was it Caused by Climatic Perturbation or Biological Control? A Reply” is a response to the findings of Wilson et. al. (2007). Williams et. al. (2007) are concerned that a resurgence of Water Hyacinth may occur. They believe that lack of light and harsh weather conditions during El Nino reduced the growth rate and health of the Water Hyacinth. Williams et. al. (2007) therefore believe that El Nino, and not just the weevils, is responsible for the recent reductions in Water Hyacinth growth. Williams et. al. (2007) also believe that when Water Hyacinth levels are reduced they will have a negative impact on weevil health thus leading to a long term resurgence in Water Hyacinth growth.
Recently data from NASA Earth Observatory (2007) has shown that Water Hyacinth growth has increased. NASA Earth Observatory (2007) believe that stormy weather in December of 2006 caused increased water levels and released nutrient rich sediment into Lake Victoria. I believe that Water Hyacinth is going to be an ongoing problem in Lake Victoria and while both storms and biocontrol have reduced its growth, the most important thing is to keep monitoring Water Hyacinth growth and researching other methods that can reduce it’s growth. The recent resurgence shows that El Nino did have a role in reducing the Water Hyacinth growth, so it will be difficult to control the Water Hyacinth in the future with weevils alone.
References:
NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 12 Sept 2010.
William, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline accross Lake Victoria- Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94096.
Wilson, J. R. U., O. Ajounu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenshwander, S. E. 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.
Eichhornia crassipes, commonly known as water hyacinth, is an aquatic plant that has lily-pad-shaped leaves and beautiful lavender flowers. Despite its aesthetic beauty, water hyacinth is an extremely invasive species. It originated in the tropics of South America and has spread to inhabit every continent except Europe. In Lake Victoria, for instance, water hyacinth is so abundant that it blocks the passage of fisherman to fishing waters, and blocks pipes necessary to bring drinking water into cities and villages. In addition, since the plant covers the surface of the water, it inhibits the sun from reaching native species deeper down, causing those plants and fish to suffer (NASA Earth Observatory, 2007).
Since its first appearance on the lake in 1989, scientists have been trying to find ways to eliminate this plant. One of the mechanisms that they employed is biological control, or introducing a biological species to help reduce the invasive specie. To help exterminate the water hyacinth problem in Lake Victoria, Neochetina, or weevils, were introduced in 1995. Since these animals have an appetite for water hyacinth but don’t affect native species, Wilson et al. published an article in Aquatic Botany in which they argue that this method was extremely effective in reducing the abundance of the invasive plant on Lake Victoria (Wilson et al., 2007). However, in 1997-1998 there was also an occurrence of El Niño in the area which caused weather patterns that were detrimental to water hyacinths. Therefore, Williams et al. published another article in the same journal in which they attributed the reduction of the invasive species to this event, and not to biological control. They argue that the prolonged lack of light caused by El Niño reduced the growth and reproduction rates of the plant, making it more susceptible to other factors such as change in water levels and wave action brought about by El Niño (Williams et al., 2007). Although El Niño was responsible for the water hyacinth reduction that happened immediately after El Niño occurred, the weevils were responsible for the major reductions of the plant which didn’t occur until 1999-2000.
Although their opinions differ on what caused the decline of water hyacinth in 1999-2000, both Williams and Wilson agree that further research on the issue is necessary (Williams et al., 2007). This is even more crucial now that there has been a resurgence of water hyacinth in the lake (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.
In Lake Victoria, an invasive species is covering the water’s surface with green mats and blocking plants underneath it from direct sunlight, causing their death and many other related problems such as decrease in water quality and spread of waterborne disease. This species, the water hyacinth, has been a great puzzle for scientists. The original method of biological control, weevils (or Neochetina spp.), were introduced to reduce the water hyacinth population in 1995. A sharp decline of water hyacinth in 1998 and 1999 and again in 2000 is attributed to the weevils’ destruction by Wilson et al. (2007). However, according to a rebuttal article from Williams et al. (2007), the weather patterns brought by El Niño in 1997 and 1998 were mostly responsible for the water hyacinth’s decline.
According to Wilson et al. (2007), it is apparent that weevils caused the decline of the water hyacinth population because after their introduction, they normally take about three to four years to act, consistent with their introduction in 1995 and the decline in 1998 and 1999. They also claim that the resurgence shown on their graph of Lake Victoria hyacinth levels in 2000 occurred simultaneously with a low weevil population.
In contrast, Williams et al. (2007) argue against the claims made in Wilson et al. (2007). An interesting fact cited by Williams et al. states that El Niño caused a 1.70 meter rise in Lake Victoria’s water levels, which led to stable shoreline stands of water hyacinth washing into the lake. This compelling evidence, as well as individualized graphs for each region of the lake and explanations of how low light levels from El Niño’s stormy effects combined with other factors, including biological control using weevils, reduced water hyacinth populations, solidify Williams et al.’s conclusions.
Considering MODIS satellite images from 2005 and 2006, the re-invasion of water hyacinth adds another piece to the puzzle. The NASA Earth Observatory (2007) states that the reappearance of the invasive species coincided with extremely heavy rains. Reexamining Wilson and Williams’ claims, it is clear that Williams et al.’s (2007) worries about stormy El Niño and cloud cover are relevant in this situation as well. In my opinion, this correlation of information between two sources in two different time frames shines in favor of Williams’ argument. Also, Williams et al. (2007) use more area-specific graphs which seem to more accurately depict the water hyacinth problem. I agree with Wilson et al. (2007) that biological control is essential in controlling the water hyacinth invasion, but Williams et al. (2007) present more convincing data. Hopefully, we will be able to find the ideal balance and solution to maintain control 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.