Weevils + El Nino < Hyacinth

January 27, 2010

In 1989, water hyacinth first appeared on Lake Victoria.  Without natural enemies to control its spread, it quickly expanded and became a troublesome invader to the ecosystem.  By 2000, the population had been brought back to a reasonable level, and there are two competing explanations for this decline: weevils and the El Niño weather pattern in 1997-1998.

According to Wilson et al. (2007), the main cause of the hyacinth decline was the introduction of weevils into the area, an insect that feeds on the plant, causing it considerable damage.  The weevils were brought as a means of biocontrol, and Wilson et al. (2007) claim that they weakened the hyacinth, making it more susceptible to the inclement weather, and then finishing off the remaining hyacinth that surged in the aftermath of El Niño.  They specifically cite the fact that the four years it took for the hyacinth population to be fully controlled is consistent with the time frames that occurred in weevil biocontrol of hyacinth in other areas, as well as the fact that the hyacinth population started to flourish again after El Niño, suggesting that the stormy weather alone did not cause its eventual downfall.

Williams et al. (2007), on the other hand, argue that it was in fact the El Niño weather pattern that played the biggest role.  They point to Lake Victoria’s size and diverse range of habitats, claiming that Wilson et al. (2007) oversimplify the true nature of the hyacinth’s decline.  By looking at the data for each section of the lake, Williams et al. (2007) show that nearly all hyacinth not in a sheltered gulf area was eliminated simultaneously in late 1997 to early 1998, the same time as the El Niño event.  They acknowledge that weevils no doubt played a large role in weakening the plants, but assert that Wilson et al. (2007) give too much credit to the success of the biocontrol.

Ultimately, later photos revealed that water hyacinth has returned to Lake Victoria in extreme quantities in the sheltered Winam Gulf area.  I believe that this suggests that Williams et al. were more correct in their analysis of the situation, as it appears that, in the area of Lake Victoria that was protected from the worst of the El Niño weather, the weevils alone were not enough to eliminate the hyacinth in the long term.  Nonetheless, both sides emphasize the fact that the decline was due to a variety of factors, and neither can be considered completely correct, since water hyacinth never was truly eliminated.  On a wider scale, this leads one to wonder how successful any biocontrol effort can ever be, and if perhaps all one can do is forestall the inevitable.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-Invades Lake Victoria.
http://earthobservatory.nasa.gov/IOTD/veiw.php?id=7426. Viewed 27 January 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. Katagaria, 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


The Water Hyacinth Debate Debunked

January 27, 2010

Emilia Rybak

Ever since water hyacinth was first reported on Lake Victoria in 1989, this invasive species has wreaked havoc on the lake and the valuable biodiversity that depend on it for survival. Although there is no disagreement regarding how much destruction water hyacinth has caused, there is an ongoing debate concerning the factors that brought about its decline in 1998.

Some scientists agree with the argument presented by Wilson et al. (2007) that wet and cloudy weather patterns caused by El Nino played a vital role in the water hyacinth’s decline in the second half of 1997 and the first half of 1998. However, others believe that, as Williams et al. (2005) argue, that the introduction of Neochetina spp., or weevils, in Lake Victoria as a form of bio-control was responsible for this drop.

Specifically, Wilson et al. state that the four-year gap between when weevils were introduced in Lake Victoria in 1995 and when they started to produce results is consistent with results of other bio-control agents in other countries. Thus, they argue that weevils were primarily accountable for the water hyacinth decline since their effects occurred in accordance with those of other species. On the other hand, Williams et al. assert that prolonged sub-optimal light will reduce growth and reproduction rates of plants while enhancing the results of other debilitating forces, including weevil herbivory. Therefore, the stormy weather in 1998 provided ideal conditions for impeding the spread of water hyacinth, and thus aided the weevils in declining the water hyacinth population.

I think that the argument of Williams et al. is more convincing since it acknowledges that El Nino weather patterns were not solely responsible for causing the decline in water hyacinth, but rather that the combined effects of El Nino and the weevils enabled the decline. Even if the weevil population did only begin to produce results after four years, it is undeniable that the El Nino patterns contributed to their efficacy.

The MODIS satellite images taken in 2005 and 2006 that display the resurgence of water hyacinth on Lake Victoria demonstrate that bio-control is not a fully reliable method of managing invasive species. They show that bio-control may sometimes be an effective strategy, yet its efficacy often falls short. Thus, scientists should not completely depend on this method to eradicate an invasive species, and both invasive species and bio-control agents should be regularly monitored to avoid resurgences.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-Invades Lake Victoria.
http://earthobservatory.nasa.gov/IOTD/veiw.php?id=7426. Viewed 27 January 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. Katagaria, 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


There’s something about Weevil

January 27, 2010

Since its introduction in the late twentieth century, water hyacinth has been a major nuisance in Lake Victoria.  Not only does it pollute the water by disrupting the lake’s flow, but because of the plant’s massive undergrowth, also reduces fishermen’s abilities to make a living and poses as a major threat to native species. To attempt to counteract this invasive species, in 1995, weevils, which are small herbivore beetles and natural predators of water hyacinth, were released into the water hyacinth clusters as biological control agents.

However, according to Williams et al. (2006), though the weevils aided in the reduction of water hyacinth in Lake Victoria from 1999 to 2000, they were not the main reason for the plant’s reduction. Another factor, the El Nino of 1997 – 1998, which had been the biggest ever recorded in the twentieth century, was, according to Williams et al. (2006), the most important contributing factor to the water hyacinth’s decline. Williams et al. (2006) argues that it was because of a combination of timing, reduced sunlight, and weevils, that the decline of water hyacinth in 1999/2000 was so dramatic. Therefore, Williams et al. (2006) warns that now the El Nino has calmed, the water hyacinth will resurge; the weevils will be unable to keep the plant population under control.

Wilson et al. (2006), on the other hand, argues that the weevils were crucial, if not the only factor in the water hyacinth’s decline, and that the El Nino had little effect on the plant’s growth. This is because, according to Wilson et al. (2006), the weevils generally takes three to five years to fully reach their potential and the decline in water hyacinth fits that timeline perfectly in accordance with the three releases of weevil nests into the water hyacinth clusters. The El Nino, on the other hand, though would have moved already weevil-weakened water hyacinth mats around, could not have had reduced water hyacinth growth by increased cloud cover; there is no substantive link between low light and water hyacinth concentration. (Wilson et al., 2006)

In light of all the evidence, I think that Williams et al. (2006) gives a more convincing argument than Wilson et al. (2006), because the latter neglected many sides of the former’s argument, and did not even consider the possibility that water hyacinth might return, even if it weren’t because of the El Nino’s dispersion.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. 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.


SW2: Lake Victoria, let the force of biocontrol be with you

January 27, 2010

Of the many methods used to control invasive species, the use of biocontrol, which often results only in the addition of another harmful invasive species to an ecosystem, is certainly one of the most controversial. Occasionally, however, this method successfully reduces the effects of the original invader.  Some, including Wilson et al. (2007), speculate that one such success story may have taken place in Lake Victoria, where Neochetina was used as biocontrol on water hyacinth, an invasive plant in many parts of the world.  This plant, which lived on Lake Victoria’s surface and ultimately altered its entire ecosystem, began to decline shortly after the introduction of the weevils.  This decline also coincided with changing climatic conditions caused by El Nino, leaving many uncertain of where credit for the plant’s decline belongs.

Examining the effects of weevils and El Nino’s weather conditions on water hyacinth in other areas with similar climates ecosystems may result in the most accurate determinations of why the dwindling of water hyacinth occurred. Wilson et al. (2007) have observed that, in areas with a climate similar to that of Kenya, such as West Africa and Papua New Guinea, the introduction of Neochetina has successfully slowed the invasion of water hyacinth, while low sunlight levels present because of El Nino did not prevent growth, leading us to believe that Neochetina caused the decline.  However, Williams et al. (2007) assert that low sunlight levels, flooding, and waves caused by El Nino caused the demise of water hyacinth in Lake Victoria.

I agree that “changes in plant quality [including those caused by climatic changes] can affect the efficiency of weevils and a rapid deterioration of plants can lead to an early decline in weevil populations … such that plants can recover” (Williams et al., 2007).  However, like Wilson et al. (2007), who acknowledge the effects of these natural Neochetina population fluctuations, I do not believe that the weevil population was disturbed severely enough to negate its effect on the water hyacinth.  The water hyacinth was likely overcome by the combined destructive forces of  Neochetina and El Nino.  Perhaps the recent reinvasion of water hyacinth in Lake Victoria, as shown by images from the NASA Earth Observatory (2007), will allow us to determine whether Neochetina can successfully slow water hyacinth invasion in as a large body of water as Lake Victoria without the weakening of the plant by El Nino.

Sources:

NASA Earth Observatory.  2007.  Water Hyacinth Re-invades Lake Victoria.http://earthobservatory.nasa.gov/IOTD/view.php?id=7426.  Viewed 27 January 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. Katagaria, 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.


Victory!? But Still No Consensus

January 27, 2010

Water hyacinth is a fast growing South American plant which spread along the shores of Africa’s Lake Victoria, forming a blanket that suffocated native species and the fish industry.  To combat this plant, weevils were introduced and several years later the water hyacinth population began to decline.  The biologists responsible for this action have claimed victory; however these claims have been challenged by other scientists who point to atypical weather phenomena as playing a role in the water hyacinth’s decline.

Wilson et al.  (2007) argues that the implementation of biological control by introducing the weevils is primarily responsible for the subsequent decline in the water hyacinth.  They support this conclusion with estimates of total water hyacinth coverage of Lake Victoria extrapolated from satellite data that show a marked decline approximately 3 years after the weevils were introduced.  Also, they note that this result is similar to that of other nations who have enacted this form of biological control and that the introduction of weevils is the only management technique common to all parts of the lake.

The argument that weather phenomena, specifically the El Nino event of 1997/1998 contributed significantly to the decline of water hyacinth on Lake Victoria is expressed by Williams et al. (2007).  They maintain that the lake-wide summaries produced by Wilson et al. (2007) do not respect the diversity and size of Lake Victoria.  Thus, they examine each of the lake’s main sections separately and noticed that the water hyacinth began to decline in all three sections roughly simultaneously after the El Nino event whereas the weevils had been introduced to each region at different times.  Their argument therefore is that the El Nino event weakened the water hyacinth population and left it susceptible to destruction by both the weevils and other factors.

I agree with Williams et al. (1997) that the water hyacinth population of Lake Victoria cannot be accurately modeled as a single graph.  The simultaneous decline of water hyacinth suggests a cause that is universal, not susceptible to regional variation like the weevil population.  The importance of regional considerations was recently highlighted by a report from the NASA Earth Observatory (2007) which found that rain runoff had sparked a rapid resurgence of water hyacinth.  Efforts to control this new growth and prevent future growth should place an emphasis on regional attributes such as agriculture that make a region susceptible to water hyacinth invasion.

Eli Wilber

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.


Watch What You Plant, for Weevil’s Sake! (SW2)

January 27, 2010

When someone plants a water hyacinth to liven up the flora in his garden pond, the idea of initializing the spread of an invasive species is probably not the first thing to come to mind.  Not only does water hyacinth impede Lake Victoria fisherman from doing their jobs, but it also blankets the surface of the lake and prevents underwater aquatic species from getting essential sunlight.  Efforts have been made to mitigate the spread of the water hyacinth, most notably the introduction of the Neochetina weevil to Lake Victoria.  Through these efforts using biocontrol and the effects of El Nino, the water hyacinth population was at a time diminished significantly.  However, the population is only recently starting to once again emerge and thrive in Lake Victoria.

According to Wilson et al. (2007), the decline in the water hyacinth population was primarily due to the Neochetina weevil.  While evidence certainly points to most of the damage to the population being due to the waves caused by El Nino, Wilson et al. (2007) claims that the weevils are what truly kept the hyacinth in check.  The article even goes as far as to say that “the El Nino event may have been a major stress to the plants…[but] the plants were already badly damaged by the weevils” (Wilson et al. (2007)) which just goes to show how the weevils played a major role in water hyacinth reduction.

On the other side of the spectrum, Williams et al. (2007) does not accredit the Neochetina weevil as the chief agent in reducing the water hyacinth in Lake Victoria, but instead the severe weather patterns of El Nino.  Through use of graphs and hard scientific data of hyacinth population through time, Williams et al. (2007) claims that hyacinth population did not actually decline until El Nino caused the waves which uprooted most of the population in Lake Victoria.

While both articles present a clear and convincing reason as to the causation of the water hyacinth population decline, I believe that Wilson et al. (2007) is the more legitimate of the two.  Aside from being a physically longer article, I like Wilson et al. (2007) because it does not beat around the bush in how it admits that the population decline was primarily caused El Nino, but the only reason the damage was possible was because the plants were weakened by weevils prior to El Nino.  Even if El Nino was the main cause for the destruction of the species, it was seen that after the storm the weevil population declined which in turn gave rise to an increase in water hyacinth population.  So in summation, I feel that Wilson et al. (2007) is an overall better article.  Furthermore, if you ever plan on planting  anything, you would be well advised to check if this plant could possibly cause an aquatic invasive epidemic.  If anything, do it for the sake of the weevils.

Sources

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. 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.


Water Hyacinth

January 27, 2010

Water hyacinth is a marine plant native to South America. Over the last few decades, however, it has infested Lake Victoria and made it hard for local fishermen to maintain their lifestyle. Large mats of water hyacinth have clogged waterways, reduced small local marine life, and blocked sunlight from reaching the lake bottom. Recently, there have been efforts to reduce the water hyacinth population, but whether they have been effective or not is another matter.

Williams et al. (2007) states that the waves caused by El Nino ungrounded water hyacinth plants and allowed for their destruction. Another proposed reason for the hyacinth’s disappearance is the fact that thick cloud cover due to the weather conditions blocked out sunlight, and led to decreased photosynthesis and fertility in established water hyacinth plants (Williams et al. 2007). In early 1998, the latter part of a particularly violent El Nino pattern, water hyacinth populations declined sharply.

Wilson et al. (2007), on the other hand, believes that the ultimate reason for the plant’s disappearance was the introduction of weevils as biocontrol – introducing one species to control another. Although the water hyacinth population did decline sharply in early 1998, plant populations steadied and rose again later that year. They didn’t begin to steadily decline until 1999, 4 years after the introduction of the weevils (Wilson et al. 2007), a typical time period as gathered from other weevil biocontrol situations. Wilson et. al (2007) suggests that El Nino harmed the weevil populations, and that the “new growth was able to proliferate in the absence of weevils”. Weevils were also introduced to other areas – West Africa and Papua New Guinea – and successfully reduced hyacinth populations where they were the only method of control being implemented (Wilson et al. 2007).

To me, it is clear that Wilson et al. (2007) presents a stronger argument. Although Williams et al. (2007) introduces many valid points, Wilson et al. (2007) presents its own evidence and nullifies several parts of Williams’ argument. Despite the fact that I believe Wilson’s argument holds more validity, both documents agree that both El Nino patterns and weevil influence helped decrease water hyacinth populations. As data shows, water hyacinth populations are rising again (NASA 2007). Instead of arguing over who’s more correct, I think the real issue here is to focus on the factors we can control (the weevils) while continuing to search for a more secure solution.

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.


SW2: Weather v. Weevils

January 27, 2010

There is much debate as to the efficiency of bio-control on Lake Victoria. Weevils were first introduced as a method to control water hyacinth in 1995. During the first half of 1998 there was a sharp decline in the population, coinciding with El Nino; however, shortly after there was in increase. In early 1999 a steady decline began and continued. There is argument as to whether biological control was the major factor or if El Nino associated weather patterns were the primary cause behind the decline.

Wilson et al. (2007) take the stance that bio-control was the main factor behind the water hyacinth’s decline, although the stormy weather associated with El Nino also played a part. They argue that bio-control typically takes four years to take full affect and this situation stands true in Lake Victoria. They state that biological control agents were the only control measures in place and they cite similar cases where bio-control was effective. They also argue the effects of El Nino explain the seeming resurgence of water hyacinth in certain areas. They conclude by saying that although another resurgence of the plant is unlikely there must be continued monitoring of both water hyacinth and weevil populations.

Williams et al. (2007) state that, while weevils did have a role, the reduction of water hyacinth in the second quarter of 1998 was the result of El Nino. They claim that it was not only due to a reduced light climate, but also water level, wave action, and other weather-related factors. They conclude by saying that they agree that bio-control should continue to be a factor on Lake Victoria, but its limits need to be considered and monitored.

I do believe that bio-control of the water hyacinth has been effective and played a major role in the reduction of water hyacinth on Lake Victoria. However, I agree with Williams et al. (2007) that the decline in 1998 was due to El Nino, but after that time I think that it was the weevils taking effect. However, I think that due to the resurgence proved by the images from NASA Earth Observatory 2007) that the weevils have not been as effective as Wilson et al. seems to think. I think that bio-control is a good option and will continue to be effective, but it definitely has flaws and the situation in Lake Victoria must continue to be monitored.

Tara Porter

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. Aujuonu, 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



The Biological Control in Lake Victoria: Was it Really that Effective?

January 27, 2010

Kevin Shia

SW 2: The Biological Control in Lake Victoria: Was it Really that Effective?

With the proliferation of the water hyacinth in Lake Victoria, it is necessary to discuss aspects of biological control. The debate is to determine if biological controls help reduce the population of the Water Hyacinth in Lake Victoria. The biological factor consists of importing Neochetina weevils into the environment (Williams et al. 2007). The opposing argument is that the effects of El Niño are more significant in reducing the population of the plant. Wilson et al. (2007) believe that the weevils were the main cause for the decrease in the water hyacinth, while Williams et al. (2007) believes that El Niño was the main cause of the decrease in the invasive plant.

Wilson et al. (2007) state that the reason why the Neochetina larvae are so effective in damaging the water hyacinth mats is that they tunnel into the roots and cause massive damage to the whole plant. Wilson et al. (2007) also discredit Williams et al. (2007) by explaining how unlikely it is that the cloudy weather that is associated with the El Niño that occurred during the years of 1997 and 1998 can still affect the decrease of the water hyacinth between 1999 to 2000. They also state the claim that the data of Williams et al. (2007) cannot truly prove the relationship between the low light levels due to El Niño and the mortality of the plants because plants can still grow in low light. Wilson et al. (2007) claim that because the Neochetina population is an unstable host population, it can potentially lead to uncontrollable plant populations. They also claim that the weevils can also cause potential harm to themselves. For example, if the weevils cause enough damage to the water hyacinth, they can make the mats sink lower into the water, which can drown the eggs and larvae and the death of the weevils can proliferate the growth of the invasive plants again (Williams et al. 2007).

Based on the given information from Williams et al. (2007) and Wilson et al. (2007), I believe that both biological controls and the effects of El Niño helped change the total amount of water hyacinths in Lake Victoria. Even though the environmental effects of El Niño assisted with the reduction of the water hyacinth, I believe that the biological controls of the Neochetina weevils were more influential in reducing the growth of the water hyacinth.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria, http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 24 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Wather 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.


Hyacinth Debate Water-logged in Technicality

January 27, 2010

Water hyacinth is an invasive species that harms the ecosystem of Lake Victoria in Africa by creating mats that block sunlight from reaching native species in the water (NASA Earth Observatory 2007). Insects called weevils were introduced as predators of the invasive weed in 1995 in an attempt to solve the problem through biological control (Wilson et al. 2007). A sharp decrease in water hyacinth population was seen by 2000, but the scientific community was not convinced that the weevils caused this change. Williams et al. (2007) released a subsequent paper suggesting that while weevil presence did help reduce hyacinth in Lake Victoria, el niño weather conditions at the time, were more significant factors. They alleged that wave conditions and limited sunlight had more significant effects, also stating that they believed the weevil population was unstable, and monitoring the population would be necessary in preventing a resurgence.
The arguments presented by Williams et al. (2007) seem to be more convincing. A major point made in the article is the synchronous nature of the disappearance of hyacinth. The population decreased uniformly across the lake, suggesting that a larger factor such as weather was responsible for the changes. While Wilson et al. (2007) states that reduced sunlight due to el niño would not kill the hyacinth, Williams et al. (2007) argues that while not fatal, such conditions would seriously impede growth. The Williams et al. article also appears to be more convincing in its logical claim that an unstable host population creates instability in the weevil population, and thus the weevils must be monitored to prevent hyacinth resurgence.
To me, the argument contained within the papers seems to be a moot point. Both sides agree that both factors have some level of influence, and the conclusion of Williams et al. (2007) supports continues use of weevils, fearing their disappearance at the hands of unstable conditions. Since we as humans are not presented with the ability to choose el niño conditions over the use of weevils, we should do what we can and use weevils to try and keep hyacinth populations low. Unfortunately, this did not happen. According to the NASA Earth Observatory (2007), hyacinth populations have returned in full force, once again covering Lake Victoria. Perhaps instead of arguing, both groups should have focused on maintaining the somewhat effective use of weevils and finding a more effective and proven solution.

NASA Earth Observatory. 2007. Water Hyacinth Re-Invades Lake Victoria.
http://earthobservatory.nasa.gov/IOTD/veiw.php?id=7426. Viewed 27 January 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. Katagaria, 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


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