Posts Tagged “Lake Victoria”

Despite their damage to the environment, invasive species often grow unchecked, smothering the natural community with unbridled proliferation. Such is the case for the water hyacinth (Eichhorinia crassipes), an aquatic plant that has taken over waterways in North America, Asia, and Africa. The plant has plagued Lake Victoria, one of the hardest hit water bodies, since its introduction in the 1980s. Water hyacinth is a particularly successful invader because it can withstand great variations in salinity and temperature, allowing it to inhabit a variety of locations. Furthermore, it can reproduce asexually at an astounding rate. Though it quickly becomes invasive, the negative effects of the water hyacinth can be long lasting and irreparable.

Water hyacinth spreads across the surface of a water body, blocking light to species below. This creates a cascade of effects because decreased photosynthesis causes dissolved oxygen levels to decrease, harming other members of the ecosystem. Furthermore, the plant’s large biomass hinders boating, a problem that has been particularly devastating to the community of fishermen surrounding Lake Victoria. Indeed, their catch was reduced by as much as 45% at the peak of the invasion.

Past methods to control the spread of the water hyacinth have yielded only temporary reductions in the plant population. Both biocontrol and herbicides have provided temporary relief from the water hyacinth, but these control methods are expensive, and they come with other environmental effects. As a result, they do not always garner support in the community, which makes their implementation less effective. Given the water hyacinth’s damage to both the environment and the surrounding community, how can we incentivize companies to implement water hyacinth control methods?

Sammy Brunell has been researching the most effective methods to eradicate the water hyacinth while appealing to the greater financial interests of the regions surrounding Lake Victoria. A control method that contains the water hyacinth with an additional financial incentive for the community could create lasting environmental and financial benefits for the region. Brunell proposes a containment method that entails harvesting the plant then using its biomass to produce ethanol, which can then be burned for energy.

The process requires the plant to be fermented using various yeasts. Brunell’s experiment will test the effectiveness of several strains of genetically modified yeasts and enzymes in efficiently fermenting water hyacinth. He sees this genetic modification to be the key to making the process a viable solution. Though past experiments have only used naturally occurring yeasts and enzymes, genetically modified designs could improve the process substantially. Brunell also plans to test the application of warm and cold temperatures to examine their effects on the project’s efficiency. He believes his control method will “make [the] public aware that hyacinth can serve a good purpose if utilized the right way.”

Brunell expects this technology to have wide-reaching effects throughout the community surrounding Lake Victoria. Not only will fishermen be able to use the lake, but the surrounding community will have an additional source of income. Brunell says, “My results will hopefully revamp the infrastructure of African nations around Lake Victoria; they can use hyacinth to produce ethanol and fuels to power houses, cities, cars, etc., while also hopefully controlling the advancement of water hyacinth through human consumption.” In the future, he foresees on-shore generators to easily turn the water hyacinth into a necessary fuel source. Brunell’s control methods could be a permanent and self-sustaining solution for the water hyacinth problem on Lake Victoria.

Comments 6 Comments »

The Lake Victoria that European explorers found long ago no longer exists. Today, the lake is dominated by water hyacinth, a non-native, free floating aquatic plant. During the last hundred years, this plant exploded from a small domestic population to a dominate piece of the lake’s ecosystems. In 1995, the size of the water hyacinth populations composed nearly 77 square miles of the lake with added detrimental effects (NASA). However, in 1995 researchers tried to halt the spreading hyacinth and potentially destroy it. Bio-control via the weevil Neochetina was tried, and accordingly the following decade saw an unprecedented decrease in hyacinth populations along Lake Victoria. The question, “why did this happen?” however, is not as clear as it would seem. There are two sides: on one, Wilson et al. argues that the use of weevils as bio-control accounts for the decline. On the other, Williams et al. points out that there is a chance El Niño weather effects played a significant role. This debate was further complicated in 2006 when satellite imagining (NASA) was released showing hyacinth resurgence along Lake Victoria. The real success of the bio-control is now in question, and the future of Lake Victoria lays in its resolve.

Wilson et al. plays up the impact of the weevils on the water hyacinth. They approach the problem by accounting for the population of hyacinth over the entire lake. This is problematic since Lake Victoria is a huge lake and covers a significant amount of diverse area, leading to an over-simplification of the data. However, the best way to overview the condition of the lake is through a broad lens. William et al. takes the former stance. They argue that since the lake is large and many of the areas are geographically diverse, these areas must be measured differently in order to determine the effects of the weevils and the weather. By examining areas of the lake which were less affected by El Niño and comparing it to areas more affected, Williams et al. found that this had a significant impact on hyacinth populations. Ultimately, the evidence of both the papers and the NASA article points to Williams et al’s conclusion: that a combination of the two forces contributed to the decline in hyacinth on Lake Victoria.

Williams et al. make an excellent point at the end of the paper: “As such the El Niño associated weather has not ‘confused the issue’ but rather nature is complex.” This is the essence of why, despite data, I found Williams et al. to be the stronger side to the issue. Nature is an incredibly complicated thing, and humankind still does not even understand how certain cubic centimeters of this planet work. How does that compare to a 26,600 square mile lake? Ultimately, giving credit to one aspect of the hyacinth population is over simplifying the issue, and El Niño is a big enough force to account for a significant influence on the population. This, the over simplification of natural forces, is It Wilson et al.‘s biggest flaw.

This reason alone is not enough to choose Williams et al. over Wilson et al. The article from the NASA earth observatory is what pushed the balance to the side of Williams. In this article, the resurgence of hyacinth is described shortly after the authoring of both of the papers and the end of the El Niño event. This resurgence most likely points to the absence of El Niño since weevils should have worked as a continual and sustainable method of bio-control. When El Niño ended and weevils continued their work, the hyacinth came back. Therefore, it is much more reasonable to attribute the decline of hyacinth earlier, though certainly not all of it, to El Niño instead of the weevils.

Despite the conflict between these two papers and new evidence brought to light. The realization is not that water hyacinth decline was caused by El Niño or by the weevils, but rather that this situation is still poorly understood. Ultimately, these papers show that there is a great need for a much more complex understanding of the many natural forces on Lake Victoria, and until this happens, neither side will be right.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria.  http://earthobservatory.nasa.gov/IOTD/view.php?i=7426. Viewed 24 Jan 2011
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

Comments 4 Comments »

Many plants are introduced into a foreign region because they are highly praised for their aesthetic complexion; however their potentially harmful and destructive consequences are often overlooked unknowingly and unintentionally. Similar to this was the water hyacinth plant that was believed to have been accidently introduced to Lake Victoria in 1989, from a local pond.  Due to its versatile characteristics and wide range of tolerance levels, the water hyacinth has been able to dominantly flourish and disrupt several large bodies of water everywhere in the world except Europe. After its drastic population decline in 2000, several scientists have disputed on what was the leading force of maintaining the water hyacinth levels at low levels. Both scientist, Adrian E. Williams and John R.U. Wilson, agree that the hyacinth weevils and the El Nino event contributed to the water hyacinth decline , however both heavily disagree as to the  relativity and measure of impact that both the weevils and the El Nino event had on the water hyacinth plant. Whereas Williams argues that El Nino was the driving force of the decline of the water hyacinth, Wilson strongly believes that without the weevils the water hyacinth decline would have not been so extreme.

Within a matter of a few years after its introduction to Lake Victoria, the water hyacinth population had exploded into a massive population size, contributing to the loss of native plants and aquatic species, consequently resulting in the loss of biodiversity, a decline in the economy, and the formation of habitats infested with disease carrying insects. With numerous detrimental dilemmas, local biologist took action and introduced weevils in to Lake Victoria in 1996, as a method of biological control. Weevils are successful in which they puncture holes in the leaves of the hyacinth plant and deteriorate the inside of the stems, collectively resulting in the drowning of the plants. Coincidently, 1997/1998 happened to be the year of El Nino, an event where weather patterns are intensified and the surrounding region encounters abnormal weather conditions.  During this time Lake Victoria had experience cloudy weather, contributing to harsher waves and prohibiting (what William argues) light penetration for plant growth.

Wilson explicitly argues that the introduction to weevils is the primary result of the decline in water hyacinth population.  Although Lake Victoria did not see drastic decline until after the El Nino event, Wilson argues that it typically takes 3 to 5 years for the weevil population to reach stable levels and establish their threshold within the lake.  Four years after their introduction  the water hyacinth plant declined from  20,000 hectares to under 1000 hectares.  Wilson elucidates on the fact that since the water hyacinth had already incurred so much damage internally and externally, the intense wave action and winds caused by the El Nino event merely added additional stress factors to the already dismantled plant.  Wilson essentially argues that the weevil’s actions in disintegrating the plants made it more permissible for the plants to be completely ripped from their stationary position by harsh waves and winds.

William argues that while the introduction of weevils might have played some role in the water hyacinth population decline, that it is without a doubt that El Nino’s weather pattern was the main driving force. With lower light penetration, Williams believe that it can prevent plant growth and reproduction.  Other factors included intense wave action, humidity, and water quality.  Williams argue that Lake Victoria is too big of a lake for the weevils to have a significant effect and that without the weather patterns of El Nino, water hyacinth population levels would not have rapidly decline.

After gaining insight on both scientist arguments, I find myself sharing similar views with Wilson. I do agree that both the El Nino event and the introduction of weevils played major roles in the decline of the water hyacinth, however without the introduction of weevils, the internal and external structures of the hyacinth plant would not have been as weak for wave action to completely dismantle the plant. The weevil began the process and would have finished their job, the El Nino event simply fasten the process.

Comments 7 Comments »

The Essence of the Debate

In the early 2000’s, scientists noticed a significant decrease in the water hyacinth population of Lake Victoria in Africa. Two groups of scientist, Wilson et al. and Williams et al., have attributed various factors to this result. In a 2007 issue of Aquatic Botany, Wilson et al., which included Dr.James Ogwang, suggested that biological control by Neochetina spp, the South American weevil, was the major reason for the decline in water hyacinths on Lake Victoria. Williams et al. published an article in Aquatic Botany that same year challenging Wilson’s et al. claim. Williams et al instead argues that during 1997-1998 the climatic effects of an El Nino, cloud cover and increased wave action was responsible for the decline in water hyacinths. Specifically, Williams et al believed cloud cover decreased the growth rate of the water hyacinth, a photosynthesizing plant, and then increased wave action broke up, and drowned a majority of water hyacinths and weevils in process.

Method of Data Collection and Presentation of Data

Wilson et al utilized satellite images of Lake Victoria at various times to estimate the amount of hyacinth coverage for the entire lake.  Next they created a graph showing the amount of hectares covered by water hyacinths from 1996 to 2002. The graph also indicated the period when the weevils were introduced to three different areas by Dr. Ogwang, and the occurrence of the El Nino weather pattern. Williams et al. also used satellite images from various time periods to measure water hyacinth coverage on Lake Victoria. However unlike the other group, Williams et al estimated water hyacinth coverage separately for the Tanzanian, Ugandan and Kenyan (Winam Gulf) sides of the lake, the same three areas where biocontrol was implemented by Dr. Ogwang. They then produced three graphs showing the hyacinth coverage (hectares) between March 1994 and September 2001, and the time of biocontrol implementation for each region.

NASA Reveals a Startling Result 

 However while both group of scientists attributed different reasons for the decline in the hyacinth’s population, satellite imagery provided by NASA article in 2006 shows resurgence by the invaders. From the date of the image it appears odd and irrelevant for both groups to argue about the decline in the population when there’s clearly a problem. One must note however that these articles were initially submitted in 2005 and edited during early 2006. These articles were already in the publishing phase when the satellite image was presented by NASA.

Both groups attribute each other’s respective factor for playing a minor role in the decline of water hyacinths on Lake Victoria. However each group believes their respective factor was the major cause for the decline, and had strong arguments to support their claim. I agree with Williams’ et al. that “reduced incident light [caused by cloud cover] reduced the growth rate of a photosynthesizing plant [water hyacinth]”. However I do not believe that reduced incident light could have had that significant an impact. Fig. 1 in Williams’ et al.  article indicates that the El Nino was present over a course of approximately six months, but cloud cover couldn’t  have been absolutely continuous over the course of those six months. I also think that wave action might have contributed to the resurgence of water hyacinths for as mats are broken up water hyacinths along with their seeds spread to new areas of the lake. To me biocontrol seems the more plausible and relevant factor in the decline of water hyacinths in Lake Victoria.

References: 

 NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 24 Jan 2011.

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.

Comments 2 Comments »

In recent years, Lake Victoria has been struggling to cope with the introduction of the water hyacinth plant, which has been clogging the lake and destroying aquatic life there. To combat the invasive and aggressive hyacinth, ecologists introduced Neochetina, or weevils, in 1995,  to eat away at the hyacinth and thwart its expansion.  After years of studying the plant’s disappearance and reappearance, scientists debate over what caused the disappearance of the hyacinth; Was it the biological control through weevils? or, was it the rainy El NiNo weather  pattern that flushed the hyacinth from Lake Victoria?

Wilson’s article seems to conclude that although El Nino played a part in the disappearance of the hyacinth, the main driving force was the introduction of the foreign weevil species. Wilson’s data shows that there was a decrease in hyacinth due to El Nino, however, the hyacinth would come back and regroup. only in 1999, about 5 years after the weevils were  introduced, did the hyacinth population really begin to decline.  These 5 years were necessary for the weevil population to grow and damage the hyacinth.

Neochetica larvae do a great job of eating through the roots and petioles of the hyacinth, which in turn allows bacteria and fungi to invade the plant. Also, with increased holes in the roots and stems, the hyacinth mats becomes very water clogged and tend to sink to the bottom of the water, which allows it to be flushed out of the system easily.

Wilson’s main argument resides on satellite images taken by Albright et al, which show an increase in the hyacinth population through 1998, and then declined slightly in 1998 , only to increase more through 1999. Scientists thought the weevils weren’t doing their job, but starting in 2000, the hyacinth populations began to decrease greatly. Wilson argues had the weevils not weaken the plants, El Nino would have never been able to pull out the hyacinth.

Williams presents Albright’s data in a different way, on that seems to make more sense. Williams critiques Wilson by questioning his ability to measure the hyacinth population for the entire Lake Victoria, its simply too big. Instead, Williams charts show hyacinth growth in the Tanzanian,Kenyan, and Ugandan portions of Lake Victoria.

In the graphs, Williams’ takes note that regardless of when the weevils were introduced, the biggest drop in hyacinth was during the 97/98 El Nino event. He also makes mention of another factor that may have reduced hyacinth growth; light. El Nino is a very wet and cloudy weather pattern, thus denying the hyacinth sufficient light to perform photosynthesis and multiply. That, coupled with high tides and flooding, were the main factors flushing hyacinth out of Lake Victoria, according to Williams.

Given the evidence presented and the distinct introduction of weevils into Lake Victoria, I think it is impossible to claim that weevils weren’t the driving force behind the hyacinth disappearance. For one, El Nino had already stormed through the lake before weevil introduction, and hyacinth populations didn’t diminish, because the plant was strong and rooted. Weevils did their job, trying to destroy as many plants as possible, but failed to flush away the plants without El Nino patterns.

In reality, the biological control method only solved short term problems in reducing hyacinth numbers. Weevils can only try kill the plant, thus leaving mats of hyacinth plants on the ocean floor.  Hyacinth is too versatile of a plant; it can grow on any surface that the mats land on. El Nino was the best support in flushing away the mats out of the lake and shrinking hyacinth numbers, but that just raises questions about manual removal of hyacinth. Is it not possible to better regulate the removal of plant matter after weevils dissemble hyacinth from its roots?  Because  given the current trend, dead plant matter will continue to accumulate on the lake floor and continue to clog its waterways.

Comments 2 Comments »

The water hyacinth was brought to Lake Victoria through a love story, or so it is thought. In 1989, a foreign engineer from South America fell in love and as an engagement present, gave his fiancé a water hyacinth. As their love grew, so did the plant. As it grew, pieces of the plant somehow escaped and found their way to Lake Victoria. The sad side of this love story, however, is that over the years, the water hyacinth transformed from a symbol of love to an invasive species in Lake Victoria.

A water hyacinth is a weed. By 1995, it covered 80% of Lake Victoria, which is the world’s second largest lake located in central Africa (Wilson et al 2007). The plants clog shorelines making it disastrous to people. Fisherman struggle with reduced numbers of fish, which in return threatens famine for the region. Civilians struggle with dirty drinking water caused by the water hyacinth’s rotting vegetation. Also, the weed creates breeding areas for mosquitoes and for parasites to lay eggs, thus further causing a bad situation for the lake’s human and animal inhabitants.

To deal with this increasing problem in Lake Victoria, Neochetina weevils, native to Brazil, were introduced through bio-control in the mid-1990′s. This process involved introducing a foreign organism, as an enemy of an existing organism, in hopes of getting rid of that existing organism. Weevils are natural enemies of the water hyacinth. These small insects chew holes in the leaves of the water hyacinth allowing bacteria to enter and cause severe damage to the plant.

Further, in 1997/1998 El Nino, a severe weather pattern, accompanied the water hyacinth reduction. This weather pattern brought storms with heavy rains, wind, and cloudy skies in the region. The severe weather change occurred around the same time that the weevil population was growing and the water hyacinth population was obviously decreasing.

In 1996, as the numbers of water hyacinth plants in Lake Victoria continued to decrease, scientists began to question what was actually responsible for the water hyacinth reduction.  Researchers debated whether it was the bio-control through the weevils or weather conditions through El Nino.

According to Wilson et al. (2007), who published his article in “Aquatic Botany”, a scientific journal, the weevils were the primary cause of reduction, however, El Nino hastened the process. After taking satellite images of Lake Victoria, Wilson concluded that bio-control was the only method that was utilized throughout the whole of Lake Victoria. Also, Wilson believed that the high winds and large waves caused by El Nino added to the stress of the already weakened water hyacinth causing the plants to separate from their pods and sink more quickly. Moreover, Wilson believed that the resurgence of water hyacinth would not happen.

On the opposite end of the spectrum, Williams et al. (2007), believed that although there was reduction in water hyacinth when the weevils were first introduced, the main reduction happened during El Nino, as stated in his article published in the “Aquatic Botany”. The greatest reduction happened during El Nino because the cloud coverage limited the amount of light the water hyacinth received reducing its levels of photosynthesis. Consequently, the plant suffered reduction in growth and reproduction rates. Thus, El Nino was the main cause of the water hyacinth destruction.

In conclusion, I believe that each scientist is correct in giving both the weevils and El Nino credit for the water hyacinth reduction. The weevils weakened the water hyacinth and El Nino provided the final “push” to destroy the water hyacinth. Without, El Nino I do not think that the weevils could have solely gotten rid of the water hyacinth and vice versa. Thus, I believe William’s argument over Wilson’s. I believe that the weevils did the hard part by weakening the water hyacinth and El Nino finalized the reduction. In regard to the resurgence, I believe that El Nino is a very rare occurrence and therefore, it makes sense to me that the water hyacinth could resurge. The weevils need the help of Mother Nature, as Mother Nature needed the help of the weevils.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria.  http://earthobservatory.nasa.gov/IOTD/view.php?i=7426. Viewed 24 Jan 2011
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

Comments 3 Comments »

Water hyacinth has been a menace to all who depend on Lake Victoria since its proliferation in the early 1990s. The aquatic plant forms a dense mat over the surface of the water, blocking sunlight and deoxygenating water, to the detriment of all native species. The vegetation stills water flow, which creates an ideal breeding ground for disease-carrying mosquitoes. (NASA Earth Observatory, 2007) Indeed, there has been a significant increase in the incidences of malaria, dysentery, schistosomiasis, and other diseases, according to the 2005 documentary series “Strange Days on Planet Earth.” Water hyacinth is also a dire concern for subsistence fishermen on the lake because the mats hinder boating. Finally, the dense growth has widespread consequences in the surrounding regions because it clogs intake valves in hydroelectric plants and fouls drinking water. Clearly, it was necessary for the people who depend on Lake Victoria to take action towards containment, if not eradication, of the water hyacinth.

Responding to the desperate situation, scientists implemented classical biocontrol methods in an effort to weaken and kill the population of water hyacinth. In biocontrol, scientists import natural enemies, in this case the weevils Neochetina bruchi and Neochetina eichhorniae, to harm the invasive plant, which usually lacks predators in its new location. Adult weevils damage water hyacinth by consuming its leaves, while larvae tunnel through its roots and stems. The combination opens the plants to secondary infection and causes them to sit lower in the water, according to Wilson et al. (2007), who claim the 2000 reduction in water hyacinth population was caused mainly by the weevils.

There has been recent controversy over whether the reduction of water hyacinth was due to biocontrol or natural weather events, such as the El Niño of 1997-1998. Wilson et al. (2007) argue that, while El Niño contributed to the water hyacinth decline, it can mostly be attributed to the weevils because they weakened the plant. They claim that the low light levels during El Niño did not harm the plants severely enough to cause their rapid decline. Williams et al. (2007) dispute this claim, saying prolonged suboptimal light would weaken the plants and make them vulnerable to other weather-related factors, such as wind, waves, and water quality. They also claim that the weevil population was too unstable after El Niño to cause a lake-wide reduction in the water hyacinth population, arguing that the severe weather patterns played a larger role in the water hyacinth decline. Both teams of scientists agree that both biological control and weather factors played a role in reducing water hyacinth prevalence, but they disagree as to their respective magnitude.

In my opinion, Williams et al. (2007) provide the more convincing argument. Wilson et al. (2007) maintain that the use of weevils in biological control usually takes 3-5 years on large bodies of water. The reduction of the water hyacinth population 3-4 years after the weevil was introduced would make sense in the absence of the El Niño event. However, they state that the weevil population was decimated when the large mats sank as a result of wind and wave action. It is doubtful the weevil population could recover fully enough after such a reduction in population size to eradicate the plant on their predicted schedule. Water hyacinth control could be more believably attributed to the weevil if the massive population reduction had occurred several years later. Furthermore, photos taken by NASA in 2007 showing a resurgence of water hyacinth may point to environmental factors. If the population of weevil had been large enough to cause the massive water hyacinth decline, they would have been able to maintain control. However, if environmental factors were the primary cause, the end of the weather event could allow a second invasion.

In reality, the initial decline of the water hyacinth population on Lake Victoria would have been less likely without both the weevil and the El Niño. For a permanent reduction in the water hyacinth population to take place, we cannot rely on unpredictable weather patterns for control. Biological control methods are necessary to keep the population in check. However, for biocontrol to be effective, especially in a body of water as large as Lake Victoria, all populations of weevils must be highly monitored and kept in good health.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria.  http://earthobservatory.nasa.gov/IOTD/view.php?i=7426. Viewed 24 Jan 2011
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

Comments 4 Comments »

Water hyacinth is an invasive plant that was first introduced to Lake Victoria in 1989 ( Wilson et al. 2007). The species spread quickly, infesting about 77 square miles of the lake  by 1998 (NASA Earth Observatory 2007). This has become a huge problem, threatening the biodiversity of the lake, contaminating drinking water, and hampering transportation. In order to remove the aggressive species, biological control agents were released into different parts of the lake in 1995. There was also an El Niño weather pattern during 1997/1998, around the same time water hyacinth populations started to decline. Recently, there has been some debate over the cause of the decline of water hyacinth on Lake Victoria. Some researchers argue that without the presence of weevils, the control agents that eat water hyacinth, the population crash would not have occurred. Others disagree, saying that the wet and cloudy weather of el Niño played a major part by accelerating the decline through direct effects.

In an Aquatic Botany article, Wilson et al. (2007) claims that, although el Niño hastened the destruction of water hyacinth, the presence of weevils was the major contributor to the rapid decrease. Satellite images of water coverage were analyzed and then summarized on a graph, showing the trend of how lake-wide water hyacinth populations changed over time. They agree that increased wind and wave action from El Niño may have been a major stress to plants, but their data shows that the major turning point was in 1999, when the weevils finally became effective.

Williams et. al (2007) combats this opinion in another Aquatic Botany article, stating that el Niño was the major cause of the water hyacinth destruction. Wilson’s article is criticized for condensing the system into an “oversimplification of the spatial complexity”(Williams et. al 2007). They argue that the collapse could not be fully attributed to the weevils because they were introduced 4 years prior to the rapid reduction. There was also a concern of resurgence of the plant because weevils have never become established within the river systems around Lake Victoria. An infestation of weevils must occur before biocontrol can take affect.

Little did they know that in December 2006, satellite images revealed that water hyacinth was back (NASA Earth Observatory 2007). For Wilson, this must have been a hard thing to comprehend. The resurgence of water hyacinth, in my opinion, supports the Williams article. I also agree that Wilson oversimplified years worth of data onto one chart; I was skeptical that the analysis was accurate. Also, their approach was not restricted to dates where the whole lake was clear from cloud cover. Therefore, the Williams article provided the most convincing argument with the data.

In light of the MODIS satellite images that showed images of growing water hyacinth populations, it can be said that biocontrol in general does not always work, and can sometimes turn out for the worse. In this case, the weevils were not acclimated to the size and environment of Lake Victoria, and therefore did not thrive as well. In order for biocontrol to be effective, a large scale infestation must occur; this could take years. The biocontrol must also be regulated frequently; as water hyacinth starts to die off and rot, the weevils also die from rotting plants or lack of food. On broad terms, invasive species pose major threats to our society and environment, and biocontrol should not be taken for granted.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria.  http://earthobservatory.nasa.gov/IOTD/view.php?i=7426. Viewed 24 Jan 2011
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

Comments 3 Comments »

css.php