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.



7 Responses to “The Complexities of Eradicating the Water Hyacinth: Was it Biological Control or Mother Nature?”

  1.   Scott Valentine Says:

    What does this mean for the future of water hyacinth on the lake? If it was able to make a resurgence after a period of such a large decline it looks bleak for the future of water hyacinth populations, as if the weevils are not nearly as successful as they appeared to be earlier. It looks like the combination of these two forces worked really well, but the fact remains that there is no control over El Nino weather patterns. What will this this mean? we will need a new approach to the hyacinth problem?

  2.   Kirstin Dolan Says:

    I like the way you set up your argument. You describe the debate, the rationale behind each side, and then your position. The reader needs to understand how a weevil kills a water hyacinth plant and, similarly, how El Nino conditions affect the plant in order to understand the debate. Be careful of grammatical and typographical errors. Too many will cause the reader to loose confidence in your argument.

  3.   Nancy Anderson Goodridge Says:

    I agree with Kristin that your argument is well represented but the writing should be error free. You have sided with Wilson for good reasons, when considering just his and Williams’ viewpoints, but what about the resurgence? Is it your view that there’s a weevil cycle that will reduce the population, then let it rebound, then reduce it again, such that there’s a 3-5-year roller coaster? And if it turns out the weevil needs a helper, would you endorse the introduction of yet another bio-solution? Or is one enough and now it’s time to use other means of control in combination?

  4.   josephbuddy Says:

    That was really interesting. I think mother nature doesn’t need our help on that time of crisis because it was capable of gaining biodiversity back. Although we don’t know how El Niño developed but it was an act of nature and it may have bad effects on some living things but it also has a purpose like controlling over populated species. And for those weevils, they will actually find their way to those plants without our help. We humans are just too concerned on our economy.

  5.   brian marshall Says:

    I have recently spent four years working on Lake Victoria and I have had previous experience of biological control of water hyacinth. There can be no doubt that the weevils (Neochetina sp) have controlled this weed on Lake Victoria and everyone seems to have forgotten what the situation was like before the weevils were introduced. Every plant that I examined around the lake, except for very new and very young growth, was damaged by these insects.

    The notion that the El Nino was the primary cause, or even an effective contributor, to the decline of the weed seems unlikley, and I believe that the relation between the two is coincidental. In support of this argument, I look at the situation in Lake Chivero, Zimbabwe, where I worked for many years. Here, mid-winter air temperatures can fall to zero centigrade, or even below zero, and the water hyacinth became severely frostbitten, the leaves turning brown and shrivelled and the plants seemed to be dead. Yet, within a month or two the water hyacinth was once again growing rapidly and becoming a problem. It was finally brought under control by the introduction of the weevils. When one appreciates how hardy these plants are, it seems inconceivable that a spell of cloudy weather and reduced light intensity could have any lasting effect on it.

    The supposed reurgence of water hyacinth on Lake Victoria, and its supposedly distrous impact, makes good copy and is a way of persuading donors to part with money. The situation is worst in the Nyanza Gulf, Kenya, for a variety of local reasons, but nothing like it was a decade ago – in the rest of lake this plant is no more than a minor nuisance. There is no evidence of a 3-5 year cycle of weevil abundance or of a resurgence of water hyacinth on the lake.

  6.   sc153 Says:

    Professor Marshall, thank you so much for commenting on our class blog. My students and I have only read the two Aquatic Botany brief communication articles (Wilson et al. 2007 and Williams et al. 2007), and thus our perspective on this issue is limited. It is great to hear from someone who has done extensive research on African lakes! –Sandra Cooke

  7.   Nikki Rigl Says:

    I agree with Kristin that your argument is well represented but the writing should be error free. You have sided with Wilson for
    In response to Nancy, I too question your reliance on Wilson’s statements since he does not adequately explain the resurgence of the water hyacinth. His reasonings seem plausible but they are not carried out to explain the whole predicament at hand. The roller coaster you mention is a concept that was mentioned in the article that I also thought was interesting and could likely account for the resurgence seen. It is my opinion that it is better to be safe than sorry. From this perspective I think introducing another control of some kind, be it chemical or biological or physical, would be extremely beneficial. Just as in combating diseases I think that combination therapies prove the most effective.

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