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.
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