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