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