Water Hyacinth

The water hyacinth has been the subject of both much concern and debate over the past years.  It’s dramatic takeover of Lake Victoria in Uganda has sparked a heated discussion on why the invader suddenly receded, though it later came back.  The opposing views were in expressed in Wilson et al, arguing that weevils should be given the most credit for the reduction of the water hyacinth, whereas Williams et. al presented the argument that El Niño should be given the credit.

The Wilson et al. paper presents a strong argument, saying that the weevils introduction to Lake Victoria was the main reason for the water hyacinth’s decline.  Though they acknowledge that El Niño may have had a slight effect on the water hyacinth population, the light levels that got through the cloudy weather as a result of the altered climate pattern would’ve been enough to keep the water hyacinth population alive and growing, so the answer to the question of why the water hyacinth declined muse lie in the biocontrol, or the weevils.  Williams et al. presents essentially the opposite argument,  saying that El Niño’s cloud pattern would’ve blocked out light for the water hyacinth, therefore making it hard from them to photosynthesize and expand throughout the lake.  To back their argument, they cited that this wet and cloudy weather had a detrimental effect upon vegetation throughout other parts of Africa as well, and that the weevils may had a helping hand in the decline, but were in the end, of nominal effect in the larger scheme of things.

I think that Wilson et al.’s argument in favor of the biocontrol makes the most sense, given the dramatic reduction of water hyacinth population after the introduction of the weevils, and the sustained decline even after the passing of El Niño. Though the light levels made have adversely effected the population of the water hyacinth, the light levels despite the cloudy weather wouldn’t have stopped their growth and caused the population reduction.  Though, as MODIS images revealed, the water hyacinth has returned, it just reminds us that when using biocontrol, that constant monitoring is required, and problems with invasive species will be something that our society will have to learn to cope with for many years to come.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 13 Sept 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. 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.

Photo from here.