Aquatic Invasive Species

Since its introduction in the late twentieth century, water hyacinth has been a major nuisance in Lake Victoria.  Not only does it pollute the water by disrupting the lake’s flow, but because of the plant’s massive undergrowth, also reduces fishermen’s abilities to make a living and poses as a major threat to native species. To attempt to counteract this invasive species, in 1995, weevils, which are small herbivore beetles and natural predators of water hyacinth, were released into the water hyacinth clusters as biological control agents.

However, according to Williams et al. (2006), though the weevils aided in the reduction of water hyacinth in Lake Victoria from 1999 to 2000, they were not the main reason for the plant’s reduction. Another factor, the El Nino of 1997 – 1998, which had been the biggest ever recorded in the twentieth century, was, according to Williams et al. (2006), the most important contributing factor to the water hyacinth’s decline. Williams et al. (2006) argues that it was because of a combination of timing, reduced sunlight, and weevils, that the decline of water hyacinth in 1999/2000 was so dramatic. Therefore, Williams et al. (2006) warns that now the El Nino has calmed, the water hyacinth will resurge; the weevils will be unable to keep the plant population under control.

Wilson et al. (2006), on the other hand, argues that the weevils were crucial, if not the only factor in the water hyacinth’s decline, and that the El Nino had little effect on the plant’s growth. This is because, according to Wilson et al. (2006), the weevils generally takes three to five years to fully reach their potential and the decline in water hyacinth fits that timeline perfectly in accordance with the three releases of weevil nests into the water hyacinth clusters. The El Nino, on the other hand, though would have moved already weevil-weakened water hyacinth mats around, could not have had reduced water hyacinth growth by increased cloud cover; there is no substantive link between low light and water hyacinth concentration. (Wilson et al., 2006)

In light of all the evidence, I think that Williams et al. (2006) gives a more convincing argument than Wilson et al. (2006), because the latter neglected many sides of the former’s argument, and did not even consider the possibility that water hyacinth might return, even if it weren’t because of the El Nino’s dispersion.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. Viewed 20 Jan 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.

When someone plants a water hyacinth to liven up the flora in his garden pond, the idea of initializing the spread of an invasive species is probably not the first thing to come to mind.  Not only does water hyacinth impede Lake Victoria fisherman from doing their jobs, but it also blankets the surface of the lake and prevents underwater aquatic species from getting essential sunlight.  Efforts have been made to mitigate the spread of the water hyacinth, most notably the introduction of the Neochetina weevil to Lake Victoria.  Through these efforts using biocontrol and the effects of El Nino, the water hyacinth population was at a time diminished significantly.  However, the population is only recently starting to once again emerge and thrive in Lake Victoria.

According to Wilson et al. (2007), the decline in the water hyacinth population was primarily due to the Neochetina weevil.  While evidence certainly points to most of the damage to the population being due to the waves caused by El Nino, Wilson et al. (2007) claims that the weevils are what truly kept the hyacinth in check.  The article even goes as far as to say that “the El Nino event may have been a major stress to the plants…[but] the plants were already badly damaged by the weevils” (Wilson et al. (2007)) which just goes to show how the weevils played a major role in water hyacinth reduction.

On the other side of the spectrum, Williams et al. (2007) does not accredit the Neochetina weevil as the chief agent in reducing the water hyacinth in Lake Victoria, but instead the severe weather patterns of El Nino.  Through use of graphs and hard scientific data of hyacinth population through time, Williams et al. (2007) claims that hyacinth population did not actually decline until El Nino caused the waves which uprooted most of the population in Lake Victoria.

While both articles present a clear and convincing reason as to the causation of the water hyacinth population decline, I believe that Wilson et al. (2007) is the more legitimate of the two.  Aside from being a physically longer article, I like Wilson et al. (2007) because it does not beat around the bush in how it admits that the population decline was primarily caused El Nino, but the only reason the damage was possible was because the plants were weakened by weevils prior to El Nino.  Even if El Nino was the main cause for the destruction of the species, it was seen that after the storm the weevil population declined which in turn gave rise to an increase in water hyacinth population.  So in summation, I feel that Wilson et al. (2007) is an overall better article.  Furthermore, if you ever plan on planting  anything, you would be well advised to check if this plant could possibly cause an aquatic invasive epidemic.  If anything, do it for the sake of the weevils.

Sources

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. Viewed 20 Jan 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.

Kevin Shia

SW 2: The Biological Control in Lake Victoria: Was it Really that Effective?

With the proliferation of the water hyacinth in Lake Victoria, it is necessary to discuss aspects of biological control. The debate is to determine if biological controls help reduce the population of the Water Hyacinth in Lake Victoria. The biological factor consists of importing Neochetina weevils into the environment (Williams et al. 2007). The opposing argument is that the effects of El Niño are more significant in reducing the population of the plant. Wilson et al. (2007) believe that the weevils were the main cause for the decrease in the water hyacinth, while Williams et al. (2007) believes that El Niño was the main cause of the decrease in the invasive plant.

Wilson et al. (2007) state that the reason why the Neochetina larvae are so effective in damaging the water hyacinth mats is that they tunnel into the roots and cause massive damage to the whole plant. Wilson et al. (2007) also discredit Williams et al. (2007) by explaining how unlikely it is that the cloudy weather that is associated with the El Niño that occurred during the years of 1997 and 1998 can still affect the decrease of the water hyacinth between 1999 to 2000. They also state the claim that the data of Williams et al. (2007) cannot truly prove the relationship between the low light levels due to El Niño and the mortality of the plants because plants can still grow in low light. Wilson et al. (2007) claim that because the Neochetina population is an unstable host population, it can potentially lead to uncontrollable plant populations. They also claim that the weevils can also cause potential harm to themselves. For example, if the weevils cause enough damage to the water hyacinth, they can make the mats sink lower into the water, which can drown the eggs and larvae and the death of the weevils can proliferate the growth of the invasive plants again (Williams et al. 2007).

Based on the given information from Williams et al. (2007) and Wilson et al. (2007), I believe that both biological controls and the effects of El Niño helped change the total amount of water hyacinths in Lake Victoria. Even though the environmental effects of El Niño assisted with the reduction of the water hyacinth, I believe that the biological controls of the Neochetina weevils were more influential in reducing the growth of the water hyacinth.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria, http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 24 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Wather 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.

By: David Lung

Bio-control has been an inconsistent method of controlling invasive species. Often it results in failure and may even exacerbate the situation. For controlling water hyacinth, the water hyacinth weevils were introduced to stop water hyacinth from disrupting Lake Victoria’s ecosystem any further.

Wilson et al. believed that the weevils were the greatest factor in reducing the water hyacinth population and the El Niño event being a contributing factor. They have stated that water hyacinth populations have not increased (after sufficient time allowed for weevil growth) since the introduction of the weevils in 1995 and also that the weevils’ actions were the main cause of the reduction and eventual control of the weed’s population and the El Niño’s weather patterns made the finishing blow. The weevils’ actions opportunistically allowed other factors to cause further damage to it. They also stated that the weevil “represents the only control method that was implemented across the whole of the lake…” The El Niño event, herbicides and other control measures were temporary or concentrated means of control on the lake.

Willams et al. focused on the El Niño event being the main cause of water hyacinth decline and the weevils being a later factor. They asserted El Niño event was a widespread factor whereas other factors were not. They stated that the El Niño event’s reduction of light slowed down plant growth, allowing other factors such as weather patterns and weevil activity to control the weeds’ population. After the El Niño event in 1998, there was a drastic population decrease in the weed’s population. Also, they noted that in 2000-2001, the water hyacinth population increased despite the weevils’ actions. Willams et al. also stated that the population density of the weevils was still low up to 2002, asserting they were merely a contributing factor to the El Niño event.

Both groups make valid statements on the major cause of the control of water hyacinth, but I agree with Wilson et al. They don’t counter Wilson et al.’s statement that significant plant growth can occur in low light and also neglects that there is a predator-prey sort of relationship between the weevil and weed and also the weevil’s long growth period in explaining the weevil’s fluctuating population. The satellite images show bio control works to an extent, but controlling the nutrient level and researching more into the issue is needed, which is supported by both groups.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. Viewed 20 Jan 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.

(400 words without references)