Oct
31
Filed Under (SW10) by Natalie Ferguson on 31-10-2010

In 1998, Edward P. Levri from Indiana University studied the how effects the parasite Microphallus has on the behavior of New Zealand mud snails impacts the New Zealand fish, Potamopyrgus antipodavun. The design of his experiment included collecting fish samples from various hours of the day, particularly morning versus evening, and counting the number of infected snails compared to non infected snails. He was able to count the snails present in the fish by first killing them and then examining the guts. Levri found that the fish guts tended to have a significantly higher amount of uninfected snails than infected. These results showed that the behavioral changes the parasite caused the snail made the fish less likely to be in the water during times where the fish population was feeding. These findings show that the parasite does not have a secondary impact on the New Zealand fish.

Oikos 81, 531-537 (1998).

Entomophaga 30(3): 279-286

Biological control using the Cyrtobagous salviniae weevil is a popular control method for giant salvinia. Both the effectiveness of biocontrol and the growth rate of the plant are reliant on environmental conditions such as nitrogen levels and temperature.

Forno and Bourne (1985) examined how temperature, nitrogen content of the plant, and density of weevils altered the effectiveness of the weevil. The results showed that high-density populations of weevils (4 adults/bud) at high temperatures had significant damage to the plant. However, plants with low-density populations (1 adult/bud) developed buds faster than control plants with no insects. Varying nitrogen levels in plant tissue, however, did not influence plant development. The study suggested that high temperatures and high population density is the weevil are more important for reducing giant salvinia growth than a high nitrogen content.

Sep
24
Filed Under (SW5) by Tyler Lacy on 24-09-2010

Biological Conservation 102, 331-341 (2002)

Aquatic invasive species can have devastating effects on the ecosystems they invade. It is well known that many invasive species are transported long distances to foreign environments in ship ballast water. Experiments on the deoxygenation of ballast water suggest that the process could not only lower survivorship of species in the ballast water but also prove cost effective for the ships by lowering the rust levels of ballast tanks.

Mario Tamburri of the Monterey Bay Aquarium Research Institute and his colleagues tested the survivorship of  aquatic organisms as well as rust accumulations in oxygenated water vs. deoxygenated water in ballast tanks. They found that rust levels of the deoxygenated water were far less than the oxygenated water and they observed a significant mortality in the deoxygenated water in just a few days. Deoxygenation systems in ships may offer a financial incentive to ship owners as well as significantly reducing the number of aquatic species they transport.

Sep
13
Filed Under (SW3) by Haley Ishimatsu on 13-09-2010

In Africa, Lake Victoria has been infested with water hyacinth for decades. Only recently, in the 1990s, people began to try and get rid of the invasive plant. One form of control was the release of weevils that ate and lived in the water hyacinth. This type of control using one species to rid of another is called bio-control. The introduction of weevils is widely thought as the main reason that the levels of the water hyacinth have been reduced and maintained at this lower level. However, two scientific papers, Wilson et al. (2007) and Williams et al. (2007) argue over this point. Williams et al. (2007) suggests that the bio-control wasn’t the only factor in reducing the amount of the water hyacinth. It says the the El Nino of 1997-1998 was a big factor on the control of the invasive plant. The low light levels may have caused the hyacinth to have slower growth and reproduction rates. In turn within several years, the effect of this would be apparent. Wilson et al. (2007) states that the low light levels could not have had a significant affect on the water hyacinth. It also says the the weevils have worked to infest most of the water hyacinth that is currently in the lake and are on their way to sink and destroy much of the plant.

Based on the information that was shown by Wilson et al. (2007) and Williams et al. (2007), it seems that the weevils and El Nino have played big roles in reducing the amount of water hyacinth. However, the document of how the weevils have been the main reason seems to have the more compelling evidence. In light of new images in recent years, there have been photos of Lake Victoria that suggests that the invasive water hyacinth is back in full force. This re-invasion implies that affects of bio-control can be unstable and temporary. The people who depend on the waters of Lake Victoria for food, water, and money can only hope that another way to control the water hyacinth can be found soon.

References:

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

Sep
13
Filed Under (SW3) by Blair Ballard on 13-09-2010

Don’t let water hyacinth’s deceivingly delicate appearance deceive you. According to NASA, water hyacinth is among the world’s most noxious invasive weeds.

In 1989, water hyacinth spread to Lake Victoria and by 1995, the problem got so severe that weevils (or Neochetina spp.) were brought in as biocontrol agents. Although a decline in water hyacinth was observed after the four years weevils typically take to come into effect, the severe weather conditions of the 1997-1998 El Niño introduced a debate as to whether the biocontrol agent, or the storm was truly responsible.

Wilson et al. (2007) argues that the reduction in water hyacinth was due to significant weevil damage and that the increased wave action and higher water levels of El Niño merely accelerated the process by causing further stress to plants already damaged by the weevils. In contrast, Williams et al. (2007) argues that the high water levels (1.7m higher during the storm) and increased wave action were the true driving force, effectively dislodging stands on the shoreline.

Throughout El Niño, cloudy conditions caused reduced light levels. Wilson et al. (2007) states that despite these diminished light levels, they were still sufficient for plant growth. Williams et al. (2007) disagrees by arguing that the reduced incident light caused by El Niño was likely to exert progressive wear on the growth and reproduction of water hyacinth, a photosynthetic plant.

In my opinion, both Williams et al and Wilson et al. offer compelling arguments, leading me to believe that the temporary eradication would not have been merely as successful had both the weevils and El Niño not played a role.

In 2005, a MODIS image shows Lake Victoria virtually clear of water hyacinth. A year later, however, after extremely heavy rainfall and increased nutrient-rich sediment flooding into the lake, a second MODIS image shows Lake Victoria once again infested with the invasive plant. This evidence shows that despite the short-term success of the weevil as biocontrol, the changing conditions of Lake Victoria (food supply, etc.) prevent weevils from being a long-term solution to the water hyacinth problem.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 12 Sept 2010.

William, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline accross Lake Victoria- Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94096.

Wilson, J. R. U., O. Ajounu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenshwander, S. E. 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.

Sep
12
Filed Under (Uncategorized) by Manuela Mejia on 12-09-2010

In Lake Victoria, an invasive species is covering the water’s surface with green mats and blocking plants underneath it from direct sunlight, causing their death and many other related problems such as decrease in water quality and spread of waterborne disease. This species, the water hyacinth, has been a great puzzle for scientists. The original method of biological control, weevils (or Neochetina spp.), were introduced to reduce the water hyacinth population in 1995. A sharp decline of water hyacinth in 1998 and 1999 and again in 2000 is attributed to the weevils’ destruction by Wilson et al. (2007). However, according to a rebuttal article from Williams et al. (2007), the weather patterns brought by El Niño in 1997 and 1998  were mostly responsible for the water hyacinth’s decline.

According to Wilson et al. (2007), it is apparent that weevils caused the decline of the water hyacinth population because after their introduction, they normally take about three to four years to act, consistent with their introduction in 1995 and the decline in 1998 and 1999. They also claim that the resurgence shown on their graph of Lake Victoria hyacinth levels in 2000 occurred simultaneously with a low weevil population.

In contrast, Williams et al. (2007) argue against the claims made in Wilson et al. (2007). An interesting fact cited by Williams et al. states that El Niño caused a 1.70 meter rise in Lake Victoria’s water levels, which led to stable shoreline stands of water hyacinth washing into the lake. This compelling evidence, as well as individualized graphs for each region of the lake and explanations of how low light levels from El Niño’s stormy effects combined with other factors, including biological control using weevils, reduced water hyacinth populations, solidify Williams et al.’s conclusions.

Considering MODIS satellite images from 2005 and 2006, the re-invasion of water hyacinth adds another piece to the puzzle. The NASA Earth Observatory (2007) states that the reappearance of the invasive species coincided with extremely heavy rains. Reexamining Wilson and Williams’ claims, it is clear that Williams et al.’s (2007) worries about stormy El Niño and cloud cover are relevant in this situation as well. In my opinion, this correlation of information between two sources in two different time frames shines in favor of Williams’ argument. Also, Williams et al. (2007) use more area-specific graphs which seem to more accurately depict the water hyacinth problem. I agree with Wilson et al. (2007) that biological control is essential in controlling the water hyacinth invasion, but Williams et al. (2007) present more convincing data. Hopefully, we will be able to find the ideal balance and solution to maintain control in Lake Victoria.

References:

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

Sep
11
Filed Under (SW3) by Stefan Cafaro on 11-09-2010

In the 1980s a new invasive species, known as the water hyacinth, was introduced to Lake Victoria. This exotic plant was able to successfully plant its roots in its new home and thus the population of water hyacinth sky rocketed. In order to combat this alien vegetation, the weevil, which feeds on the hyacinth, was introduced into the area.

By 1998 a significant decrease in the hyacinth population was observed. Based on this information one could easily conclude that the weevils seemed to be responsible for the eradication of the water hyacinth. That is the opinion of John R.U Wilson et al. (2007), who in his scientific article, published in the journal Aquatic Botany, expressed his firm belief that the weevil was the main factor contributing to the decline of the hyacinth. However, for Adrian E. Williams, this conclusion was not as cut in stone as it appeared to be. In Williams’ et al. (2007) article published in the journal, Aquatic Botany, he attributes the rapid decline of the hyacinth population in 1998 to the presence of an El Niño (a climate pattern exhibiting high pressure, warmer temperatures, and extreme weather.) Both Williams and Wilson illustrate their opinions through their analysis of a variety of experiments and collections of data however, Williams et al (2007) thoroughly considers Wilson’s data and draws significant attention to the population spikes that happened in the exact years of the El Niño event. In doing so, Williams et al(2007) presents a strong case for the impact of the El Niño that Wilson can do little to disparage.

In more recent years, an article titled “Water Hyacinth Reinvades Lake Victoria” was released by NASA which illustrated the reemergence of this invasive plant into the area despite the efforts of the weevil. This article seems to give more support to the argument made by Williams as well as indicating the possible need to find alternative methods of eradicating the water hyacinth from Lake Victoria.

While no answer currently exists to this debate, I believe that Williams does a better job of analyzing the spikes in both the growth and decline of the hyacinth population and illustrating their significance in correlation with the El Niño event that occurred in 1998. He explains that while the weevil has been successful at halting the exponential growth of the hyacinth, the extremely wet and cloudy conditions brought by the El Niño definitely had a colossal impact.

References

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria.

http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. 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.

Revision Strategy

In order to revise my SW3 post, I decided to utilize each of the three suggestions that I was given in the comment section of my blog. I agree with Cole who stated that I should switch around the order of my third and fourth paragraphs. Doing so seems to make the arguments presented in my paper connect in a more logical manner. I also tried to add in a few more details supporting why I believe Williams et al(2007) presented the stronger argument while also trying to stay within my word limit.

Sep
08
Filed Under (SW2) by Stefan Cafaro on 08-09-2010

Invasive species is currently one of the most threatening problems in today’s world to both the environment and to national economies. Even though a majority of people probably do not realize the extent to which this problem has elevated, the consequences are continuously multiplying around the world.

National Geographic’s documentary, “Strange Days on Planet Earth”, tries to shed light on the mysteries and issues posed by numerous invasive species across the globe. Edward Norton expertly narrates the story behind the countless alien species that have wreaked havoc in many ecosystems.  The film discusses the indicators and the effects that invasive animals have on their new homes and the native species who reside in them. The main consequences of this issue include increases in outbreaks of disease, famine, and the extinction of native species. This documentary also explains how humans have contributed a massive amount to the feasibility of one species traveling to other environments. While most invasive species are not able to sustain themselves in new places, this film highlights a few examples of successful invasive species; that is successful in both surviving and destroying the previous structure of that particular area.  These examples include the termites of New Orleans, the zebra mussel, and the Mediterranean fruit fly; each of which have caused billions of dollars worth of damage. While most invasive species, once settled into their new homes, are very difficult to eradicate, Strange Days on Planet Earth does a great job of illustrating the methods that people are using to try to control and eliminate these animals.  For example, the water hyacinth, an invasive plant native to South America, had begun to completely take over Lake Victoria. The populations of hyacinth has since then been greatly reduced due to the introduction of the weevil (herbivorous beetles native to North America) into the lake. This method of introducing a new predator to get rid of an invasive species is referred to as bio control.

Overall, this documentary successfully portrays the potential catastrophic effects that invasive species can have around the world as well as the actions people are taking in an effort to slow and even reverse these effects. The film also leaves the viewer with the notion that these isolated problems being posed by invasive species may just be a warning for the most massive extinction on planet earth since the age of the dinosaurs; a message that is sure to resonate in the viewers’ mind well after the documentary’s conclusion.