Aquatic Invasive Species

Wetlands 20, 280-299 (2000)

The spread of Phragmites australis, common reed, throughout Gulf and Atlantic Coast marshes has been virtually unstopped since its introduction in the late 1930’s. Because of Phragmites’ rapid spread, in areas such as the Chesapeake Bay, its current distribution and colonization rate is unknown. Dan Rice and colleagues at the University of Maryland used a geographic information system (GIS) to gain greater perspective into Phragmites distribution and colonization in three tidal freshwater and four brackish marshes in the upper Chesapeake Bay. Survey results indicated the presence of Phragmites at all seven sites. Using geometric growth formulas, rates of increase for each Phragmites stand were calculated. Older, more established stands have reached equilibrium while newer stands have increasing rates of growth. Rice et. al.’s results seem to suggest that there are limitations to the spread of Phragmites despite its prolific nature.

Estuaries and Coasts Vol. 30, p.469-481 (June 2007)

Phragmites australis (common reed) has caused devastating ecological disturbances to tidal marshes, particularly those in the Chesapeake Bay. Studies conducted on Phragmites abundance in the Chesapeake region are generally small-scale. Ryan King and colleagues at Baylor University performed a scaled-up study to determine the effects of urbanization on Phragmites abundance in wetlands in and adjacent to the Chesapeake Bay. By performing vegetation surveys over a large sample area accompanied by geographic and statistical analysis, King et. al. found that Phragmites abundance was markedly higher in areas with greater levels of both urban-suburban and agricultural development suggesting that development is “at least partially responsible for patterns of invasion across the Chesapeake Bay.” Salinity as well as geographic location may also play a role in determining Phragmites’ invasive success in the Chesapeake. The authors encourage further study of development, salinity, and geography in relation to Phragmites growth in coastal wetlands, as Phragmites invasion is indicative of irreversible ecological change in these wetlands.

Reading the four articles, especially the Mute Swans article, got me thinking about the definition of invasive species. While the ecological definition of invasive species is relatively well defined (“non-native species of plants or animals that out-compete native species in a specific habitat” from http://www.floridasprings.org/glossary.html), I feel that that the qualities that label a species as “invasive” and offensive by the public are much more vague.

The Mute Swans, for example, are scientifically an invasive species. The species was first introduced to the East Coast from Europe and Asia in the early 1900’s, when they were imported as decorative birds for parks and estates. Wild Mute Swan populations increased drastically in the Chesapeake Bay in the 1980’s and 90’s, as they out-competed native species for food and habitat. Legislation was passed in 2000 to control the swan population. There has, however, been public opposition to killing the mute swans. The article from class mentioned the “deeply divided” state panel, and the opposition from animal rights groups.

Mute swans pose just as great a threat to native species as snakeheads or didymo, but the opposition to swan population control in the Chesapeake made me wonder why there were no similar movements for these species. I guess the fact that swans are more aesthetically pleasing (as opposed to http://www.mountainmurmur.com/wp-content/uploads/2008/11/didymo-mararoa_s1.jpg) does influence public opinion on how comparatively “invasive” species seem, since noone wants didymo in their water. I’m sure there are many other invasive species that drastically disrupt native ecosystems and completely drive away certain species, but we don’t make a big deal about them because we are okay with having the invasive species around. There are factors (economic or aesthetic) other than endangering native ecosystems that the public takes into account when we decide whether a species is “invasive” and should be eliminated, or if nature should be allowed to run its course.

http://news.nationalgeographic.com/news/2003/06/0605_030605_muteswan.html

http://www.chesapeakebay.net/muteswan.aspx?menuitem=16930

With their elegant-shaped necks, and snowy white feathers, mute swans are arguably one of the most beautiful birds in America. Especially in the Chesapeake Bay, they have become a common vista for travelers and the inhabitants of that area. It is therefore surprising to find that the mute swans are an invasive species to the area and are on a warpath of destruction that is reaping havoc on the habitats of indigenous species. Mute swans were introduced to eastern United States when five “lawn-ornament” swans escaped from an estate. Since then, the population has bloomed from the original five to a peak of four thousand. The swans feed on shallow-root grasses that are the safe-haven for young crabs and fishes. Each swan can consume up to 8 pounds of bay grass each day, accumulating to 10.5 million pounds for the entire population. Also, mute swans are extremely territorial, and will trample over nests of endangered native bird species, e.g. least terns (Sterna antillarum) and black skimmers (Rynchops niger), etc.

Currently, measures are being taken to shoot down a quota of swans and addle their eggs with vegetable oil so that the eggs won’t be able to hatch. Though such dealings to appear to be a bit severe, they do appear to be necessary to control the mute swan’s exponentially expanding population. I think because of the extent to which muted swans have already disrupted the environment of native species, it is necessary to shoot down swans in attempts to control the population. However, because of how much mute swans have become part of the milieu in the Chesapeake Bay area, we should take caution from killing too many swans and from wiping them completely out of the area.

After all, what is an invasive species? All animals eventually will migrate from one place to another; the world is in a constant flux. Humans are merely facilitating the process. What difference is human-introduction of a species to a new area and natural migration? Over time, according to Darwin’s theory of evolution, the newly introduced will eventually adapt to the environment and become the indigenous. Therefore, though this isn’t what I actually believe, given Darwin’s theory of natural selection, is it even necessary to attempt to control the mute swans’ population? Maybe the endangered indigenous species are too evolutionarily weak and the swans are there to place a stressor on them so that they can evolve into a stronger species. But then that question doubts the concept that endangered species need saving.

http://news.nationalgeographic.com/news/2003/06/0605_030605_muteswan.html

http://www.njaudubon.org/SectionConservation/ThreatenedandEndangeredSpecies.aspx

http://www.washingtonpost.com/wp-dyn/content/article/2009/05/15/AR2009051501258.html

http://somd.com/news/headlines/2009/10085.shtml

Mute Swans and Trees of Heaven

Although many people see mute swans as majestic, beautiful creatures that add enjoyment to our lives, according to John R. Griffin, secretary of the Department of Natural Resources, they are “an environmental hazard to the Chesapeake Bay ecosystem.” Furthermore, other reports by Griffin’s appointees have continued to vividly depict the problem of mute swans by describing mute swans as “formidable threats.”

The mute swan or cygnus olor originated in north central Europe and north central Asia, and they spend their winters in North Africa, the Near East, and parts of India and Korea. The name, mute swan, comes from the fact that these swans are generally more silent than other swans. The mute swan was first introduced into North America in the late 1800s mostly for superficial reasons. Their population has grown dramatically over time not only in the Chesapeake Bay area but across North America including the Great Lakes region. Many environmentalists are worried because of their aggressive behavior towards other birds like Canada geese and even humans. Furthermore, they consume significant portions of vegetation in the areas in which they habitat, up to eight pounds of bay grass a day. In recent years, there have been many environmental actions concerning the mute swan both for decreasing the population as well as protecting them. There has been a significant amount of lethal action from 2000 on. The population of mute swans in the Chesapeake Bay went from about 4,000 in 2000 to only 500 in 2009. The Humane Society has spoken publicly against this awful treatment of animals on numerous occasions. Mute swans are protected in some areas of the country like Connecticut. I definitely do not think that anyone should be killing mute swans; I think that since we were the ones that brought them over here then we should find a way to deal with the problem efficiently in another manner. We should put them in wildlife reserves throughout the country or put them in areas that protect mute swans. If neither of these options work, then we should send them back to Europe or Asia. Maybe, we could give them as gifts to other countries and better political ties with other countries.

In Georgia, there are numerous types of invasive species such as mimosa, small carpgrass, honey bee mite, amber snail, as well as tree of heaven. A tree of heaven is usually a small tree that grows very rapidly. They are native to Asia and were first introduced to North America in 1748. They were typically planted in communities or cities due to the fact that they could easily grow in harsher conditions. Flowering happens in early summer, and they are very resilient growing in poor soil conditions as well as even in cracks in short structures or cement sidewalks. Trees of heaven typically do best in the edges of forests. The problem is that they displace native species and rapidly take over fields, meadows, and harvested forests. I am not sure what exactly has been done to help prevent these trees from continuing to populate, but once again like the mute swans, I think that humans must take responsibility for creating these situations for invasive species to cause environmental problems due to our introduction of foreign species into North America.

References

www.gainvasivespecies.org

http://en.wikipedia.org/wiki/Mute_Swan

http//:animaldiversity.ummz.umich.edu/site/accounts/information/Cygnus_olor.html