An alien species (also known as ‘exotic or nuisance species’) is the entry of any species into the ecology of which in the past it was not a part of. This species can travel to the new ecosystem from a neighboring ecosystem or from another part of the world. An alien species can cause damage or harm to animal, plant and human life thus completely disrupting the ecosystem. Two of the alien species that have seriously affected the other inhabitants of the ecosystem in the US and the other parts of North America include the Green crab and the zebra mussel.
In the home ecosystem, an alien species may not be able to thrive well due to the presence of certain factors such as diseases, presence competitors, lack of space, natural enemies, etc. However in the new ecosystem, the alien species is able to thrive uncontrollable due to the absence or restrictive factors. In the past, many alien species have been introduced into various environments. Some have entered due to human factors, whereas other may have entered due to certain natural factors.
Some species may have benefited the environment, which they are entered, whereas other may have seriously destroyed the native population. Invasion by alien species can have both, economic and environmental implications. The Zebra mussel is originally from the Caspian Sea and the Green crab is from Eastern Seaboard. These are classic examples of ‘Aquatic Nuisance Species’ (ANS) (ACS, 2007, MDNR, 2006 & NOAA, 2007). The Zebra mussels were identified in the Great Lakes and later spread to the other parts of North America via the major rivers and waterways.
They may have spread into the US from ships that have traveled through the freshwaters of Europe. They compete for plankton in the waters and in this way seriously jeopardize the food chain. They also damage parts of boats and ships. The Green crabs had spread into the San Francisco Bay region and later through California and Oregon States. They have a strong appetite for food in their territories and in this way deprive other organisms of food. The native crabs of US have seriously suffered from the invasion of the Green crab into their home territory (ACS, 2007, MDNR, 2006 & NOAA, 2007).