Invasive species
An Invasive species is an animal that is introduced and adversely affects the ecosystem. An example of this is The European Green Crab which is an invasive species that was first discovered in the shores of Washington in 1998. The Green crab comes from Europe and an invasive species there is the Chinese Mitten Crab. It was first discovered in 1995 when residents of Greenwich saw it coming out of the River Thames.
How The European Green Crab got here
The European Green Crab first came to America in 1988. The reason it came was because when large ships go out to sea they carry ballast water to stay stable when out in open ocean. When ships dock they empty and change the ballast water. When the ships change water the crab escaped and found a new home on the East Coast.