Non-indigenous or invasive species can be dangerous because they can outcompete native species for resources, leading to declines in native populations. They can also introduce diseases or parasites that native species have no immunity to. In addition, they can alter ecosystem processes and disrupt food webs, leading to a cascade of negative effects on other species. In some cases, invasive species can even cause the extinction of native species. It also can cause economic loss as well because some species can damage crops and also harm infrastructure.
There are many non-indigenous species that have been transferred from port to port via the merchant fleet, and many of these species have become invasive and cause significant harm to native ecosystems. Some examples include:
- Zebra mussel: native to freshwaters in Europe and Asia, it was accidentally introduced to the Great Lakes in the 1980s through the ballast water of cargo ships. It quickly spread and now infests waters throughout North America, clogging water intake pipes and out-competing native mussels.
- Asian carp: native to Asia, it was introduced to the United States in the 1970s to control aquatic vegetation in fish farms. It has since escaped into the wild and has spread throughout the Mississippi River basin, threatening native fish populations.
- European rabbit: introduced to Australia in the 1800s for hunting, the rabbit population quickly grew out of control and has caused extensive damage to native vegetation and ecosystems.
- Burmese python: native to Southeast Asia, has been introduced to Florida, USA, and now poses a significant threat to native wildlife, and it also can cause an impact on the Everglades ecosystem.
- Cane toad: Native to Central and South America, cane toads were intentionally introduced to Australia in 1935 to control sugarcane pests, but they spread quickly and have had a devastating impact on native Australian wildlife.
These are just a few examples, but there are many other invasive species that have been transported through shipping and have caused harm to native ecosystems.