Available September through May in school library issues of Virginia Wildlife magazine or on the Web. Exotic species can arrive in an area by various means, either by intentional introduction or by accidental introduction such as escape from captivity. One of the more recent exotic species being closely watched is the imported red fire ant, an accidental that found its way to Alabama in the 1930's on a ship from Brazil. The ballast water of merchant ships is commonly implicated in the introduction of invasive aquatic species. The zebra mussel is a good example of this, introduced from Asia to the Great Lakes in 1986 and now slowly heading south and east through the major river systems.
Ships take on water in their home port for stability.
Many aquatic species, such as fish larvae, algae and shellfish are able to survive the transoceanic trip in this ballast. The ballast water is released into the new port, introducing a host of alien organisms. The exotic often has an advantage in the new environment because it may not encounter the usual predators and diseases that had previously kept its population in check. If an exotic species becomes established, its population can create pressure on the native wildlife population by introducing new diseases and by competing for suitable reproductive sites, food, and other habitat requirements. On the other hand, it should be noted that not all non-native introductions are necessarily harmful.