There are a number of ways these invasive species reach their new ‘homes’. The primary way is that they hitch a ride to their new destination by boat; mainly in the ballast of cargo ships. A ballast is a large tank in the hull of a boat which is filled with sea water (and consequently a variety of different marine species) in order to counterbalance the weight of the cargo. The ballast is filled with water at the port of origin and released, along with all sea life within it, at its final destination.
Ocean pollution, especially plastic trash, guided by the currents offer these invaders a comfortable ride to far away marine ecosystems.
Sometimes aquarium owners may release their exotic aquatic pets into the wild without considering the consequences of doing so!
There are 3 possible outcomes for the these species in their new environment:
1) The new environment may prove to be too rough for the invader and they will quickly die off
2) The species will survive in its new environment with little impact to its surroundings
3) The newcomers can thrive and have a significant negative impact on the new environment
Generally, the new kids on the block (or on the reef) thrive in their new environment because their natural predators are missing. Thus, not controlling their population growth.
These alien species damage their new environment and harm their new neighbors by competing with them for food and/or space. They may also introduce diseases that their new marine community may not have any defenses against. This is comparable to when the Europeans invaded the New World and killed off large portions of the native population with diseases such as the common flu.
The Lionfish serves to exemplify the problem. It is originally native to the Indo-Pacific region but has been recently introduced by irresponsible aquarium owners into the coral and rocky reefs of the Atlantic. Without any natural predators in its new habitat its population has thrived. The Lionfish, with it poisonous spines, poses a threat to Atlantic marine life and divers alike!
The main area governments are focusing on is regulating the release of the ballast; either by having the cargo ships change the water along the way or treating it in order to kill its living content before the ballast is released. Furthermore, there is an attempt on the part of governments and other organizations to educate people about this problem which is destroying numerous marine ecosystems!