Aquatic species travel to distant, foreign habitats through a variety of different means. Some cling to the underside of marine vessels, others stow away in the ballasts of ships, while many are intentionally transported by humans for aquaculture, aquariums, or even as pets. While most non-native species are harmless, there are those that cause catastrophic ecological and economical problems, known as invasive species. Scientists believe that environments stressed by human disturbance are more vulnerable to invasive species.
Check out these 9 invasive species of the ocean, selected from the Global Invasive Species Database's 100 Of The World's Worst Invasive Alien Species.