Mnemiopsis leidyi was introduced in the black sea in the 1980s, where only one species of comb jelly, the small sea gooseberry occurred until then. The most likely cause of its introduction is accidentally by merchant ships’ ballast water. The first Black Sea record was in 1982.
By 1989, the Black Sea population had reached the highest level, with some 400 specimens per m³ of water (>10 animals/cubic foot) in optimal conditions.Afterwards, due to depletion of food stocks resulting in lower carrying capticity the population dropped somewhat.
It moved by ships by using the ballast, which the ship intakes water on the bottom making the ship heavier after dropping off goods to places, but when ships do this the tend to pick up animals along the way and carrying them to other places but this can be very bad because the other species that moved usually invade the natural habitat and can cause a lot of damage to the ecosystem.
to learn more about Canadian ecosystems, check out the link provided below!
> http://www.cbc.ca/news/technology/10-invasive-species-threatening-canadian-habitats-1.950951