"The introduction of invasive marine species into new environments, whether by ships' ballast water, attached to ships' hulls or via other means has been identified as one of the four main threats to the world's oceans, along with land-based sources of marine pollution, over-exploitation of living marine resources and the physical alteration or destruction of marine habitat. Increased trade and the consequent greater volumes of maritime traffic over the last few decades have served to fuel the problem. The effects in many areas of the world have been serious and significant. Quantitative data...