The UN lists "invasive species" dispersed by ballast water discharges as one of the four main threats to the world's marine ecosystems. The findings will appear in the journal Environmental Science and Technology.
Shipping moves more than 80% of the world's commodities and transfers up to five billion tonnes of ballast water internationally each year, data from the UN shows. Vessels, especially large cargo tankers, need ballast tanks to provide stability in the water and correct any shift in the ships’ mass. When a ship's cargo is unloaded, it fills with ballast water; when it is later reloaded, often on the other side of the world, the water is discharged. Co-author Dorin Boldor, from
…For thousands of years, marine species have been dispersed throughout the oceans by natural means, such as currents and drifting on debris. But natural barriers, such as temperature differences and land masses, have limited the range of some species' dispersal and allowed different marine ecosystems to evolve.
Since the emergence of the modern shipping fleet and growing trade between nations, these natural barriers have been broken down, allowing the introduction of alien species that upset the equilibrium of ecosystems. The UN-led Global Ballast Water Management Programme (GloBallast) estimates that at least 7,000 species are able to be carried across the globe in ships' ballast tanks….All sorts of critters in the bilge. Shown here, the stern of the giant container ship Colombo Express, shot by Danny Cornelissen, from the portpictures.nl website, via Wikimedia Commons