Hitching a ride - compromising the earth's waterways and ocean ecosystems

Container ship in port

The movement of ocean and water organisms around the globe as a result of hitching a ride on the ships traversing the seas is not a new problem nor is it one which the general public have not heard about. However the scale, extent and failure to act when solutions actually exist, is almost certainly a fact which is not so well known. Cargo ships and tankers require ballast water to avoid capsizing mainly when offloading cargo but also when carrying lighter loads - the water is up taken in one port and often discharged in another port, thousands of kilometres away. A large ship can carry up to 60,000 tonnes of ballast and more than 7 billion tonnes of ballast water is transported around the world each year in which an estimated 7,000 different species of seeds spores, plankton, bacteria, eggs and larvae hitch a ride into new surroundings. The impacts can be dramatic with examples being the European zebra mussel arriving in the Great lakes of North America, Chinese mitten crabs in Europe, Asian Kelp in Southern Australia, Mediterranean mussels in Southern Africa and dinoflagellates spreading across the world (the sources of 'red tides'). The Mediterranean has 900 alien species which originated from ballast water.

Efforts have been made to reach an international agreement through the UN Convention on Ballast Water in 2004 which requires ships to install kits to eliminate biological hitchers in their ballast water. The International Maritime Organisation has certified 20 commercial treatment systems which will do the task utilising various combinations of biocides, electrolysis, heat, ozone, irradiation or filtration systems. However for the treaty to come into effect, requires at least 30 nations representing 35% of the world's merchant shipping tonnage.  To date ratification nations only account for 29%  with the well known 'flags of convenience' countries - Panama, Bahamas, Malta and Cyprus - avoiding the issue. Nor have the US, UK, Germany, Italy and Japan ratified the treaty. The cost of taking no action is both economic as well as environmental for the invading species can cause significant negative impact - the Black Sea was devastated and its commercial fishing destroyed by the comb jellyfish  whilst the European zebra mussel blocked irrigation channels and water pipes in North America costing billions of dollars of restoration work. Inaction therefore is not really an option.