Just about every sea-going vessel must have ballast water for stabilizing the ship. This seawater is discharged in the harbour where it docks or in its coastal waters. Every year, the transportation of around 10 billion tons of 'foreign seawater' occurs in the world seas. The North Sea is no exception. Here, too, ballast water is taken in and discharged.
Many different species of plants and animals from one sea region are transported to other regions via this ballast water. This transportation over large distances creates a tremendous disruption in the biodiversity of the place where the ballastwater is discharged, leading to significant ecological and economical damage.
Between 1900 and 2000, more than 150 introduced species were discovered in the North Sea, including various dinoflagellates, Japanese sargassum, American piddocks, American razor shells, Pacific oysters and the worm Marenzelleria. Some of these species were consciously brought here while others were imported by accident, for example along with a cargo of shellfish. However, many species traveled as stowaways in ballast water of ships.
In 2006, marine biologists suddenly found a large amount of the American sea gooseberry Mnemiopsis leidyi (known as the warty comb jelly or the sea walnut) in the delta waters and the Wadden Sea. This American sea gooseberry can develop explosively. Because they eat fish larvae and eggs, this kind of explosions can form a threat for the marine ecosystem. Earlier invasions in the Black Sea and the Caspian Sea produced tremendous problems. These problems have as yet not occurred in the Netherlands.
The problem with the introduction via ballast water is difficult to solve. One assumes that by changing the ballast water halfway along the voyage, in open sea, would decline the risk of carrying the organisms. Oceanic organisms would not survive well in coastal waters. This method has as advantage that one does not have to adapt the ships. Many countries even require the change of ballast water through law as a solution to the problem. Studies of methods for judging how clean ballast water is are being performed at the NIOZ.
A disadvantage of the 'change' method is that it is still not known whether or not it is effective. Sterilizing the ballast water is a certainty, however is more expensive and demands adaptations to the ships.
Another solution would be 'ballast-less' ships. This ship would have to be sea-worthy when loaded as well as unloaded. This solution has a additional advantage that it would use less fuel when traveling unloaded. However, such a ship does not yet exist. In October 2003, the organization Nederland Maritime Land issued a design competition for a ballast-less ship. The winner was the MonoMaran, designed by the MARIN bureau. This cleverly designed ship resembles a catamaran from underneath, but otherwise looks like a normal ship. It has a large draft when lightly loaded and a normal draft with a large load. There is more resistance but that is decreased with 'air oil', whereby air bubbles are blown under the ship. Another design was a ballast flow-through system, whereby the ballast water is continually flowing through the ship.
