Alien species introduction

Alien species are organisms that have been transported by human activity into regions where they have not historically been found. One of the most common means for species to become introduced or 'alien' is by through ship transport. As a ship's cargo is loaded and unloaded, the ship must accommodate changes in its weight and trim by taking on or discharging ballast water. For this purpose, ships use dedicated ballast water tanks, empty cargo or fuel tanks, or some combination of the three. However, many floral and faunal groups are drawn during ballast uptake. Due to the growth and survival unfavourable conditions in ballast tanks most of these organisms will die. Organisms that survive and are released into new habitats generally find a niche and become integrated into the biological community. However, a few have life cycle related qualities which, given the right environmental conditions, can make them a nuisance. The consequences of an exotic species in a new environment and becoming a 'pest' have been shown by toxin releasing dinoflagellates in Australian waters (and others) and comb jelly (Mnemiopsis leidyi) in the Black Sea for example. Toxic dinoflagellate species or their cysts can be transported in ships ballast tanks from one nation to another. Although the effects of many introduced aquatic species on habitats they colonise remain largely unknown, impacts include: decrease in abundance and even local extinction of native species, alteration of habitat structure, change in food webs, spread of diseases, social impacts, introduction of biological toxins, human health impacts and huge economic costs due to bio-fouling. For example, the US Congress has estimated that in order to combat zebra mussel invasion on a nation wide scale in the US, the costs to bear would reach US$ 3 billion over the next decade.

• Zebra Mussel: has clogged municipal and industrial water intake pipes and outcompeted native mussel populations in several major water bodies across North America. Also responsible for shellfish poisoning, and declining commercial and sport fisheries.
• A Strain of Cholera: responsible for paralytic shellfish poisoning, declining commercial and sport fisheries, and human disease. In humans, Bacterium Vibrio Cholera causes a viral illness of the small intestines, which results in diarrhea and possibly death.
• Japanese shore crab Hemi-grapus sanguineus: is now well-established and rapidly expanding along the Atlantic coast from Chesapeake Bay to Cape Cod.
• Black striped mussel: In 1999 the mussel was identified in dense aggregations at 2 marinas and one mooring basin in Darwin's harbour, located in Australia's Northern Territory. The black striped mussel is a species native of tropical to subtropical Atlantic waters from Columbia to the Gulf of Mexico. The species typically excludes most other native species, causing significant biodiversity losses at infested sites. In addition it leads to fouling of wharves and seawater systems. Besides Australia it has caused serious problems in ports in Singapore, Hong Kong, Japan and has reached pest proportions in India.

The most widely accepted method of ballast water management, is mid-ocean exchange of ballast water, typically at distances greater than 200 nautical miles from shore, and in water greater than 500 meters deep. Other methods such as ballast water treatment or dockside treatment are used only in special cases, or are currently in the research, development, or demonstration stages. However, exchange of ballast on high seas is time- consuming and cannot be performed in rough sea conditions. A Japanese corporation developed a recent promising technique. Originally aimed at reducing the level of corrosion the technique developed purges oxygen (reducing the corrosion of metallic structures) from ballast tanks with nitrogen gas. A study evaluating the benefits of this method for conservation purposes found that reduced oxygen level lead to an increase in the mortality rate of a number of invasive species' larvae.