Ballast water: a source of biological pollution.

Byline: Dr. Afshan Yasmeen

Nature has a beautiful way of maintaining balance through food chain, ensuing in a stable ecosystem. A non-native organism, that does not have a well-defined place within the food chain, interrupts the existing ecosystem. Marine life is facing this kind of disaster due to invasion of foreign organisms through ballast water.

The world's oceans are threatened by marine pollution, overfishing, and physical destruction. As if it is not enough, they are also at risk from non-native, marine species migrating beyond their natural boundaries and are dispersed around the world via shipping.

Approximately two-thirds of traded goods worldwide are transported by ship. Large tanks in ships are filled and emptied with seawater in order to ensure the ship's buoyancy, stability, and maneuverability when the ship is loaded or unloaded. This ballast water in tanks is responsible for transporting thousands of specimens of native marine organisms including bacteria, small invertebrates, eggs, cysts, and larvae of various organisms.

It is estimated that almost 10 billion tonnes of ballast water are transported worldwide, with an average of 7,000 species per hour being transported per anum. This biological pollution is considered a second potential threat to natural biodiversity after habitat loss. The introduction of exotic species in the port area is currently a major environmental problem in various parts of the world and was first reported by the International Maritime Organization (IMO) in 1973 during the establishment of the international convention for the Prevention of Pollution from Ships- MARPOL 73/78.

Untreated ballast water releases species from one ecosystem to another. If the conditions of the new ecosystems are favorable. The species will thrive and become an invasive aquatic life form. They damage biodiversity and impact economic enterprises like agriculture, forestry, and fisheries. In the last two centuries, thousands of alien species have established in different parts of the world. Zebra mussel, green crab, and goby are examples of aquatic invasions through ballast water.

In North America, the introduced European Zebra Mussel has infested more than 40% of internal waterways and has cost more than US$5 billion in control measures. The invasion of species to non-native places has resulted in economic losses. The fishing industry has suffered the most as a result of species infestation in nonnative areas, where...