Ship ballast water contaminating marine environment
Clockwise from top: Discharge of ballast water from a container ship. Sea lamprey Petromyzon marinus (shown attached to a lake trout) led to the collapse of lake trout (Salvelinus namaycush) populations in the Great Lakes during the mid-20th century (Photo: U.S Fish & Wildlife Service ). A cluster of zebra mussels on a small rock ( Photo:J. Ellen Marsden, Lake Michigan Biological Station ) .
Ballast water of ships may be the source of the largest volume of foreign organisms released on a daily basis into the marine ecosystems. The ballast water has been a primary method of alien species introduction throughout the world. Scientists estimate that as many as 3,000 alien species per day are transported in ships around the world. The introduction and spread of alien invasive species is a serious problem that has ecological, economic, health and environmental impacts, including loss of native biological diversity. What is ballast?Ballast is defined as any solid or liquid that is brought on board a vessel to increase the draft, to change the trim, to regulate the stability or to maintain stress loads within acceptable limits. Prior to the 1880s, ships used solid ballast materials such as rocks and sand, which had to be manually shovelled into cargo holds, and similarly discharged when cargo was to be loaded on board. If not properly secured, solid ballast was prone to shifting in heavy seas causing instability. With the introduction of steel-hulled vessels and pumping technology, water became the ballast of choice. Water can be easily pumped in and out of ballast tanks, requires little manpower, little cost and as long as tanks are kept full, poses little to no stability problems. What is ballast water?
Ballast water is fresh, brackish or marine water that has intentionally been brought on board to adjust the ship's stability. Large ships often carry millions of gallons of ballast water. This water is taken from coastal port areas and transported with the ship to the next port of call where the water may be discharged or exchanged. Organisms ranging in size from viruses to 12 inch fish living in the surrounding water or sediments are taken on board with ballast water. Most ships are equipped with a range of ballast capabilities and capacities, but generally it is 25 to 30 per cent of their dead weight tonnage. Why is ballast water an issue?
Coastal port areas are home to a wide variety of organisms that live in the water and bottom sediments. If a ship takes on ballast water in a shallow area, sediments and any associated organisms may be pumped into ballast tanks. When ballast water is released, these organisms may also be released. The discharge of ballast water may cause the introduction of alien species which threaten the ecological balance of the surrounding sea and thereby represent a direct threat to biodiversity. There are many aquatic species that may be carried in ship's ballast water, including bacteria, viruses and other microbes, micro-algae, and various life stages of aquatic plant and animal species. Species are considered alien if they are not native to a given ecosystem. These introduced alien species, or bioinvaders, are also referred to as exotic species, non-native and non-indigenous species. Alien species are considered to be invasive when their introduction causes, or is likely to cause, harm to the environment, the economy, or human health. At present, we can not predict which organisms will die during a long journey in a ballast tank or why some are still alive when ballast water is released. Larger organisms often survive the journey by eating smaller ones. When faced with unfavourable conditions, some microorganisms and plankton species will form spores or other tough outer coverings for protection. As a spore, an organism may survive for a long time without food or in a different salinity or temperature than its natural environment. Once the environment becomes favourable again, such as when they are discharged into a port, the organism may change back to its active form. As said, scientists estimate that as many as 3,000 alien species per day are transported in ships around the world; however, not all transported species survive the trip and their new home or surroundings because temperature, food, and salinity are less than optimal; but, the few that do survive and establish a population have the potential to cause ecological and economic harm. These bioinvaders can cause disruptions in the natural ecosystem, economic troubles, and even carry human diseases or introduce new genetic materials which not only induce mutation in native marine organisms but also jeopardize their natural abilities. Ecological impact
The introduction and spread of alien species into any ecosystem is highly undesirable because of the negative and irreversible changes that can result. Alien species with no natural predators can wipe out native species by altering their habitat, feeding on them excessively, or by using up a particular food source on which native species depend. Zebra mussels are a major threat to endangered North American freshwater unionods, such as the quagga mussel (Dreissena bugensis) by competing for food and encrusting their shells, resulting in mortality. Six countries near the Black Sea have been affected by the Atlantic comb jelly. It has eliminated the zooplankton in the Black Sea which has exhausted the region's anchovy fishery. Shellfish in Tasmania have been wiped out by North Pacific sea stars. Economic impact
Until the introduction of sea lamprey (Petromyzon marinus) to the Great Lakes in 1955, there was no general understanding that alien species could be both an environmental and an economic problem. Sea lampreys have decimated lake trout, whitefish and chub populations in the Great Lakes resulting in severe losses to the Great Lakes' recreational and commercial fisheries. The Great Lakes Fishery Commission reported that sea lamprey control, assessment and research cost $13.5 million in 2001. Once the European zebra mussel introduced to Lake St. Clair in the early 1980s, zebra mussels quickly expanded their range throughout the Great Lakes and caused billions of dollars of damage. Zebra mussels have caused tremendous problems for industrial raw water users by clogging water intake pipes resulting in significant increases in annual operating costs to the automotive industry, water purification plants, and electric power utilities. Periodically these organisms need to be removed from pipes and other structures which requires time, money, and possibly specialised equipment. The cost to keep the water intake pipes at Ontario(in Canada) Power Generation facilities clear of zebra mussels from 1990 to 2000 was estimated at close to $44 million. The total estimated impact on industries, businesses and communities is over $5 billion in monetary term. Environmental and human health impact
Alien species can also destroy the environment and threaten human health and safety. For example, the Chinese mitten crab (Eriocheir sinensis), which is able to live in both fresh and salt water, was found in the lower St. Lawrence River in 2004. They can travel hundreds of miles through inland waterways and reproduce in enormous numbers, burrowing into riverbanks and causing soil erosion and destruction of levees. The crabs are a danger to human health because they are a host of the oriental lung fluke (Paragonimus westermani), a parasite that can penetrate the skin or be ingested and can cause severe illness in humans and other mammals. Through their filtering activity, zebra mussels take in hazardous compounds such as polychlorinated biphenyls (PCBs). Fish and waterfowl that eat the mussels carry those poisons into the food chain. Some species introduced to new places through ballast water contaminate filter feeding shellfish, making them toxic and inedible. Consumption of these contaminated shellfish by humans can cause severe health problems and even death. Moreover, harmful microorganisms of various types can become more virulent as a result of contact with other organisms in ballast water. Ballast water can also transport cholera around the world. In 1991 the South American cholera epidemic was a result of the cacterium discovered in oysters and fish in Mobile Bay, Alabama. 1/3 of the ships arriving from South America in Alabama carried this bacterium. Conclusion
Marine pollution from ship ballast water is one of the greatest threats to ocean life. Ballast water is one of the major pathways for the introduction of non-indigenous marine species. Because of the potential for ecological and economic damage posed by these organisms, ballast water should be managed to minimise the risk of species introduction.
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