Scientists have come up with a finding about the role of commercial ships in long-distance dispersal of micro-organisms including human, plant and animal pathogens. Researches from US show that global movement of ballast water, used for the stability of ships since the 19th century, creates a long-distance dispersal mechanism for micro-organisms as ships discharge large volumes of it at ports en route, according to a report in 'Nature'. Ports can receive relatively large volumes of ballast water. For instance, the US receives more than 79 million tonnes of ballast water from oversees each year. Ballast tanks carry a diverse community of organisms, resulting in many biological invasions. Pathogens, including those affecting humans are common in coastal waters and can also be transfered in ballast water. Researchers measured the concentrations of total bacteria, Virus-Like Particles (VLPs) and the bacteria vibrio cholera, which causes the human epidemic cholera, in the ballast water of vessels arriving at Chesapeake Bay, on the US east coast, from foreign ports. The samples revealed an average of about a billion bacteria and seven billion VLPs per litre – concentrations that exceed those reported from other taxonomic groups in ballast water by six to eight orders of magnitude.
Given that Chesapeake Bay received an estimated 10 billion litres of ballast water in 1991 alone, the measures indicate that ballast water probably delivers large numbers of microbial species and potential pathogens to this estuary, according to the report. Bureau Report