Ballast in ocean-going ships introduces harmful species and micro-organisms

The New Zealand screw shell (Maoricolpus roseus), introduced to Tasmania 70 years ago, has now successfully migrated north, establishing itself in vast beds in northern Bass Strait and off the coasts of eastern Tasmania, Victoria and New South Wales. Concerns over the impacts of the filter-feeding mollusc include its effects on native screw shell species and scallops, as well as for the shellfish-eating species and the rest of the food chains that depend on them.

“We are only just starting to understand the habits of this species,” says Dr Bax, an ecologist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Marine Research. “It is highly competitive with other species, and builds substantial beds to the detriment of other animals on the sea floor.”

“The concern is not simply some economic impact down the track,” says Bax. “We don’t know how far north it may travel, nor do we know how much it will alter the existing natural habitat and shut down the habitat of other species.”

“We’re not sure how it may have arrived here, but shipping trade at that time revolved around apples and timber, and ships came loaded with dry ballast that consisted of stones gathered from New Zealand shore,” said Bax.

Research published in the journal Nature this week, backs up the Australian fears, stating that discharges of ballast water by the world’s ocean-going ships “create a long-distance dispersal mechanism for human pathogens, and may be important in the worldwide distribution of micro-organisms as well as the epidemiology of waterborne diseases affecting plants and animals”. Impacts from introduced organisms sometimes have major impacts on the receiving ecosystem, say the researchers.

Though there is no reported evidence of outbreaks of human diseases from non-indigenous microbes in ballast water, according to the scientists, the findings indicate the need for much greater concern than has been shown so far.