Researchers have been studying the paths taken by various marine alien species that are placing local ecosystems at risk. The invasive species are carried on the hulls of cargo ships or in their ballast water, which is continuously refilled and dumped when required.
Lionfish, killer algae and zebra mussels are just some of the marine animals that are threatening the ocean’s biodiversity. Larvae, bacteria and other microbes are also transported in the ballast water. Zebra mussels are particularly notorious – they reproduce extremely quickly and block water pipes, at one point even cutting off a town’s water supply in the US.
Scientists have found, however, that automatic invasion is not necessarily guaranteed – there is an optimal distance of around 8000-10000 km from homeland to new destination. Any less, and there is a chance that the species would be naturally occurring in that area anyway; any further, and it is likely that the specimens would not survive the journey.
Scientists from Germany and the UK have produced a mathematical model that will help marine biologists to calculate the probability of an alien species being able to establish itself at a subsequent port of call. The model was created using data gathered from almost three million cargo voyages that took place between 2007 and 2008. The ships carried identification systems, which allowed researchers to track them. The temperature, biogeography, ship size and shipping route were all factors that were taken into consideration when developing this important tool.
“It is called ecological roulette. The probability of winning from the perspective of the invader is really tiny – but because the number of attempts are now growing with more and bigger ships, you play this roulette so often that you become a likely winner sooner or later,” says Dr Michael Gastner, one of the scientists working on the project from the University of Bristol.
The research, published in the Journal Ecology Letters, created a list of the international ports that are at an increased risk of invasive marine species. Those ports situated in cooler waters do not have as much of a problem, since the exotic species can rarely survive in the colder temperatures. However, Singapore, the Suez Canal and Hong Kong are the top three ports most likely to succumb to alien species. The Panama Canal, Durban, New York and Los Angeles also make it onto the list, in addition to numerous shipping destinations in the Middle East and South East Asia.
One method of tackling this ecological problem is to treat the ballast water on ships before it is released back into the ocean. Scientists are still working on coming up with a more effective solution, however.
Dr Gastner is worried that economic pressures will deter shipping companies from taking additional measures, since the longer they spend in port, the more they pay. Time is, of course, money.
The International Maritime Organization, a special branch of the UN, is working on the development of ballast water management systems, and they may implement global standards for addressing this issue as soon as 2020.