The final tally reveals the hotspots of bioinvasion. Large Asian ports such as Singapore and Hong Kong but also US ports like New York and Long Beach are among the sites of highest invasion probability. These waterways are notoriously busy, but, traffic is not the only important factor.
The North Sea, for example, does not rank among the top endangered regions despite intense shipping. Temperatures here are lower, making it more difficult for alien species to survive. However, arrivals from the other side of the Atlantic pose a serious threat to the North Sea. Most invaders are predicted to originate from the North American east coast.
Hanno Seebens from the University of Oldenburg said: "We also compared our model results to field data. And, indeed, most of the alien species actually do originate from there."
As severe as the risk of future invasions may be, the study also contains a hopeful message. If ship engineers could prevent at least some potential invaders from getting on board, the total invasion risk could be substantially mitigated.
By successfully removing a species from 25 per cent of the ballast tanks arriving at each port (eg with filters, chemicals or radiation), the overall invasion probability decreases by 56 per cent. The reduction is so disproportionately large because the effect of ballast water treatment multiplies at successive stopovers.
Bioinvasion is, as the researchers admit, a complex process, and records of past invasions are far from comprehensive. Facing these uncertainties, they simulated various different scenarios. Interestingly, the key results are comparable for different models, predicting the same hotspots and global highways of bioinvasion. The traffic on the main shipping routes plays the greatest role for the calculation.
Dr Michael Gastner, Lecturer in Engineering Mathem
|Contact: Joanne Fryer|
University of Bristol