Researchers calculate the global highways of invasive marine species

University of Bristol press release: Globalisation, with its ever increasing demand for cargo transport, has inadvertently opened the flood gates for a new, silent invasion. New research has mapped the most detailed forecast to date for importing potentially harmful invasive species with the ballast water of cargo ships. Scientists from the Universities of Bristol, UK, and Oldenburg, Germany, have examined ship traffic data and biological records to assess the risk of future invasions.  Their research is published in the latest issue of Ecology Letters.

Animals and plants can hitch a ride on cargo ships, hiding as stowaways in the ballast tanks or clinging to the ship’s hull. Upon arrival in a new port, alien species can then wreak havoc in formerly pristine waters. These so-called invasive species can drive native species to extinction, modify whole ecosystems and impact human economy.

Some regions, such as the San Francisco Bay or Chesapeake Bay, have even reported several new exotic species per year. The knock-on effects to fishermen, farmers, tourism and industry create billions of US dollars in damage every year.  Conservationists and ship engineers are now trying to prevent the next big invasion. But without knowing when and where it may occur, their possibilities remain limited.

As part of the research project, funded by the Volkswagen Foundation, the team obtained detailed logs of nearly three million ship voyages in 2007 and 2008. Depending on the particular route travelled by each ship, the researchers estimated the probability that a species survives the journey and establishes a population in subsequent ports of call. Although this probability is tiny for any single voyage, the numbers quickly add up because modern cargo traffic volumes are enormous.

Professor Bernd Blasius from the University of Oldenburg and one of the researchers involved in the study, said: “Our model combines information such as shipping routes, ship sizes, temperatures and biogeography to come up with local forecasts of invasion probabilities.” 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 risk of marine bio-invasion caused by global shipping around the world. The brighter colour and thicker line indicates a higher bio-invasion risk  Image by Dr Michael Gastner