Cargo ship. (Photo: Dr Michael Gastner/FIS)
Researchers shed light on bioinvasion via ballast water
Tuesday, May 07, 2013, 02:20 (GMT + 9)
Scientists from the Universities of Bristol, UK, and Oldenburg, Germany, have been studying the extent of the spread of potentially harmful invasive species through the ballast water of cargo ships. The researchers combed through ship traffic data and biological records to try to estimate the risk of future invasions.
Their findings are published in Ecology Letters.
Animals often hide as stowaways in the ballast tanks of ships or cling to the hull and, once they arrive at a new port, can drive native species to extinction, wreak havoc on whole ecosystems and impact the fishing and tourism industries. Conservationists and ship engineers are now trying to prevent the next big invasion, but data is lacking.
|Photo Credit: NOAA/IMO
For the research project, funded by the Volkswagen Foundation, the team gathered detailed logs of nearly three million ship voyages in 2007 and 2008.
“Our model combines information such as shipping routes, ship sizes, temperatures and biogeography to come up with local forecasts of invasion probabilities,” stated Professor Bernd Blasius from the University of Oldenburg.
Depending on the particular routes, researchers estimated the probability that a species would survive the trip and establish a population in subsequent ports of call.
"It is called ecological roulette," said Dr Michael Gastner from the University of Bristol, BBC reports. "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."
The team found that large ports such as Singapore, Hong Kong, New York and Long Beach are among the sites of highest invasion probability, in part due to being notoriously busy. The North American east coast sends many invaders to the North Sea, for example.
But there is hope. The team stated that it would make a big difference if ship engineers could prevent at least some potential invaders from latching on by removing a species from 25 per cent of the ballast tanks arriving at each port, the overall invasion probability falls by 56 per cent, because the effect of ballast water treatment multiplies at successive stopovers.
To grasp the uncertainties of bioinvasion, the researchers simulated various different scenarios, all of which predicted the same hotspots and global highways.
“Ship movements in the past few years are well documented, but there are many unknown [facts] about future trade routes,” Dr Gastner, Lecturer in Engineering Mathematics at the University of Bristol, added.
This is true when we look at Arctic passages, which thanks to global warming may become navigable for the first time in recent history. Future simulations will also have to take this into account as well as which engineering solutions for ballast water treatment will eventually be taken on by port authorities.
By Natalia Real