When it comes to invasion from foreign species, not all ports are created equal, according to a new study that tracked 2.89 million shipping voyages.
The goal was to map the ports and routes most likely to carry invasive species hitching a ride in ships’ ballast water, which is drained or pumped in at ports to balance a ship’s changing cargo load. When non-native plants and animals arrive in a new ecosystem, they can cause billions of dollars in damage and create ecological disasters.
“It’s ecological roulette,” says Hanno Seebens, a biologist at the University of Oldenburg in Germany and the study’s lead author. “There’s only a small probability that an individual species can successfully invade on a single voyage, but if you do this thousands of times, then you will see species establish themselves.”
The new work in Ecology Letters provides an unprecedented map of the ports and shipping channels that invasive species use the most — what Seebens calls the “highways” of ship travel most likely to lead to an invasion.
These equatorial ports have warm water and plenty of cargo ships, putting them at high risk of exchanging invading species.
The black striped mussel, for example, first made its way from the Caribbean to the Pacific by attaching to ships’ hulls and sailing through the canal, built in 1915. The mussel colonized Indian ports by the 1960s, hit Japan in the ‘70s and started taking over in Hong Kong’s harbor by 1980. The mussel’s speedy growth and salt tolerance make it a master invader and a major nuisance.
This is the U.S. port at highest risk of invasion from marine shipping, with around 5,000 container ships, oil tankers and other vessels arriving annually from all over the world.
Ships arriving from multiple European ports at similar latitudes elevate the threat of invasive species.
The Arctic is unlikely to host invasive species, due to its freezing climes.
But as global warming melts Arctic ice, new shipping routes may open up in the coming decades that could allow new patterns of invasion to take shape.
With 50 ships traveling through the canal daily, swapping around 10 million tons of ballast water annually between the Indian Ocean and the Mediterranean, it’s no surprise the Suez is a hotbed for species invasion.
Since it opened in 1869, the canal has ushered more than 300 species through its waters, the most recent being an Indo-Pacific marble shrimp. Scientists reported spotting the shrimp off the Israeli coast late last fall after they traveled through the canal.
A ship arrives or departs Singapore’s harbor every couple of minutes. As a hub for local Asian shipping and global transport, this island city-state is not just the world’s busiest port, it’s also at the greatest risk of invasion by non-native species.
Because many ships arriving in Singapore come from climates with similar conditions, critters that make their way into the port stand a good chance of surviving. Although a few mollusks have come to Singapore as stowaways on ships, invasives are not currently a problem to Singapore.
That doesn’t mean that they won’t cause havoc in the future.
Frequent shipping between these two ports — over 250 ships a year — combined with their similar climates, means the ports are likely to trade non-native species along with the ships’ cargo.
Although no invasive species have been identified yet, Seebens says it’s just a matter of time until a hitchhiker takes advantage of this marine superhighway.
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