Farrah Chan conducts fieldwork for her study of aquatic invasive species.Farrah Chan conducts fieldwork for her study of aquatic invasive species.

Getting here is more than half the battle for invasive species, study finds

Foreign species hoping to survive a trans-oceanic voyage prefer the fastest route from port to port, a new study by a UWindsor researcher has found.

Farrah Chan, a biologist at the Great Lakes Institute for Environmental Research, has determined that shipping routes matter to stowaways in the holds of vessels.

“The conditions in the ballast tanks are harsh. It is dark and you’re trapped in with your predators, and the tanks are coated in nasty antifouling paints,” says Dr. Chan. “So we found that the longer the voyage, the lower the survival rate.”

Canadian waters are vulnerable to invasive species that travel in the ballast water of ships. As each shipment is loaded and unloaded from port to port, the ship fills the ballast tanks with water to counteract the fluctuating weight. But it isn’t just water; there are a suite of flora and fauna that tag along.

The concern is if these species survive in abundance and get dropped off at the destination port, Canadian waters can end up with potentially problematic invasive species.

Chan tracked two common shipping routes: the trans-Atlantic route that carries goods from Europe to the east coast of Canada, and the trans-Pacific route that carries goods from Asia to Canada’s west coast.

The unwanted voyagers were measured as a whole community. Chan looked at the survival rate and abundance of species on a day-to-day basis as vessels cross the oceans, a huge advantage over most studies, which collect samples only at the end of the voyage.

“We can track how communities change over time during the voyage,” she says. “We can understand how non-indigenous species are moved around as well as what are the risk factors.”

Chan found the risk of introducing foreign species to Canadian ecosystems was far higher with shorter trans-Atlantic route than trans-Pacific ones, because species had a better chance of surviving the trip.

She also discovered that the major prevention method of exchanging ballast water in the middle of the ocean was not always effective. During the ballast exchange, the ships picked up new species and augmented some existing ones. This increased the risk of delivering a bigger abundance of some species, which in turn means a greater chance of their surviving in the new environment.

This pattern was observed only for specific groups of organisms. Chan says this is a potential problem for Canada’s ocean ports.

“This leads to a concern that ballast water exchange may not be as effective as we thought it would be in certain cases,” says Chan. “The global shipping community is close to ratifying a treaty that would require ballast water treatment, such as chlorine or UV light, be used to reduce or kill the species in the ballast water. We think this is a prudent move given our results.”

Chan successfully defended her PhD in October and her findings were recently published in the journal Proceedings of the Royal Society B. The study was funded by the Natural Sciences and Engineering Research Council through its Canadian Aquatic Invasive Species Network.