It's estimated that nearly two-thirds of aquatic invasive species currently in the Great Lakes hitched a ride in the ballast water of cargo ships crossing the ocean.
That’s because ships take in ballast water at one port, often to help with stability, then discharge that water (and the organisms in it) at another port.
Species like zebra mussels, Quagga mussels and round gobies all made their way here in ballast water from ocean freighters, also known as "salties."
Salties’ ballast water is now regulated, with freighters required to rinse their ballast before entering the Great Lakes system. The move has helped dramatically slow the introduction of new invasive species to the lakes.
A helpful (tiny) glossary!
lakers (noun): Large cargo vessels that spend all their time within the Great Lakes.
salties (also a noun): Large vessels that travel on the ocean and come into the Great Lakes.
But the same isn’t true of lakers, or ships that move exclusively within the Great Lakes.
While the ballast water of these ships isn’t introducing new species, there’s a good chance it’s spreading invasive species throughout the lakes.
For example, one 2017 study sampled ballast water being discharged from lakers in ports on western Lake Superior. Scientists found five aquatic invasive species that hadn’t previously been reported in Superior.
But laker ballast water remains largely unregulated for logistical and financial reasons.
Years of research at the University of Wisconsin-Superior, along with other organizations, have focused on laker ballast water and potential ways to treat it.
But treating ballast from lakers faces different challenges than ocean freighters. For one, treatment can’t rely on the naturally sterilizing properties of saltwater. Plus, the cost of treatment is also a hurdle, especially considering how small the laker fleet is (only around 50 ships).
So developing technology to treat ballast water on lakers has been slow compared to ocean-going vessels.
And recent findings from the Lake Superior Research Institute at the University of Wisconsin-Superior could add another hiccup.
Research has mostly focused on larger, more active organisms being moved around in ballast water – fully-fledged zooplankton like invasive spiny water fleas.
“But nobody’s really addressed the reproductive stages,” said Matt TenEyck, director of the Lake Superior Research Institute. “[These organisms] all produce eggs of some sort, or some sort of resting stage. [Those], as well, could be taken up into the water and then moved around.”
Their study, which was published earlier this year in the Journal of Great Lakes Research, confirmed those suspicions.
“I think it’s tens of thousands … that we found,” TenEyck said.
Samples from the ballast water of lakers on Lakes Michigan, Huron and Erie scooped up lots of eggs and other more dormant, inactive life stages of these organisms.
Most of them were native species, or non-native and invasive species that are already well-established. But TenEyck says they're good models for potential new invasive organisms, who have similar eggs and resting stages.
“So the point behind that paper was to say, ‘Yep, they’re being moved. Now what?’” he said.
Now, scientists need to figure out if those tens of thousands of eggs and resting-stage animals are actually surviving the trip in ballast water. And when they arrive, are they able to hatch and live in their new environment?
“We think it’ll cause some risk to the receiving environment,” TenEyck said. “But we just, at this point, don’t know what that risk is.”
Determining that risk matters. It could help us better understand how microscopic invasives are being moved around by lakers.
But it would also give researchers more insight into what makes a ballast water treatment effective.
“By the time we’re done here now, in about four years, we hope to have a really good understanding of treatment technologies able to work in Great Lakes water,” TenEyck said. “And then maybe from there, a solution can be created.”
But it’ll be up to regulators to determine if those solutions are actually required.
Listen to IPR's Ellie Katz and Tyler Thompson discuss the new research in the audio player above.
