Zebra mussels, an invasive species of freshwater clam identifiable by their brown and cream-coloured striped shell, were discovered this spring in a Minnesota lake that eventually flows into the Rainy River.
“They were discovered in Sand Lake and Little Sand Lake, which are about 100 km straight south of the Rainy River,” noted Ministry of Natural Resources’ biologist Chris Martin.
“It was a little more significant of a finding to us, locally, because those lakes do flow into the Rainy River≤” he said.
“The possibility of the species is a little greater in getting into our system than it used to be.”
The chance of zebra mussels making their way into Rainy River depends on a variety of factors, including the calcium levels in the lakes along the river system, as well as barriers to movement like dams.
“One of the things that we do have on our side is that zebra mussels require a certain amount of calcium in the water to form their shells, and a lot of lakes in this part of Ontario have fairly low calcium levels,” Martin explained.
“It may be less likely that they’re able to establish here.
“Suffice to say, there are a couple of lakes in this area that do have higher calcium levels and they’re at greater threat of being invaded,” he warned.
While the microscopic larvae would be unable to travel upstream into Rainy Lake, any water that is transported from the river to the lake could have a chance of spreading the mussels.
The larvae—or veligers—float freely for two or three weeks before they become too heavy and settle, then secreting sticky fibres, called byssal threads, to attach to hard surfaces.
The mussels then grow three-five cm long, and can live up to five years. Females can produce one million eggs per season.
The mussels, which are native to Russia, are believed to have invaded the Great Lakes originally in ballast water of ships.
“They seem to be in much lower numbers in Lake Superior, which is the closest Great Lake [to us], and it is believed one of the main reasons is because the calcium levels are quite low,” Martin said.
If the invasive species does make it to this area, however, the effects on the ecosystem will be major.
“If they were to become established, they compete with other fish and wildlife for food,” Martin explained.
“They are extremely effective in eating small plants like phytoplankton and zooplankton that float in the water column.”
Zebra mussels can filter up to one litre of water a day—removing the bottom of the food web which all aquatic life depends on.
“There’s a lot of other juvenile fish, minnows, and crustaceans that feed on those exact same food items,” Martin stressed.
“So basically they’d limit the amount of food for native species.”
If these native species die due to a lack of food, then larger species also will follow suit.
Less phytoplankton also means increased water clarity, which would drive light-sensitive fish to deeper depths while encouraging aquatic vegetation.
This, is turn, may have economic repercussions on the region’s fishing and tourism industries.
“They’re known to clog water intake pipes and they’re not pleasant to step on,” Martin added.
“Where you find huge numbers of them along shoreline, it makes it very difficult to get into the water,” he noted.
“They’ll even colonize along beaches, so pleasant places to swim will become difficult to access.”
Martin said zebra mussels also have been shown to attach in high numbers to our native clams, thus reducing their
There are steps that can be taken to prevent zebra mussels from spreading.
“[First], inspecting your boat and making sure your livewell is drained before you leave the system, or immediately after you pull your boat out of the water,” Martin said.
“And making sure you’re not transporting water anywhere else in your boat or bait bucket.”
Washing the outside of your boat can help, too, he added.
“The other important thing is to not release live bait because the water you collected from wherever it is you got your bait can have the younger zebra mussels in it,” Martin explained.
“They’re extremely small, they’re called veligers, and they float through the water column and move really big distances at that time.
“That’s what makes them so good at colonizing new areas,” he stressed.
“When they’re adults, they’re pretty sedentary,” he noted. “They sit in one spot for the rest of their lives.”
The same precautions should be taken to prevent other invasive species, such as the rusty crayfish and spiny water flea.
“The most important thing with zebra mussels is preventing them from arriving in the first place,” Martin reiterated.
He said the MNR is focusing most of its efforts on prevention.
“We’re working with the Minnesota Department of Natural Resources and the Ontario Federation of Anglers and Hunters; [and] with outreach programs to let people know about the threat of this invasive species,” Martin said.
“We have also got some volunteer monitoring programs where we ask the public to report any zebra mussels they see.
“It helps us keep tabs on where they are,” he explained. “We always appreciate when people provide us with information.”
If zebra mussels are found, people are asked to freeze them, then call the Invading Species Hotline at 1-800-563-7711.
In the unfortunate instance that a body of water becomes infected, the adult colonies are removed as best as possible and hopefully no new ones begin.
However, it usually is impossible to completely eradicate the species.
“Once you do have an invaded lake, make sure you are not transporting water or adults elsewhere,” stressed Martin.