Zebra mussels flex reach, threaten northern Lake Winnipeg and Manitoba Hydro stations

The zebra mussels that have invaded Lake Winnipeg might actually do some good for the southern end of the lake, but the north basinmight not be so luckyand that means impacts to the fishing industry and Manitoba Hydro, says a research scientist.

Other than a frightful and potentially painfulpile of sharp-edged shells washing up in the spring, beachgoersin the south basin of the lake might not even notice much of a change.

"The concerns are all over the map about what's going to happen to the lake. We've heard everything from zebra mussels won't have a big impact on the laketo the lake is dead," said Scott Higgins, research scientist with the International Institute for Sustainable Development's Experimental Lakes Area, southeast ofKenora, Ont.

"I've seen the full range of comments on that. It's obvious there is some uncertainty there."

The invasive species is a filter feeder, siftinglarge amounts of plankton and other microscopicdetritus from the water and devouring that material.

"In many lakes they've shown toclear up particulates in the water, reduce the amount of algaeand make water clarity higher," saidHiggins, adding that each mussel canfilter as much as one litre of water every day.

May reduce algal blooms

Multiply that by millions of mussels and that's a big impact.

"In some ways, it's a good thing. Maybe it will reduce algal blooms," Higgins said. "But there's always a concern when mussels are really effective at doing this because algae represents the base of the food web.

"If the base of the food web significantly declines, there is concern those effects may move up the food web toinvertebrates, which also feedon that algae, and ultimately to the fish community, which feeds on those invertebrates."

In small or shallow lakes and rivers, that can be devastating to the entire ecosystem. In bodies of water like that,the mussels can filter the equivalent of the entire volume of water in the lake in just a couple of days, Higgins said.

"But in a really large lake, like Lake Winnipeg, that's simply not feasible, at least not in the south basin," he said.

That's because that part of the lake is filled with too much loose sedimentto become overrun by mussels. That sediment gets stirred up in windstorms and the mussels don't like that, Higgins said.

They grow attached to hard surfaces rocks, docks, boats. They can also grow on aquatic plants and consolidated sediment, which isrock made from materials that have been cemented togetherlike sandstone.

"What this all means is they are likely to be restricted to the edges of the lake, where there are rocky shores and docks," he said.

So inbeach areas, you may find a rock or some boulders and docks withzebra mussels but that's about it, aside from the spring piles.

Those are due to mussels dying off naturally,during winter, or from getting crushed by the thick ice. In spring all those shells get washed onto the beach, Higgins said.

"But I don't see any evidence so far that zebra mussels are going to colonize the middle of the southern basin to any great extent," he said.

And zebra mussels growing around the edge of the lake can'tfilter all the water in the middle of the lake.

"So, while there's still a lot of uncertainty about the magnitude of impacts in Lake Winnipeg, I suspect they're going to be smaller than we've seen in some other ecosystems," Higgns said.

It also means they may take care of some algal blooms in the lake but they're not exactly going to make it crystal clear there's too much water for that.

"Andthe growth rates of the algae are much higher than zebra mussels' ability to consume them. That's what the evidence suggests so far," Higgins said.

1 mussel, 1 million eggs

But through the narrows and into the northern basin of the lakethere's a lot ofhard, rocky lake bottom where zebra mussels can colonize, he said.

Once they can do that, they do it fast.

One mussel can produce up to one million eggs during a single spawning season, according to the Lake Winnipeg Foundation. And they are dense,withmore than 10,000 mussels per square meter in some places.

They also grow on the shells of native mussels, cloggingtheir intake filters and choking them out.

"There is a rule of thumb that basically says that, within 10 years of a zebra mussel invasion, you lose about 90 per cent of your native mussel population," Higgins said.

Now back to that filter-feeding that they do.

If they can spread out to the middle of the northern basin and blanket that rocky bottom, they could remove a lot of the sustenancefrom the food chain.

"It's possible thatas the water moves from the southern basin through the narrows and into the northern basin, the zebra mussels may be able to strip out the algae and the nutrients they contain," Higgins said.

"This is all speculative and we don't have any data yet, but it's something we're watching to make sure we catch this if it starts to happen."

Recent data from the province showszebra mussel larvae calledveligers are moving north and have already been found near MathesonIsland, at the south end of Lake Winnipeg's north basin, and as far north as George Island, more than 300 kilometres north of Winnipeg.

Hydro monitoring for mussels

Manitoba Hydro is in the midst of a plan toinstall a treatment system at its Grand Rapids Generating Station, as well as at the JenpegGenerating Station on the upper arm of the Nelson River.

"As the invasive zebra mussels spread, they pose a threat to pipes, pumpsand other equipment at Manitoba Hydro's generating stations," said spokesman Bruce Owen.

"[They] can attach to the inside surfaces of a generating station's intake pipes, plugging them up. These pipes supply water to cool turbines to prevent overheating and for emergency fire suppression."

Theplan is to use chlorine in thewater system used to cool the generators, while thefire protection system will be protected by using a potassium chloride treatment.

"However, I caution that this is simply a plan. Any potential treatment for zebra mussels is subject to federal and provincial regulatory approval," Owen said.

If approved, generating stations further downstream will be outfitted a little later,Owen said.

The first detection of zebra mussels onHydro infrastructure was at the Selkirk generating station in October 2015. The mussels had attached themselves to a water intake screen.

"The same year saw a single tiny zebra mussel larva [also known as aveliger]detected in Cedar Lake, upstream of the Grand Rapids generating station. Ongoing testing to date has found no adult zebra mussels in Cedar Lake," Owen said.

For the first time, this year Hydro is conducting aveligersampling program, he added, noting the only sampling until now has been for adult mussels.

Hydro employees willsample the following water bodies twice during 2018:

• Cedar Lake.
• PlaygreenLake.
• Nelson River upstream of the Kelsey and Kettle Generating Stations.
• AssiniboineRiver near Brandon generating station.
• Winnipeg River upstream and downstream of thePointeduBoisandMcArthurFalls generating stations.

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Frequently asked questions on mussels

• What are they and how did they get here?

Zebra mussels are an aquatic invasive species, which means they are not native to this region and can multiplyrapidly.

They are native to the Black and Caspian sea region of eastern Europe and are believed to have been carriedto Canada's Great Lakes by big ships.

They were first discovered in Lake Erie in 1986 and within a few years, they had spread to the rest of the Great Lakes.

After a decade, they were in all the Great Lakes as well assmaller inland lakes and rivers, and had spread as far south as the Gulf of Mexico.They now occupy over 800 lakes, mostly in eastern North America, according to Higgins.

• How did theyarrivein Manitoba?

They were first found in Manitobain Lake Winnipegin October 2013.

Evidence suggests that they came in via the Red River, either in the form of aveligeror as adults floating down the river, attached to debris or plant material, Higgins said.

It is also possible that they arrived overland attached to a boat or other equipment being transported from an invaded habitat. The closest invaded habitats are in North Dakota and Minnesota.

• Are there health concerns?

There are none immediately known, other than cuts from the sharp-edged shells.

Around rocky shorelines, caution needs to be taken so that people, especiallychildren, andpets aren't cut by the sharp shells. That means wearing proper footwear in the water.

In the Laurentian Great Lakes, it has been reported thatmussels helped developshoreline algal blooms from their waste productsfeces and urine. As those blooms washed up on the beaches, they became a cesspool for bacteria, Higgins said.

There are scientific papers about the beaches on Lake Michigan that suggestdecaying material was associated with a number of potentially pathogenic bacteriaE.coliand others that could pose a concern to human health.

So whenever officials saw these shoreline algal blooms washing in and staring to decay, they would essentially have to close the beach.

• What kills them?

That's what everyone wants to find out.

The province tried suffocating them with liquid potash in May 2014, and temporarily closed four harbours where zebra mussels had been found.

That killed some in Winnipeg Beach, Gimli, Arnes and Balsam Bay, but those areas have since been re-invaded. For big bodies of water, the potash gets too diluted.

• Manitoba hopes potash will kill zebra mussels in Lake Winnipeg harbours

Icebuildup on the lakes will crush the mussels, forcing the dead shells to wash up in spring. Some mussels, however, survive in crevices in rocks, then repopulate quickly in the spring when the ice is gone, Higgins said.

"So ice in itself won't kill off the population, unfortunately. They just keep rebounding every year."

• What can the public do?

The most important action that individuals can take is to ensure that they thoroughly clean items (like boats, boat trailers and buoys) removed from Lake Winnipeg before placing them in another water body, Higgins said.

As well, boat hulls, motors, water intakes and other "in-lake" infrastructure will likely require increased maintenance.