People and Places

THIS CITY: Zebra Mussels Wreak Havoc With Ottawa River Ecosystem

This article was originally published in the May 2015 print edition of Ottawa Magazine

Illustration by Michael George Haddad
Illustration by Michael George Haddad

By Matt Harrison

Stemming the flow of raw sewage flooding into the river after heavy rainfalls is one of the major problems being addressed by the Ottawa River Action Plan (ORAP). Indeed, earlier phases of the plan have already significantly reduced pollution entering the river. The final phase of the ORAP — building large storage tanks to contain overflow — is supposed to kick into gear this summer, but it requires provincial and federal funding, and so far, none has been promised. [Update: $65 million in federal funding was announced in April.]

But rethinking the Ottawa River isn’t such a bad idea. In fact, it may lead to a more holistic approach — one that addresses not only overflow but other factors affecting the health of the river.

The zebra mussel — and the herculean task of rescuing native mussel populations from its death grip — provides a perfect example.

“When the zebra mussel was first introduced into the Great Lakes ecosystem, it spread throughout like wildfire,” says André Martel, a zoologist with the Canadian Museum of Nature. Martel explains that since the arrival of the zebra mussel in the Great Lakes in the mid-to-late 1980s, native mussels such as the hickorynut mussel have been placed on the endangered list.

So named because of the black-and-white zigzag pattern on its shell, the zebra mussel hitched a ride in the ballast water of ships leaving their ports in Russia, boats that made their way to the St. Lawrence River and discharged that water — along with the zebra mussel stowaways — into the Great Lakes ecosystem. Martel suspects that zebra mussels found their way to Ottawa by clinging to the undersides of boats travelling from Lake Erie, up the Rideau Canal, and into the Rideau River.

Perhaps no one understands just how dire the situation is better than Martel, a 55-year-old marine zoologist and diver who regularly checks in on the mussel population in the Ottawa River.

André Martel looks at mussels collected from the shallow waters of the Ottawa River. Image: Jacqueline Madill © Canadian Museum of Nature


Martel dives in August, September, and October, when the Ottawa River is fairly clear and the current is low. Among the sunken trees and other objects, natural and man-made, Martel scratches around at the bottom of the river, searching for signs of native mussel life. It is a frustrating search, because the vast majority of the hickorynut population has been wiped out. It can take up to 20 minutes of underwater diving to find a single living native mussel.

For most of us, mussels are something that comes to mind only when we’re ordering in a seafood restaurant. Bivalve cravings aside, the hickorynut serves a far more vital function. Like a canary in a coalmine, the hickorynut (and 15 other species of freshwater mussels in the Ottawa River basin) reveals vital clues about the health of a river.

“On the Rideau River, we’ve gone from one of the richest rivers — in terms of its native mussel species in eastern Canada — to hardly anything left. The main reason has been due to the zebra mussel’s invasion,” says Martel.

A photo of something very few people get a chance to see: a Hickorynut in action in its natural setting. The mussel is filtering the water. This photo was taken in the middle of the Ottawa River at a depth of 4 m. Image: André Martel © Canadian Museum of Nature

Like many invasive species, the zebra mussel has no natural enemies in Canada, which means there is little to slow its spread. Nor has it evolved along with the native species. Zebra mussels are picky eaters — they consume only the good algae while leaving the bad. This can amplify a pre-existing problem of toxic algae that might exist in an area as a result of human activity, thereby reducing the oxygen in the river and suffocating fish. And the hunger zebra mussels have for the good plankton can deprive small fish of an important food source.

Meanwhile, the native mussels can’t do much in response, because zebra mussels are really good at attaching themselves to everything — including the shells of native mussels. All that extra weight impedes the native mussels’ ability to open and close their shell. It also prevents them from using their “feet” — muscular appendages that they contract to burrow in the sand. In what Martel calls the “earthworm effect”, native mussels use their foot to dig into the river bottom, carving oxygenating canals. But with a zebra mussel — or two or three — on their back, they can’t move so well, which means the native mussels can’t do their job of oxygenating the soil.

The burrowing also allows mussels to attract fish with their “eye.” Yes, in addition to feet, some female native mussels have an eye — it acts like a angler’s lure — that attracts large fish. Sturgeon, in particular, get tricked into thinking the eye belongs to a small fish and approach the mussel. When the big fish swims by, the mussel releases its embryos onto the gills and fins of the fish; those embryos hang on until they’re ready to “hatch” — thus spreading throughout the river.

But with zebra mussels preventing burrowing, those critical feet and eyes aren’t given the chance to do their respective jobs and reproduction isn’t possible.

There is some good news. Last June, Canadian conservation authorities announced the successful use of liquid fertilizer — potash — to kill invasive mussels on a test site in Manitoba.

Moreover, an important discovery last summer gave researchers something to cheer about. Martel and others found what is potentially the largest population of the rare hickorynut mussel in Canada near the town of Waltham, Quebec, in the Ottawa River. (For more on this discovery, check out this entry on the Museum of Nature’s blog.) This means that there are still pockets of the river where the hickorynut is doing its job — and thriving. And it gives experts like Martel a clue to how to rehabilitate the river and revive native mussel populations.

But all the blame for the state of the Ottawa River can’t be placed on mussels. After all, what species introduced zebra mussels into the rivers in the first place? (Hint: it rhymes with schmumans).

As Martel points out, we are also responsible for creating other stresses, such as dams, on native mussel species. “The Ottawa River is no exception. We’ve got dozens of dams on the river — it’s one of the more heavily impounded rivers in Canada,” says Martel.

Dams block the migration of fish up and down the river and prevent gene exchange among species, which reduces genetic biodiversity. They also prevent some species from spawning and alter the shape of rivers, often turning them into lakes, which quashes any species that rely on shallower depths and moving water, explains Martel. The sturgeon, a fish that plays a vital role in the reproduction of mussels, thrives in rivers — not lakes.

Last fall, when councillors at city hall were approving Windmill’s plan to develop at Chaudière Falls — and not return the falls to their former natural state, sans dam — it is doubtful that the well-being of the sturgeon was on the agenda. But if Chaudière is to be one of the most sustainable communities on the planet, the ongoing invasion by the zebra mussel, the plight of the hickorynut mussel, and the effects of the various dams, not to mention the dumping of raw sewage, should be part of the conversation.