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Health of the Rideau River


Danger! Zebra Mussels Are Invading

Zebra mussels on a native mussel.
These zebra mussels are covering a native mussel, in Mooneys Bay.

The greatest threat to native freshwater mussels mussels in the Rideau River is from the invasion of the zebra mussel, Dreissena polymorpha.

Zebra mussels are small: as adults they measure approximately between 20 and 30 mm. During the larval stage they swim freely for a few weeks. In the juvenile stage they attach to a rock or other hard surface, and regrettably, native freshwater mussels are often used as support. Zebra mussels attach with strong, enzyme-coated threads that prevent the native mussel from feeding, breathing and moving normally.

Zebra mussel, Dreissena polymorpha.
Zebra mussel, Dreissena polymorpha.
The Invasion of the Rideau River
In 1990, zebra mussels were first found in the Rideau River at Mooneys Bay. Researchers with the Rideau River Biodiversity Project have been able to measure the rate of the zebra mussels' invasive progress, using information gathered both before and during the Project.

Bullets. The zebra mussels' invasion of the Rideau River was particularly concentrated, even spectacular, downstream from Kars to Ottawa.
Bullets. All sections of the River saw an increase in the abundance of zebra mussels.
Bullets. The mussel count between Smiths Falls and Burritts Rapids averaged 75 per square metre. Between Long Island and Ottawa the count ranged between 100,000 and 500,000 per square metre. The lock walls along this length were so thick with zebra mussels that the walls were not even visible and zebra mussels were growing on top of zebra mussels!
Bullets. Researchers did not find any native freshwater mussels alive in several sections in Ottawa, including Sandy Hill and Mooneys Bay.
"Zebra rules": Graffiti carved into a layer of zebra mussels. This graffiti is carved into a layer of zebra mussels on a lock wall.
Bullets. In the two years previous, the zebra mussel population has appeared to stabilize in Ottawa, but this does not mean that the zebra mussels will disappear. Rather, scientists believe that in this section the limit has been reached as to the number of zebra mussels the environment can support.

Zebra mussels on a boat hull.
Zebra mussels on a boat hull.
A Stowaway from Europe
Zebra mussels, an invasive exotic species were transported from Europe to North America in the ballast water of ships. First discovered North America in Lake St. Clair, Ontario in 1988, it is believed that zebra mussels were introduced into the lake in either 1985 or 1986.

The facility with which zebra mussels reproduce partially explains their invasive success. For example, a female is able to lay up to one million eggs during a single breeding season!

Zebra mussels disperse downstream on water currents during their free-swimming larval stage. Dispersal upstream and into inland rivers and lakes occurs with human activity: larvae are dumped from livewells and older ones attach themselves to boats.

In the almost complete absence of predators, zebra mussels invaded the Rideau River very quickly.


 Health of the River  

Watch this video!
Diver holding mussels.

A diver finds zebra mussels affixed to a native freshwater mussel.

(540 Kb, QuickTime)
A Project of the Canadian Museum of Nature
 Images: Canadian Museum of Nature, Ed Hendrycks, André Martel, Diane Pathy