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| 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.
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| Zebra
mussel, Dreissena polymorpha. |
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.
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The zebra mussels' invasion of the Rideau River was particularly concentrated, even spectacular, downstream from Kars to Ottawa. |
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All sections of the River saw an increase
in the abundance of zebra mussels. |
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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! |
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Researchers did not find any
native freshwater mussels alive in several sections in Ottawa, including
Sandy Hill and Mooneys Bay.
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This
graffiti is carved into a layer of zebra mussels on a
lock wall. |
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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. |
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| Zebra mussels on a boat hull. |
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.
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