Posts Tagged ‘Zebra Mussels’


When this summer’s drought left the riverbed dry, it afforded the opportunity to look for freshwater mussels. Members of the Phylum Mollusca, mussels are related to snails, slugs, clams and oysters, and even octopuses. Mussels are sometimes called living filters. They play an important role in aquatic ecosystems by cleaning the water. They also provide food for assorted fish and wildlife such as raccoons.

There are 41 native species of mussels in Ontario. Of these, 28 species are in decline or threatened with extinction. Mussels are among the most endangered organisms in North America, threatened by many human activities from pollution to habitat destruction.

Perhaps the most severe threat to the native mussel population has been the introduction of the zebra mussel, an invasive species. Zebra mussels attach themselves to the shells of native mussels by the hundreds or even thousands, causing them to die from lack of oxygen or food. Native mussels have been nearly eliminated from much of the Great Lakes system and St. Lawrence river, as well as watersheds where zebra mussels have been introduced.


Eastern Floater (Pyganodon cataracta)

Freshwater mussels are the largest and longest-living freshwater invertebrates in North America. Their life spans can reach many decades. They occupy a wide variety of habitats, from small streams to lakes, but have their greatest diversity in large rivers, which supply a constant supply of oxygen and food and a variety of habitat types.

Mussels spend their lives buried in the substrate of their aquatic home. They feed by drawing water in through a siphon and passing it across gills to filter out small particles of algae and bacteria. The reproductive cycle of freshwater mussels is amazingly complex.

During spawning, males release sperm into the water and females living downstream take in the sperm through their siphons. Eggs are fertilized in a specialized portion of the female’s gills called marsupia. Embryos remain in the gills until they have reached a larval stage called glochidium.


Giant Floater (Pyganodon grandis)

When conditions are right, depending on temperature, photoperiod and time of year, the female mussel releases her glochidia into the water where they must quickly attach themselves to the gills or fins of an appropriate fish host. The glochidia then become encysted in the tissues of the host fish and get nourishment from its body fluids for a time ranging from a week to over 6 months.

They transform into juvenile mussels during this parasitic phase. Once metamorphosis is complete, the juvenile ruptures the cyst and falls to the river bottom, where it burrows into the mud and remains for the next few years. Most mussel species have only a few specific host species and the chances of a glochidiium surviving are low. Mussels produce millions of glochidia to improve the odds of some reaching adulthood.


Eastern Lampmussel (Lampsillis radiata)

I found evidence of 3 species in our local riverbed. Some of the Eastern Floater shells were quite large and sturdy, while the single Eastern Lampmussel I found was small and more fragile, a real beauty with striking green rays.

Mussels are an example of the astounding lives lived by so many creatures to which most of us are oblivious. Perhaps if Canadians had a greater awareness of the wonderful richness and diversity of life that surrounds us, and how little we know and understand it, they might be less apathetic regarding cuts to scientific research and the protection of waterways.


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After we enjoyed our lunch looking out over the bay, we rejoined the trail, which climbs up the cliff edging the bay. After following the bay shoreline for a short distance, the trail curves inland and circumvents a beaver pond.


We soon realized that we had been lulled into a false expectation by the first 4 kilometres of the trail, which are pretty easy hiking. After leaving the 4 KM marker behind however, the trail becomes much more challenging, with a lot of climbing and descending over rocky and rooted surfaces. We followed directions in a trail guide when setting out on the west arm of the loop first and this was terrible advice. It would be much better to do the difficult section first, while you’re fresh, and enjoy an easy walk back to the trailhead.


We were looking forward to the reward of a nice view from the lookout, but it was disappointing. Perhaps when the leaves drop from the trees the view is better, but we only got a distant glimpse of Charleston Lake.

Here’s RailGuy at the top of a rocky pass.


And climbing up through another rocky pass.


The vegetation included assorted ferns and woodland plants, and some interesting green clumps with long, narrow leaves. They were very attractive and I wondered what they are. Seabrooke posted an inquiry for me and they were identified as Plantain-leaved Sedge (Carex plantaginea), not what I think of as sedge at all. They are a native woodland broad-leaved sedge that flowers in spring.


At the 7 KM marker, the floating bridge could be spotted through the trees. The bridge crosses the mouth of Slim Bay. It’s fun to walk across as it rocks as you walk, though it has rods attaching it to large rocks to stabilize it.



The water is fairly shallow. It looks to be about a metre deep and there is a dense growth of water plants along the length of the bridge. However, right in the centre of the plants there was a ring of open water, tinted a milky yellowish shade.


Little fish were swimming within the circle, probably a Shiner (Notropis spp.)species.


I was puzzled and intrigued by this phenomenon. It gave the impression of some secret underwater vault, a mermaid’s haunt maybe.

The Zebra Mussels, on the other hand, were no mystery. They coated the struts holding the bridge in place and could be seen in the shallow water covering the sandy bottom of the bay. Zebra Mussels (Dreissena polymorpha) are a very unfortunate introduction to the Great Lakes ecosystem, probably imported in the ballast water of ocean-going vessels traversing the St. Lawrence Seaway. Their negative impacts include the decimation of native mussel populations and they have been connected to botulism outbreaks that have killed many loons.


After leaving the bridge behind, we were soon climbing again. The trail follows the cliff edge of Slim Bay and offers some nice views of the water below.


Finally, we arrived at the 9 KM Marker. Here is RailGuy, looking fresh as a daisy. After this marker, you soon rejoin the path to the trailhead and the final kilometre is an easy walk back to the parking lot.


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The Upper Canada Migratory Bird Sanctuary, east of Morrisburg, encompasses an area that was once the site of the town of Aultsville. The village, like nearly a dozen small communities along the St. Lawrence, was flooded during the development of the St. Lawrence Seaway and hydroelectric project. The towns have been dubbed the “Lost Villages“. In the fall, when water levels are low, you can follow the hiking trails at the bird sanctuary to the part of the river where Aultsville once stood and still see foundations from the old community. Standing on the little beach, above, you can just make out the remains of a roadway running off into the water.


Looking south, you can see a row of gulls resting on foundations submerged just below water level. We met an old-timer on the beach who told us that the water level was rising again. When he had visited a couple of weeks earlier, much more of the foundations and roads were visible. He attended high school in Aultsville more than 60 years ago and still returns regularly to visit the town.

It’s a pretty spot. Looking out over the river, you can see mountains on the horizon, the Adirondack Mountains in New York State.


As I was standing on the beach, I noticed that there were lots of little shells scattered about my feet. I picked up a half a dozen of them and brought them home to look at more closely. The shells are all worn and scuffed and their original shell patterns have disappeared, but some of them were likely striped. They’re foreign invaders: zebra mussels (Dreissena polymorpha).


Like the flooding of the “Lost Villages”, the introduction of Zebra Mussels to the great North American inland seas is a result of the Seaway development. But while the people of the Lost Villages were relocated and moved on with their lives, the Great Lakes ecosystem has been irrevocably damaged. Native to the Black and Caspian seas, the mussels were inadvertently introduced to North America via the ballast water of ocean-going ships traversing the St. Lawrence Seaway. They were first detected in the Great Lakes in 1988, in Lake St. Clair, located between Detroit, Michigan and Windsor, Ontario.


Crayfish encrusted with zebra mussels

Young zebra mussels are small and can be easily spread by water currents. Older zebra mussels attach themselves to hard surfaces using ‘strings’, byssal threads, which come out of their hinged side. Native mussels do not attach themselves to surfaces in this manner, but bury themselves in sand. Often, the hard surface zebra mussels attach themselves to on the silty bottom of rivers and lakes belongs to a native mussel. Thus encrusted, the native mussel cannot function and dies. Thus, zebra mussels are decimating the native mussel population.


Zebra mussels cause millions of dollars worth of damage every year. For example, it will cost the city of Buffalo four to five million dollars to remove zebra mussels that are clogging the city’s water intake pipe .

Zebra mussels do have some positive impacts. For example, many native fish species eat zebra mussels. However, they do not feed heavily enough on zebra mussels to keep the populations under control.

From an initial stronghold in Lake St. Clair, zebra mussels have been widely introduced to other waterways, often as hitchhikers on recreational craft. The map below shows their range in 2008, two decades after they were first identified in the Great Lakes region. Stars indicate where zebra mussels have been found on boats on trailers, but have not been confirmed in local waterways. Yet.


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