Rideau Canal - Musseling In
The origins of a virulent invasive species.
EPISODE NOTES
The ways in which zebra mussels take over the existing ecosystem can sometimes feel downright sadistic. Among the harms they can do to local species, they can actually grow on top of larger native mussels, sealing them shut and suffocating them.
TRANSCRIPT
From our first day out on the Rideau canal, I noticed a pattern. Every time I dunked a camera in the water, anywhere in the canal, I was seeing the same thing - zebra mussels.
They’re an aggressively invasive species who’ve been the bane of the Great Lakes for decades. But when they arrived in the Rideau Canal - they must have thought they had died and gone to heaven. Because here, they found three things that let them overwhelm these waterways.
Zebra mussels are first described in 1769 in the Ural, Volga and Dnieper rivers, where they’re integrated into the ecosystem, with natural checks on their growth and spread. And all was well, for about 219 years. Until 1988, when out of nowhere they show up in the Great Lakes.
Blame ship ballast: water taken on to make big cargo ships more stable as they cross the ocean. Those ships pick up water in the mussels’ native habitat, and dump it when they make port - say, in Toronto harbour. Even if they’re on the lookout for stowaways, zebra mussel larvae are microscopic. There’s no way to know that they’re releasing an invisible, invading army.
In an ecosystem that doesn’t know how to deal with them, the mussels spread fast. Within two years, they’ve reached the Rideau river and canal. The Great Lakes were already… Great… Lakes for the mussels, but this was paradise in three important ways.
First - no natural predators. Some fish and diving ducks will eat them but they don’t have any dedicated predators to keep their numbers in check.
Second - the flow of water. Zebra mussels eat by filtering, so they love moving bodies of water where that flow of nutrients is consistent and strong. Plus, they spread by releasing larvae into the water - up to a million per year per mussel. Moving water lets those larvae spread quickly. And here, they can actually move upstream by hanging onto boats.
Third - the geology of the canal. Zebra mussels build their shells out of calcium carbonate. They get their supply the same way they feed, by filtering dissolved calcium carbonate from the water. And the bedrock of the Rideau has a lot of limestone, which is mostly made up of, you guessed it, calcium carbonate. So they have a constant supply of shell-building material flowing past them.
These three factors have lead to an explosion in zebra mussels. Five years after they were first seen in the Rideau waterways, some estimates say their numbers have increased 100,000 times. Now, there can be up to 300,000 mussels in a single square meter.
So what do we do about them? The thing is, in the zebra mussel paradise of the Rideau, it’s almost impossible to get rid of them, which is why now people work on mitigation and prevention, to try to limit their spread.
But that’s not to say we haven’t tried… pretty much everything: Chemical oxidation, Mechanical Removal, Thermal Treatment, Foul Release Coating, UV Light, Low Frequency Magnetism and Pulse Acoustics. The sheer scope of mitigation methods tells you how difficult they are to deal with, and that deserves its own video down the road. For now, they’ve become an unfortunate fixture of the canal - wherever you happen to stick your camera in the water.