Species: D. polymorpha
Today, we’re going to talk about zebra mussels. We’re not going to talk about zebra muscles like I had originally written down on my blog schedule. Honestly, why would I talk about the muscles of a zebra? They’re not even aquatic!
I know that was a lame introduction. It just doesn’t have enough strength to land a clever opening—maybe it needs more mussels…
Okay, I’ll stop!
Zebra mussels, D. polymorha, are freshwater bivalves native to Eurasia. Bivalves are shelled creatures; specifically mollusks with two shells that close together, like clams and oysters. Zebra mussels are about an inch long and are shaped liked a stretched out “D”. They are named from the black, zigzag patterning on their shells.
Humans can be so creative with their naming schemes.
Zebra mussels have a relatively short life span, between 2‒5 years, reaching reproductive maturity at 2 years of age. Each female can produce up to a million eggs per year, spewing them into the surrounding water and using the currents to transport the eggs.
The reason I’m bring up D. polymorpha is because it is an invasive species in the United States and Canada. The mussels were first discovered in the early 1980s near the Great Lakes and are believed to have been transported by accident in the ballast water of a ship. Since then they have been found in the Great Lakes, the Mississippi and St. Croix rivers, and the Chesapeake Bay.
Why are the zebra mussels bad for these environments? Don’t they help filter the water in their surroundings, and isn’t that a good thing?
In their natural habitat their job as filter feeders is absolutely amazing; in other habitats, it can have devastating effects. In fact, zebra mussels are so efficient as filter feeders that they can clean a body of water of particulates in record time, faster than the native filter feeders. But this is not a good thing.
The environments that the mussels invade have a special balance that is maintained by the native populations of animals. If you change one aspect of that balance, then it creates a domino effect.
Let’s say that we have an imaginary river, the River Sága, which is home to large, healthy beds of freshwater bivalves called blue purses (not a real bivalve). In this river there are also a few species of fish that go there to spawn and where the juvenile fish live until they’re big enough to move on. One day, an old fisherman dumps water into the River Sága from his boat and unknowingly releases several thousand eggs of the zebra mussel. A couple of years later, the river is no longer the same. The once-healthy beds of blue purses are now completely covered in smaller bivalves, smothering the native species. The water of the river is the clearest it’s ever been, but downstream there are enormous patches of algae, and there are no fish to be seen. What was once a nice fishing spot for man and animal alike is now barren, save for the zebra mussels and the algae.
Zebra mussels, like any invasive species, are horrible for the environments that they infiltrate because they have no natural predators, and they often outcompete the native species. Because zebra mussels are so good at filtering the water, it makes it easier for predators to find their prey in the water, whether it’s a larger fish or a bird hunting the juveniles that have spawned there. And because zebra mussels reproduce so much, they can easily smother their competitors, becoming the dominate species of the environment and changing it for the worse.
Zebra mussels also have an impact on human property. They have been known to block the drainage pipes of factories. They can incapacitate boats by clogging pipes and engines, or even by covering the sides of the boat and making it too heavy to float properly. It can take an absurd amount of money to remove them, and we have to do it often because they regularly come back and are so hard to eliminate.
I wanted to talk about zebra mussels because they have been noticed in the Chesapeake Bay, which is an important part of my life, and because it helps introduce the topic of invasive species. From what I understand, there is not much you can do once the zebra mussels appear, only that we must strive to prevent their spread elsewhere. But this also means that there is a potential opportunity for you, because maybe you can find a way to remove them from their nonnative habitats.
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