Z is for Zebra Mussel

The invasive zebra mussel is named for the alternating brown and yellow stripes on its shell.

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The zebra mussel may not look menacing, but this tiny invader wreaks havoc on its adopted ecosystems.

Illustration Z is for Zebra Mussel with Mussels on a Crab

The small, freshwater mussel—named for the alternating brown and yellow stripes of its shell—is native to Eastern Europe and Western Russia. In the 1980s, it was discovered living far from home in the Great Lakes. The zebra mussel had managed to make its way across the globe, likely by hitching a ride in the ballast water of a visiting vessel.

Arriving in a body of water with plenty of nutrients and no natural predators, the hardy bivalve quickly became a troublesome invasive species. Specialized small, sticky fibers, called byssal threads, that extend from the zebra mussel's body allow it to attach to nearly any solid surface.

They stick to boats, buoys, docks, rafts, nets and ladders. Though barely the size of a thumbnail, in large quantities zebra mussels can clog intake pipes, mucking up municipal water supplies and power plant pumps.

They even colonize the shells of native mussels and crustaceans, often to the detriment of the host. Some endemic mussels have been found with more than 10,000 zebra mussels growing on their shells.

Close-up of a Zebra Mussel on Sand

Zebra mussels are prolific breeders, producing an estimated 5 million eggs in a lifetime, with approximately 100,000 surviving to adulthood. That makes them difficult to eradicate. Their free-swimming larvae, called veligers, can be unwittingly transferred between bodies of water via bait buckets and ballast bags. To compound the problem, adults can survive for days out of water, weather conditions permitting.

If the zebra mussel has one redeeming quality, it is the ability to filter large quantities of water, but even that has some unexpected consequences. The tiny filter feeders primarily eat algae and phytoplankton and can filter about 1 liter of water per day in the process.

The resulting clear water means sunlight penetrates to greater depths, which can accelerate the growth rate of aquatic vegetation, increase water temperature and alter its chemical composition. Additionally, the mussels' overconsumption of phytoplankton increases competition for resources, and the pollutants accumulated in their tissues can be passed up the food chain.

Oceans A to Z More in this Series

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