The zebra mussel is a small aquatic animal with two shells like a clam, named for its striped shell. This tiny creature may look harmless, but it can cause big problems. The zebra mussel is an invasive species, a species that’s brought from its native area to a new place where it thrives and causes changes in the local habitats and communities.
Zebra mussels once lived only in freshwater lakes and rivers of Europe and Asia. But in the 1980s, they appeared in the Great Lakes between the United States and Canada. Scientists think the tiny animals were carried across the ocean inside of cargo ships. Within a few years, the mussels were found along waterways from Wisconsin to Arkansas.
How do these mussels spread so quickly? A single female can lay up to one million eggs each year. Then the young mussels float easily along water currents. When they are older, they attach themselves to hard surfaces like rocks on the riverbeds and the bottom of boats. They form dense colonies, with as many as 10,000 mussels in a single square foot. Each mussel clings with a mass of thread‐like strands, making these colonies nearly impossible to remove.
Zebra mussels pump water through their gills to filter out particles of food (primarily phytoplankton). An Unwelcome Newcomer Zebra mussels can cling to any hard surface — including native mussels and other shelled animals. These animals die because they can’t feed. Zebra mussels can upset food webs in other ways, too. These filter feeders pump water through their gills and strain out microscopic organisms called plankton. Zebra mussels can quickly clear out huge bodies of water, removing food for the native invertebrates and small fish. Zebra mussels can also affect humans—and cause millions of dollars in damage. The mussels clog water pipes to businesses and power plants. They damage boats, docks, buoys, and other structures. And their shells wash up in huge numbers on beaches.