Invasive species change Minnesota lakes

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MPR Photo/Dan Gunderson

Aquatic invasive species are drawing a lot of attention in Minnesota. Invasive plants like Eurasian milfoil have been common in Minnesota lakes for years. But new invasive species like zebra mussels and Asian carp are causing a higher level of anxiety about their effects on Minnesota's beloved lakes.

Many invasive species arrived via Great Lakes shipping. The U.S. Geological Survey has identified more than 136 exotic species that have established populations in the Great Lakes.

That's how the zebra mussel arrived. This animation created by the U.S. Geological Survey shows how the invasive invertebrate spread.

Geological Survey officials say once an exotic species is established, control efforts are very expensive and rarely successful. Just one invasive, the zebra mussel, is expected to cause billions of dollars in economic effects over the next decade.

Invasive species often have a variety of impacts on the ecosystem.

The zebra mussel, for example, is a filter feeder. That means each mussel filters up to a gallon of water a day, eating the plankton at the bottom of the food chain.

That means less food for some species of fish.

It also means increased water clarity in lakes. In Lake Erie for example, water clarity increased from a few inches to 30 feet as a result of zebra mussel filtering.

Light then penetrates deeper, and aquatic plants grow much larger. That's good for some species of fish like the northern pike, or bass, but all that weed growth hampers boating or swimming in lakes, and can reduce the lakes ability to support fish populations over time.

I often hear people say zebra mussels have no natural predators in Minnesota. That's not the case — Geological Survey officials say there is evidence migrating waterfowl have changed their flight patterns to feed on zebra mussel colonies.

Fish like sturgeon, catfish, freshwater drum and sunfish all eat the tiny zebra mussels.

But the mussel is so prolific, its population generally grows rapidly, despite predators.

Scientists say preventing the spread of zebra mussels is the only effective control. There are chemicals that will kill zebra mussels, but they're mostly used in small areas such as around water intake pipes.They have not successfully been used to treat an entire lake.

The state Department Natural Resources has experimented with pesticides to control an early infestation of zebra mussels. But the verdict on that approach is not in.

Minnesota officials are focusing on prevention with expanded boat inspection and decontamination. The state is also requiring workers who move equipment like docks and boat lifts to be trained to recognize aquatic invasive species.

Zebra mussels are commonly thought to hitch a ride from lake to lake on boats, but can just as easily travel on the boots of someone who goes from lake to lake installing or repairing docks, or on the gear of scuba divers or swimmers.

Listen to my report on how Minnesota lake associations hope to spur action against invasive species on today's All Things Considered.

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