We don't have to panic over zebra mussels

In Minnesota, these invaders are late to the lakes, and treatments are promising.

Five new zebra mussel lakes discovered in the metro region in the last two months prompted the Star Tribune (“Mussels’ march exasperates lake advocates,” Oct. 1) to report that some feel the state is “losing the battle” against this invader. But a look at the facts shows no scientific support for a zebra mussel epidemic out of control in Minnesota.

Zebra mussels arrived in Duluth Harbor in 1989, and in 1992 they reached the Mississippi River in Minnesota. So they’ve been here about as long as they’ve been in other states in the region. All other states with zebra mussels in more than 10 lakes (New York, Ohio, Michigan, Indiana, Illinois and Wisconsin) have experienced a common invasion “trajectory.”

After arriving in ballast water of transoceanic ships, zebra mussels spread rapidly in five years, filling the Great Lakes, then up and down the Mississippi and the large rivers connected to it. Next was a much slower process of inland invasion, occurring in three phases in each of these states. First was a lag phase with few or no new lakes, followed by a phase with a rise in spread rate, followed by a “plateau” phase.

What sets Minnesota apart is that the inland lake spread phase started recently, not 10 years ago as it did everywhere else in the region. Why so much slower in our state? It may have to do with geography. These other states have large source populations along expansive Great Lake shoreline, connected by high boater traffic to inland lakes. Lake Superior source populations are fewer and more localized, and have fewer paths of connection inland in Minnesota.

It appears likely that in Minnesota, zebra mussels took a slower route to inland lakes via boat traffic out of the Mississippi. But now large inland lakes (like Minnetonka and Mille Lacs) are infested, and these may serve as invasion sources for other lakes — which may help account for the current increase in spread.

It is also reasonable to suggest that Minnesota’s program of inspection and decontamination of recreational boats, along with raising awareness through Stop Aquatic Hitchhikers and other campaigns, has played a role in slowing the spread. It is nearly impossible for us to know the exact effectiveness of this program, as there is no controlled experiment we can look to. However, we do know that zebra mussels in Michigan spread to lakes with little or no prevention in place and that the spread there was among the most rapid. In earlier years of the invasion, states like Michigan were much less aware of the threat and what to do than we are today.

Treatments of newly infested lakes, such as were attempted over the last several weeks in Christmas Lake, are becoming more realistic options with increased availability of local resources. These approaches need to be tested and perfected, but they show real promise. New control measures will also be possible with dedicated long-term research programs. And with a better understanding of the pathways of spread (the focus of my research), prevention efforts may become more wisely targeted.

Not being a native, I can only hear (without full understanding) the frustration some Minnesotans voice with invasive species prevention and with the Department of Natural Resources. Wherever you fall along the range of sentiments, deciding to give up is the wrong decision. The claim that “it is only a matter of time until zebra mussels invade every Minnesota lake” is simply untrue.

We are now sitting at a time that is early — a time when we can make a difference — and with resources on the rise regionally, the challenge is on to be bold and creative with new measures to prevent and control the spread of zebra mussels.

Michael McCartney is a researcher at the Minnesota Aquatic Invasive Species Research Center (MAISRC) working to find solutions to zebra and quagga mussel problems in Minnesota. Funding for the MAISRC is provided by the Environment and Natural Resources Trust Fund and the Clean Water Fund.