Posted by Angie Hong | Posted in Aquatic Biology | Posted on 02-12-2013
Tags: St. Croix River, zebra mussel
This is an alert from your emergency broadcasting system. Aliens are slowly but steadily infiltrating our favorite places in Minnesota. Just this September, the Minneapolis Park and Recreation Board confirmed that an aquatic invasive species known as the zebra mussel has been found in Lake Hiawatha in Minneapolis. According to the Minnesota Department of Natural Resources (MN DNR), these alien invaders have already infested more than 130 lakes and a dozen rivers in our state, including Lake Winnibigoshish, Lake Pepin, Mille Lacs, Prior Lake and Lake Minnetonka.
Federal and state officials in Washington County have been on the offensive since zebra mussels first showed up in the St. Croix River back in 1995. Said one local water educator, “We’ve got a message for those sneaky little bivalves: Not in our backyard zebras. Go back to the Caspian Sea.”
Intelligence reports indicate that zebra mussels originally hitchhiked from Russia to the United States in the ballast water of large ships. They were first discovered in Detroit’s Lake St. Clair in 1988 and since then, have spread throughout the Great Lakes and the Mississippi River Basin, causing economic and environmental damage along the way. By 1995, zebra mussels had made their way to the St. Croix River, and by 2000 the MN DNR declared the entire reach of the river from the Boomsite Recreational Area (river mile 25.4) to the confluence with the Mississippi River to be infested. In response to this foreign invasion, the National Park Service (NPS) set up a check point in the St. Croix River just north of Stillwater to prevent humans from unknowingly traveling upstream with tiny little aliens clinging to the bottoms of their boats. South of the checkpoint, however, zebra mussels continued to proliferate.
Female zebra mussels produce 100,000 to 500,000 eggs per year. During the brief three-week period that young larvae are mobile, they spread by floating in the current or hitching a ride with unwitting boaters. After that, zebra mussels anchor themselves to any hard surface within reach, including boat docks, pipes and sometimes even the shells of helpless native mussels. Downriver of Stillwater, NPS divers began finding thousands of zebra mussels per square meter coating the river bottom.
Then in 2012, the aliens mysteriously disappeared from the St. Croix River without a trace. Once again this spring, they were nowhere to be found. Could it be that the mother ship had finally called them home?
It appears that the river herself, perhaps frustrated with our ineffective attempts to keep zebra mussels at bay, decided to fight back. During June and July of 2011 and 2012, at the time of year when the aliens were reproducing, the St. Croix River sent record amounts of water downstream. In addition, common carp, an invasive species themselves, started eating the zebra mussels. It is worth noting, as well, that non-native species don’t always succeed in taking over every lake and river they infest; sometimes native populations are strong enough to resist the invaders and hold their ground.
Despite the temporary reprieve for the St. Croix River, zebra mussels and other aliens continue their attempts to regain control within the St. Croix and spread to more lakes and waterways across the state. We can’t let that happen. If we don’t introduce new zebra mussels to the St. Croix River, their populations might not rebound to as high of levels as before and there will be more time for native mussels regain lost ground as well. Our efforts will help to keep invasives out of new lakes and rivers as well.
Help mount the offensive against alien invaders. Anytime you move boats or personal watercrafts from one water body to another, remove visible zebra mussels and aquatic plants and drain out all of the water. If you are leaving a zebra mussel infested lake or river, spray down your boat and trailer with high pressure water, rinse with very hot water (120°F for at least 2 minutes or 140°F for at least 10 seconds), and let the boat and trailer dry for at least five days. If you live on or have a cabin on a lake, you can help the MN DNR to track the spread of zebra mussels by participating in the Zebra Mussel Monitoring Program.
The zebra’s on the run in Minnesota. Let’s keep it that way.