Monday, February 8, 2021

Zebra Mussels May Not End (Lake) Life As We Know It

 Fall Newsletter Article by Jim Blodgett

In the Zoom educational session on Zebra Mussels sponsored by LLAA on Thursday, October 22, Nicole Kovar, MN DNR Invasive Species Specialist, Northwest Region, provided a terrific overview about the life and practices of Zebra Mussels and the potential effects of said life and practices on Long Lake. Then followed an extensive Q & A session, and I’m here to tell you that we need not retreat wailing into the woods or put our cabins up for sale before word of Zebra Mussels in Long Lake gets around.

It is true that Zebra Mussels propagate at insane rates, a single one annually producing hundreds of thousands young, or as they are called, veligers. It is this invisible horde of veligers adrift in the lake that makes it important to eliminate the transportation of water between lakes, whether in bait buckets or fish wells or any other such containers. If moving bait to another body of water, replace the original water with bottled water or some other untainted water.

At four weeks veligers are only one millimeter long. By then they have started attaching themselves to solid surfaces with tiny filaments called byssal threads. These threads form extremely strong bonds to whatever the veliger settles on – rocks, docks, anchors, boat lifts, boat bottoms and motors, rafts, trampolines, the underside of recreational lily pads, native clams, other Zebra Mussels, and even plants. It is the attachment to plants that makes it important to eliminate their transportation between lakes. The first Zebra Mussel found in Long Lake was attached to a pond weed at the South Access.

The maximum length of a Zebra Mussel at the end of its first year is 1/4” to 3/8”. Any longer than that have been around for more than a year. Their presence is not particularly noticeable at the end of their first year in a lake. Following their introduction into a lake comes a lag period during which their numbers grow incrementally. This lag period is followed by a time of exponential increase, and people suddenly notice that the Zebra Mussels “are everywhere.” The length of the lag period varies greatly among lakes. Factors determining this length include the water’s temperature and its chemical makeup. Zebra Mussels do not propagate below 54° F, so a lake’s depth and water sources help determine the length of the breeding season. The amount of calcium in a lake helps to determine how quickly or slowly Zebra Mussel shells grow. Long Lake, unfortunately, has a robust calcium content.

Such differences among lakes result in large differences in the time by which Zebra Mussels’ population growth becomes exponential. Leech Lake took six years before its Zebra Mussel population growth hit overdrive. On the other hand, Cass Lake required only one year. Exponential growth continues until it finally plateaus at the lake’s carrying capacity. Zebra Mussel numbers do not wane significantly since they have few natural predators in Minnesota, unlike in their native Euro-Asian water bodies where predators keep their numbers in check. The few natural predators in our part of the world, such as sheepshank fish and diving ducks, simply cannot control such large numbers.

Mature Zebra Mussels feed by filtering tiny life forms out of the water. One Mussel filters about a quart of water a day. This filtering has great effect: Lake Winnibigoshish doubled in clarity in one year. We usually see clarifying our lake’s water as desirable (and it is), but too much clarification in a short time through removal of tiny life forms can significantly upset a lake’s ecology, upending fish and plant life. The Zebra Mussel shells themselves differ from those of our native crustaceans. The shells of our snails, for example, pulverize when dead, but those of the Zebra Mussels break into shards that can cut peoples’ feet.

The presence of Zebra Mussels in Long Lake will make a difference in the lives of us who live on the lake. Total eradication is not a realistic goal. We will need to keep boats and their motors on lifts, out of the water, when not actually using them. We may need to rake our swimming areas and perhaps take to wearing water shoes. Zebra Mussels will not affect the use of docks and lifts.

Meanwhile, the Minnesota AIS Research Center at the University of Minnesota Twin Cities is conducting many research projects related to Zebra Mussel control. Some promising projects involve the use of copper compounds, and the recently completed decoding of the Zebra Mussel genome allows exploration of genetically based control, perhaps, for example, rendering Zebra Mussels infertile through gene splicing. Such cures, of course, will take years to develop, refine and implement, but in the meantime we can continue to enjoy the pleasures that our lake provides.

To view the video from Nicole Kovar’s presentation, go to:

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