
by Madelyn Anderson – Our last post introduced a collaborative project here at Haler Lab that is focusing on an invasive species called the zebra mussel. Led by Tyler Butts, the project is taking place both out on the waters of Lake Mendota and in the lab near its shores as researchers work to understand both how conditions in the lake affect the notorious species and how the zebra mussel, initially discovered in Lake Mendota in 2015*, is impacting the lake.
The study combines a deep-dive into decades’ worth of data, field-based observations being made out in Lake Mendota’s murky waters and experiments on zebra mussels being raised in the Water Science & Engineering Laboratory (WSEL) next door to Hasler Lab.
“The work we’re doing this summer is going to help us better understand how zebra mussels are interacting with phytoplankton and microbes in the lake,” Butts says.

I recently boarded a boat with members of Tyler’s team as they set out to sample five nearshore sites along the southern shore of Lake Mendota where zebra mussels are known to be present and two other sites where researchers have not currently documented zebra mussels.
When we anchored at the first site, it was undergraduate Sophie Corsaro’s turn to take water samples from the lake surface. Wind whipped through our hair as Corsaro lay on the floor of the boat, leaning out to scoop up green-tinted water with one arm. A potentially risky task, she completed it with a smile.
While Sophie worked, another team member used an instrument called a Van Dorn sampler to collect water from just above the bottom of the lake. Meanwhile, the rest of the crew took depth and clarity measurements.
“How can you complain about your job if you’re out on the lake?” laughed Corsaro. “Yeah,” undergraduate Joey Munoz agreed, “a big reason I’m in this field is because I feel so calm in and near water.”
The two described themselves as “blips in a sea of long-term data collection” as we headed to the next site and settled back into our seats on the CFL’s research pontoon, chatting about the project. I learn these samples are being taken at an interesting moment in the zebra mussels’ short history in Lake Mendota. .
“This summer, zebra mussels are in some kind of population decline,” Butts explains. “Species invasions often go through ‘boom and bust,’ periods which is why I think we’re heading into a ‘bust.’ There’s no telling whether they’ll boom again or stay at low densities for a while.”
Butts says that his project will “provide lake and experimental context to the impact of zebra mussels on planktonic communities,” and help answer the question “How does the invasion affect lower food web structure and diversity?”
The lake’s lower food web is dominated by tiny, free-floating plants called phytoplankton and algae. One way zebra mussels affect the aquatic ecosystem is by being picky eaters. According to Munoz, they prefer to eat non-toxic kinds of algae, spitting out the pesky bluegreens, or cyanobacteria, by coating it in a mucus layer and excreting it as a pseudo feces.
These feeding patterns can help the cyanobacteria responsible for toxic algae blooms out-complete other types of phytoplankton.

What’s unclear is how the process works in eutrophic – or nutrient rich – lakes like Mendota.
Out on the lake, the crew is pulling what looks like a PVC pipe full of water onboard the boat. The tool, called a Van Dorn sampler, allows researchers to collect water samples at specific depths.
“We collect Van Dorn pulls and bring large amounts of water back to run through chlorophyll and microbial filters,” explains research technician Joe Noeske. “This gives us a more in depth idea of how much photosynthesis is taking place in the lake, who is doing it, and where.”
Photosynthesis measurements offer a key indicator of plant life in the lake. Knowing more about the abundance of these tiny plants in the lake and if that abundance differs in areas of the lake with high zebra mussel populations or low mussel populations is crucial to the team’s work.
“We need to assess the interactions between the plankton community and nutrient dynamics in the zebra mussel’s local environment, and then conduct our own experiments to link our historical data and reveal zebra mussel feeding preferences in a eutrophic lake” says Butts.
It’s a tall order, especially as climate-driven variables like warmer waters and heavier rains spurs even more algae blooms in eutrophic lakes.
“The impacts invasive species and climate change have on each other and on a lake can be really hard to track and predict,” said Butts. “Their relationships can be synergistic, antagonistic, or additive. It’s important to be looking at invader impacts here in Mendota so that we can try and better understand them when they happen in other places.”
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EDITOR’S NOTE: In 2001, Wisconsin Department of Natural Resources fisheries biologist, Kurt Welke (now retired) found a single zebra mussel attached to a rock on a dive in Lake Mendota. No one is sure why that finding wasn’t followed by a bigger invasion but, in 2015, the discovery of a single mussel soon yielded sighting of thousands. Thanks to Madison’s Rick Krueger for the story!