Limnology in Action: Numb Feet and a Bucket Full of Rusties

The weather keeps alternating between chilly and warm as Lindsey Sargent, a graduate student from the University of Notre Dame, steers our small boat out into Star Lake in northern Wisconsin’s Vilas County. We’re on the hunt for the invasive rusty crayfish.

Today, Lindsey is out collecting crayfish to bring back to Trout Lake Station, where they will spend their summer as research subjects in big outdoor tanks. Lindsey pulls up to an overgrown bank and her team springs to action.

Aisha Liebenow and Rusty
Me and my first rusty. Photo: A. Hinterthuer

After watching Lindsey and her two assistants, Maggie Corcoran and Zach Welty, work away, crouching in the shallows in their wetsuits and catching crayfish by the dozens with their nets, I decide it’s time to give it a try.
Jumping barefoot into the frigid spring water in 60 degree weather is an initial shock, but once my feet go numb with cold, it’s not too bad! Snagging rusties proves more difficult than it looks, so I’m not much help, but getting over my fear of picking one up by hand is good enough for me.
Maggie Concoran makes sure each rusty is the "just right" size for Lindsey's experiment. Photo: A. Liebenow
Maggie Concoran makes sure each rusty is the “just right” size for Lindsey’s experiment. Photo: A. Liebenow

In contrast from previous work done on this widespread Northwoods invasive species, Lindsey is focused on a little parasite called a trematode. These particular trematodes are parasitic flatworms that spend part of their life cycle growing in the digestive tract of crayfish. Lindsey is interested in the behavior of rusties that are infected with these parasites and the resulting interactions with their community.
Lindsey hopes that, by getting these crayfish back to the lab, she can design some experiments exploring how infected rusties behave versus what’s known as “normal” behavior for their uninfected friends.
Rusties can have major impacts on lakes, feeding on and dramatically decreasing aquatic vegetation long lake beds, which can also drastically lower aquatic insect populations, causing a consequent decline in fish populations.
Rusty Underwater
This rusty crayfish was found dancing under our feet in Star Lake. Can you spot his tiny friend hiding by the rock? Photo: Lindsey Sargent

But this parasite may change the story of rusty impacts on lake ecosystems. Scientists known that trematodes can have effects on other species, include the ability to change the behavior of their hosts. For example, infected arthropods (or tiny aquatic crustaceans) will, in Lindsey’s words, “act crazy,” and swim up to the surface of the water where they are more likely to be seen and eaten by birds. In a way, this ‘suicidal’ response reminds me of a potential scene from the movie The Happening. For the trematode parasite, though, it’s a great way to move from one host to another.
These rusty crayfish await the completion of their new outdoor digs at Trout Lake Station. Photo: A. Hinterthuer
These rusty crayfish await the completion of their new outdoor digs at Trout Lake Station. Photo: A. Hinterthuer

In infected rusty crayfish, the extent of altered behavior is still to be determined but two qualities that have been consistently observed are increased aggression and decreased food consumption. With a slimmed down appetite and an inclination to stir up trouble, rusties may eat less and get eaten more. If that’s the case, vegetation and insects could bounce back, feeding a rebounding fish population as well.
Of course we won’t be any closer to answers to these questions until Lindsey can get her catch back to the lab and get her experimental tanks set up.
After a half hour lifting rocks and chasing the crayfish that darted out, my feet had had enough. I swung my legs back into the boat and let Lindsey’s crew take it from there. “So is this what you expected [for your summer job]?” I asked fellow undergraduate intern, Maggie Corcoran. She exclaimed (completely free of sarcasm of course), “it’s everything and more.”
Only hundreds more to go. These lucky rusties will soon move into lake-side digs, as research subjects at Trout Lake Station. Photo: A. Hinterthuer
And in a way, it really is. Who can say they spent an entire summer where ‘suiting up’ meant putting on a slick black wet-suit and snorkeling goggles to catch a colorful and feisty invasive species? Not many I’m sure.
Either way, it was a fun (and cold) filled day in the Northwoods, and I can’t wait to get back out there. Although maybe I’ll save the wading for when it’s a little warmer…

These are the first-hand ‘Notes from the Northwoods’, as UW – Madison undergraduate student, Aisha Liebenow, dives into the world of science, ecology, and aquatic systems. Follow her throughout the summer in her Northwoods emersion at the UW Center for Limnology – Trout Lake Station in BoulderJunction, WI.