Tiny Invertebrates and The Great Aquatic Migration

by Christina Weatherford, 2022 Trout Lake summer scicomm intern

Painting by Christina of a nightly zooplankton migration and a winner of the UW-Madison’s annual
Cool Science Image Contest

When looking at the lakes in northern Wisconsin, you might be struck by how scenic they are, or daydream about how many trophy fish they contain. For the scientists at TLS, however, this love of lakes extends to an appreciation of things that are often overlooked. This summer, a crew of TLS scientists and students worked to unravel the intricacies of a nightly mass migration that features miniscule creatures with massive importance.

Their focus is on tiny, free-floating critters called zooplankton. During the day, zooplankton stay near the bottom of lakes to avoid being seen by hungry predators. But, at night, they rise to the surface to eat algae. While that might not sound impressive, keep in mind that these tiny animals are so small that just a 10 meter-long trip up in the water column is 50,000 times their body length. That’s the equivalent of a five-foot-tall person going 50 miles to get dinner and, before daylight, going 50 miles back to where they started!

Zooplankton may be tiny, but they are crucial to the structure of lake ecosystems by grazing on algae and being the main source of food for most larval fish, many adult fish species, and other larger zooplankton predators. They also are surprisingly cool in their own tiny ways.

Bennett McAfee, who helped create modeling software for migration patterns as a student at Lawrence Univ., developed an appreciation for these little creatures during his summer on station. “The shear complexity of such simple-looking creatures is astounding. These little animals that you can only barely see with the naked eye and that most people don’t ever think about are capable of some fascinating behaviors and really complex interactions with other species,” says McAfee. “Zooplankton are a marvel of evolution and are incredibly important to the aquatic ecosystem, which makes them incredibly interesting.”

Eleanor Meng, another student at Lawrence Univ, came to TLS this summer to assist with the project. Although the study will undoubtedly help further her career, it also built excitement about a different outcome.

“On a personal level, I’m interested in increasing public awareness of [zooplankton] and other invertebrates using visual references and images,” Meng said. “They’re cute creatures and I’d love to share this side of aquatics!”

So, the next time you’re at a Wisconsin lake, take a second look at the water before you. While you might not be able to see them, now you know that, somewhere down below, thousands upon thousands of tiny, little zooplankton are awaiting nightfall so that they can begin the epic daily migration that plays such a critical role in the health of the lake.