Are freshwater sponges a bellwether for healthy waters?
At the University of Minnesota Crookston, researchers put freshwater sponges—and their ecological roles—under the microscope.
If you’ve ever been to a clear, sky-blue Minnesota lake or stream, you may have seen, or even stepped on, one of the state’s most elusive residents: a freshwater sponge.
More than a thousand miles from the nearest ocean, these unobtrusive little animals have lived for millennia in our waters, both adjusting to and modifying their watery homes. At the University of Minnesota Crookston, faculty researchers like Timothy Dudley (chemistry), Venugopal Mukku (chemistry), and Karl Anderson (biology) and several student researchers have been unlocking the secrets of this ecological give-and-take since 2016.
Among the big questions this team continuously revisits: What species live in our water? What do they do? What can they tell us about our waters? Perhaps the biggest question is whether freshwater sponges can serve as bio-indicators of water quality.
The team’s work could help prevent health problems linked to poor water quality in Minnesota’s lakes and rivers. If sponges are scientifically demonstrated to thrive only in water that met certain standards of cleanliness, their presence could be a guide to which waters were safe for drinking, fishing, or watersports.
Donning waders and sometimes scuba gear, the team has collected sponges from streams and lakes across Minnesota. They were growing on all manner of solid surfaces, such as stones, cables, and even the wreck of a 1960s fiberglass runabout boat resting about 20 feet down in Pickerel Lake, Becker County.
Working alongside them, their students have enjoyed a first-class education in sponges, field work, and sophisticated biochemical techniques.
Students and recent graduates like Sierra Strenge '25, John LaCoursiere '24, and Paige Pitlick '20 took the campus’s hands-on learning approach to another level with freshwater sponge research. Pitlick initiated the study of sponge extracts, which provided the sponges’ chemical profiles and led to concepts about their intramolecular forces that are now taught in courses. Strenge and LaCoursiere were involved in sponge location, chemical analyses of water samples, and the biological processing of the collected sponges.
Simplest animals, complex roles
Like their household counterparts, the bodies of sponges are extremely porous, as evidenced by their membership in the phylum Porifera. Most freshwater species have “skeletons” of hard, needle-like elements called spicules. They build their spicules from silica, a mineral composed of silicon and oxygen. In one recent project, then-undergraduate Strenge studied whether the amount of silica in the water has any effect on sponge growth.
But while their bodies contain different types of cells, sponges are not organized into separate tissues as our bodies are. Instead, they have just one tissue and are thus recognized as the simplest multicellular animals. They feed on whatever they can filter from the water—bacteria, algae, tiny animals.
In collecting their samples, the researchers also record not only the location of the body of water, but factors such as its pH, temperature, dissolved oxygen, and conductivity—a measure of dissolved ions like salts, minerals, or pollutants, which affect the water’s ability to conduct electricity and can be an indicator of water quality.
Former student Michael Laurich searches a sponge sample for budlike reproductive structures called gemmules.
Photo by Steve Philbrook
Back in the lab, the team uses DNA sequencing to help understand the interactions between sponges and their habitats and their roles in the evolutionary cycle. They identify the species—and look for new ones—by techniques that include electron microscopy, which can reveal subtle features such as tiny, hooked branches on the spicules. The students are involved every step of the way, from collecting them to generating an electron micrograph.
