Macrophyte Mastery

When biologists study aquatic plants, they find a diversity of native species that creates a patchy underwater landscape. Minnesota Department of Natural Resources Senior Research Scientist Paul Radomski is among them. “A patchy field composed of many different plants creates lots of the edges, nooks, and tunnels panfish need to both hide from and pursue prey,” he says. “Multiple fish species and age-classes depend on a diversity of plant habitats for feeding, spawning, and refuge.”

Radomski’s “patchy” concept is key, for a diversity of plants suggests a balanced environment in which each species of plant offers something unique that certain invertebrates or fish require—food, habitat, or both. “We could talk a lot about native versus invasive plants,” he says, “yet of primary importance is that native plants coexist best, while invasives such as Eurasian milfoil tend to overgrow native plants, reducing the patchiness of littoral zones.”

Taking the concept a step further, he adds: “Plant diversity is highest in heterogeneous lakes. These are generally larger or deeper waters with various types of bottom substrate and more convoluted depth variations. Conversely, homogeneous lakes, which are often more turbid, host greater phytoplankton (algae) densities relative to rooted macrophytes. Ideally, you like to see an abundance of submersed plant species, because they increase the probability that at least one is winter-hardy.” But which macrophytes overwinter? Where do they grow? And when do they attract panfish?

The Jungle

Coontail (Ceratophyllum demersum)—This common macrophyte tolerates cold water and low light levels, allowing it to frequently overwinter as an evergreen. “Live winter coontail appears green and bushy, while dying stalks easily fall apart in your hand,” Radomski says. “Unlike most plants, coontail isn’t always rooted to the bottom. Instead, plant masses can drift between different depths—10 to 20 feet—on spacious flats.”

Providing nearly optimal winter habitat for bluegills and occasionally crappies, coontail creates homes for a host of invertebrates, including certain species of mayfly, caddisfly, and midge larvae—critters that make up that gelatinous goo you find in panfish stomachs.

Sometimes you get especially lucky and find swarms of scuds, little crustaceans that crave coontail salads. Likewise, bluegills pop scuds like candy, bulking up rapidly. It’s a sweet weed-prey-panfish link worth the extra detective time. While traveling the winter panfish trail, we’ve found a number of lakes housing this pattern, one that appears strongly tied to clear ponds or small lakes cut into treeless valleys and windswept prairies. The presence of scuds becomes immediately obvious, as they swarm entire plant beds.

Elodea (Elodea canadensis)—Canadian waterweed is another name for a plant anglers encounter often, though rarely identify.