European Frog's-Bit: Invasive in Cobbossee Lake
by Toni Pied
European frog's-bit (Hydrocharis morsusranae) is native to Europe and parts of northern Asia. (Click to see photos.) It's actually considered rare in Switzerland! Here in the United States, however, it is a non-native, invasive aquatic species.
This free-floating plant is stoloniferous (similar to strawberries) and can create densely tangled floating mats, crowding and shading out native aquatic plants. Dense mats may also affect wildlife, and wetlands can become completely dominated by this species. Because it floats freely, frog's-bit can spread throughout a water body by wind/wave action and by motor boats. Plants can also be broken off from a mat and dispersed via paddles and other nonmotorized boats, as well as wildlife. Once dispersed, the plants get caught up in bays, coves, and slow-moving streams.
During its life cycle, European frog's-bit may produce flowers (small, white, with three petals), but it is a dioecious plant, meaning it produces male flowers and female flowers on separate plants. Because most plants in a single colony tend to be of one sex, the plant does not often produce seeds. The main form of reproduction occurs by producing stolons (runners) that then produce a new juvenile plant. In the fall, the ends of the stolons produce turions (vegetative buds) that survive the winter by breaking off the main plant, sinking to the bottom of the waterbody, and going dormant in the sediment. In the spring, the turions float to the surface and begin growing a new plant. The leaf of European frog's-bit is leathery and heart-shaped, and only grows to about an inch to 1.5 inches in diameter.
In 2018, European frog's-bit was discovered in Cobbossee Lake. So far in 2020, this is the only known water body with an infestation of this species in Maine. It is not known how this plant was introduced. Other introductions around the country and Canada were likely due to accidental introduction via the ornamental gardening trade or from a boat carrying a piece of the plant. European frog's-bit can be found in several areas throughout Cobbossee Lake, including Weston Brook (the inlet flowing from the golf course), Horseshoe Island, Monmouth boat launch, Dismal Swamp, and several other coves on both the eastern and western shores.
What can YOU do to help, and what can YOU do if you think you see European frog's-bit? Volunteer with the Cobbossee Yacht Club Lake Association to remove frog's-bit during "Frog's-bit Fridays". These pulling sessions will be taking place throughout the summer and volunteers will work in tandem with The Friends staff. Contact Dennis Pollock to volunteer. If you see what you think might be European frog's-bit, send an e-mail to Toni Pied. Please include the location and a picture if you can.
And finally, please do your part to reduce the spread of European frog's-bit and other invasive aquatic species. Check your boat and other gear before you move from one waterbody to another. And, when you are fishing or recreating, check your motor and other equipment before moving from one spot to another to make sure you aren't dragging frog's-bit to another part of the lake. Let's work together to eradicate this species from Cobbossee Lake and prevent spread to other lakes in Maine!
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