September 2023 Natural Mystery Answered

Last month’s natural mystery asked you to identify what made a furrow in the sand. Three of you sent in correct answers—one answer even included a video of this sign being made. Congratulations to Catherine Zimmer, Tom Young, and Alan Holzer for correctly interpreting this groove in the riverbed.

As Allan writes, “this is the trail of some species of freshwater mussel.”

Alan goes on to say, “as sedentary filter feeders, adult mussels don't generally move much, but they can if they need to.” But as Catherine notes, “the drought lowering of the water levels in the river likely induced mussels to move to deeper areas.” Tom notes that mussels will also make these “somewhat random looking trails as they siphon thru the bottom layer for food.”

Alan offered us a few tips to help identify these trails, writing:

"The width of the trail with no footprints off to the sides, the meandering nature of the trail, and the fact that it is in very wet sediment near the water's edge in a drought year are all good clues."

Tom notes that “mussels usually only live in relatively unpolluted water,” and shared this video he produced of mussels in action on the St. Croix river.

Thanks to everyone who sent in an answer, and congratulations again to Alan, Catherine, & Tom.

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