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Ramshorn snail shell found
in the dry outlet wetlands |
The broad shallows at the outlet wetlands make a tempting target for exploration as January turns over into February. With much of the slumbering flora along the trail flattened by weather or equipment from the ongoing brush clearing restoration, and an afternoon silence signaling the absence of birds, this was as good a time as any to take the limited and seasonal opportunity to walk across the frozen mud and see what is normally hidden beneath water or greenery the rest of the year.
Starting from the mowed path north of the apartments, there are several deer paths to choose from leading down through the brush to the wetlands (ducking under branches and squeezing my puffy coat between dogwoods flanking the path--I am neither as slender nor as agile as a deer, clearly). My chosen path landed me at the end of the outermost arcing berm, crunching through dry reeds and rushes that take advantage of the higher ground while the cells that hold stormwater on either side of the berm were flat mud, pocked with deer and other tracks and occasional bits of stone or rotting logs.
I was on the lookout for a snail shell. The life that teems below the water's surface much of the year is a mystery, so finding evidence of mollusks while keeping my feet dry seemed like a nice adventure. It didn't take long to find: a delicate spiral, a little smaller than a quarter, resting on the frosty earth. A closer look revealed a tiny companion shell, less spiral and more conical. Both were delicate, absent the squishy residents who had previously called them home.
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| Assorted small snail shells found near the outer berm of the dry wetlands.. |
A short distance away, another mollusk: this time half of a bivalve, but again quite small (dime sized, if we are sticking with coinage as a reference). A mussel? I recalled finding many quite large mussel shells during a cleanup at the Greenway's sister site nearby, Whispering Meadows Wetland Park. Do the Greenway's wetlands support a population of mussels?
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| A tiny mussel shell found in the outer arc of the outlet wetlands. |
These fascinating invertebrates are important but often invisible parts of ecosystems, cleaning and filtering water as they feed. They rely on fish for part of their lifecycle: male mussels release sperm into the water, which find their way to females and fertilize her eggs. After the eggs develop into glochidia (larvae), they are released into the world--but they must find a fish to serve as a host for a few days or weeks, after which they will drop off and live the rest of their mussel-y lives at the bottom of a lake or stream. Some mussels can be very long-lived, thriving for many decades when conditions are right. Conditions including water quality, which we humans are doing a bang-up job of wrecking in and around our state, to the detriment of far more than mussels).
Walking slowly, looking closely. No luck encountering more bivalves within the outermost cell, I endeavored to visit the middle berm, not as easily accessible from land due to heavy thickets at either end. Crossing the low berm to reach the middle cell of the wetlands, again all was dry mud--but what was that shiny stone out there? And another....another! Big bivalves, everywhere! Or their remains, that is. How amazing that these critters can apparently thrive in our little wetlands! Perhaps the inner ponds maintain more reliable water levels than the outer arc, allowing more mussels to reach a larger size and greater numbers.
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Dozens of shiny shells could be spotted in
the middle basin of the outlet wetlands. |
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Giant Floaters can be found throughout
the Mississippi River watershed. |
A tentative ID from iNaturalist named these Giant Floaters (
Pyganodon grandis), a "short-lived" (5-10 years) freshwater mussel that can reach up to 8 inches across. They are found in calm waters throughout the Mississippi River watershed, including ponds and reservoirs as well as slower-moving rivers and streams. Their evocative common name comes from the habit of deceased individuals floating to the water's surface as they decay. Their glochidia will latch on to a wide variety of fish, including lake sturgeon and largemouth bass--though the Greenway population's host fish are probably of a humbler stature such as minnows.
When spring rains and snowmelt fill the wetlands again, we can imagine these big bivalves below the surface, silently filtering the water we sent their way. And maybe put a little effort into making their jobs easier by limiting the chemicals and other harmful runoff from our lawns and roads.
Sources/Additional Reading
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| Giant Floater with a size 9 for comparison. |
