Exploring Our Underwater World
By Lisie Kitchel and Jesse Wienzinger, Wisconsin DNR
One of the unsung heroes in the lakes, rivers, and streams of Wisconsin are our native mussels (often referred to as clams). Living on the bottom, these creatures are often overlooked but contribute significantly to the health of our waters. Each mussel can filter gallons of water a day, removing suspended sediment and contaminants from the water column; they are nature’s power houses.
These underappreciated filter factories are important to improving water quality, but that is not all they do; they provide food for raccoons, muskrats, otters, and wading birds. Freshwater mussels also provide food for aquatic insects and crayfish when they expel what they do not consume into a gelatinous mass (called pseudo-feces) that the other aquatic invertebrates gobble up. This might seem minor, but when a mussel die-off occurs the aquatic insect and crayfish populations also decline and not from the source of the die-off. These aquatic invertebrates need mussels to make food from the water column that is otherwise unavailable to them and other creatures living on the bottom.
People often ask if you can eat mussels, and although technically you can, we do not recommend it. Also, it is illegal to harvest native mussels from Wisconsin waters. First, they are not at all palatable (based on what folks have told us), and more importantly, they are full of contaminants. Native Americans consumed mussels in large numbers, as evidenced by the shell piles near the old fish camps, but that was before modern pollutants entered our waters. Today, tribes no longer eat mussels, though the shells are still used for ceremonial purposes. The shells, with their shiny mother-of-pearl and sometimes other color interiors, are more commonly found in the water along the shoreline than live mussels. Sometimes live mussels are observed moving amongst the sand in shallow water, but most of the time these important creatures go unnoticed.
Recent droughts have also left many mussels exposed, and thousands of mussels left high and dry have been reported by concerned citizens. These mussels were often trying to reach deeper water but could not find it. If you see a freshwater mussel “stranded” out of the water that is not already desiccated and dead, you can simply throw them in deeper water.
Unfortunately, we lost far more mussels than could be saved and can only hope there are enough remaining mussels to restore those populations. The Friends of the Lower Wisconsin River set up a mussel rescue notification system to let folks know when water levels drop and mussels are at risk of being stranded. While the effort is mostly focused on the lower Wisconsin River, alerts may also include other riverways in the region.
Mussels can become stranded any time of year, but it happens most often in late summer when water levels run low. That said, sudden reservoir drawdowns, dam maintenance, or even unexpected dam failures can leave mussels high and dry at other times of the year, too.
Another under-appreciated and unique aspect of our native mussels is their complicated life cycle. There are both male and female mussels and you can tell the gender in some species by their shell shape. The males release sperm into the water column in ‘sperm balls’ which amazingly make it to a female of that same species. The fertilized eggs develop into a miniature mussel called a glochidia that is a snappy little bivalve that looks like Pac-Man®. The sole purpose of this glochidia is to get onto the gills of a fish. It needs the fish blood to complete its development. However, not just any fish will do! Some mussels have many fish ‘hosts’ that can complete their life cycle, but other mussel species only use one fish species. One particular mussel only uses the mudpuppy as a host and that’s not even a fish!
To ensure the glochidia get on the required host fish, mussels have adapted different strategies designed to attract the right fish. Many with a predatory host have developed a ‘fish lure’ as part of their soft tissues to lure the fish close enough to spit the glochidia into its mouth and subsequently onto the gills. Others release the glochidia in a kind of egg mass that looks like worms or aquatic insects and the fish eat them, allowing the glochidia to pass onto the gills. One species grabs the head of the fish and won’t let go until it has pumped all its glochidia onto the gills! These are a few of the many methods used by Wisconsin’s 52 species of native mussels. After the glochidia complete their development in the presence of the fish blood they drop off the fish and continue their existence for the next 10-60+ years, depending on the species.
All this goes on underwater, unbeknownst to most folks, so if you see a mussel, pick it up and thank it for working so hard and surviving its amazingly complicated life cycle. Then, toss it into deeper water.