Ken Baker: Efforts underway to save mussels in an Ohio river

Mucket, fatmucket, and purple wartyback. Elktoe, giant floater, mapleleaf, fluted-shell, and pocketbook. In all, 204 animals and eight species, with an average age of about 8 years (maximum 15).

I’d been invited to observe biologist Jeff Gordon (a former student) and his three assistants working on a freshwater mussel search-and-relocate project in a shallow stretch of the Sandusky River by a bridge scheduled for a significant upgrade next year. Their assigned task was to find and remove to a safe, upstream location every adult mussel they could find in the section of the river that would likely be impacted by work on the structure.

“Every adult mussel” translated into 15 hours over two mid-August days in neoprene wetsuits bent over Aqua Scope underwater viewers and noodling with bare fingers through each square foot of the river’s cobbly bottom.

All that work to move a bunch of clams. Why bother?

A. Mussels are not clams, even though they are often called freshwater clams. It’s true that both groups are members of the taxonomic Class of mollusks called Bivalvia (“two valves” referring to the shells protecting the body). But they differ in a number of important ways, one of which is the mussels’ extraordinary method of reproduction.

B. And yes, by God, those 204 animals more than merited the effort to save them from potential destruction by the upcoming bridge modifications.

Freshwater mussels are being threatened

Some think of mussels as the freshwater counterpart of marine clams, but it’s not that simple since a number of clam species occupy freshwater habitats. One problematic example is the highly invasive Asiatic clam (Corbicula fluminea) that has cost billions of dollars in damage by clogging water intakes and other submerged infrastructure.

Almost all of our mussels belong to the Unionidae Family. Prior to European colonization, the rivers, streams, and lakes of North America were home to more than 300 species of Unionid mussels. Of these, 38 are now thought extinct, 77 are considered critically impaired and many others have experienced marked reductions in population, making freshwater mussels arguably the most seriously impacted group of animals on the continent, which is why Ohio State Code prohibits their collection without a permit.

Unionid mussels, like clams, are filter feeders, meaning they obtain their food (and oxygen) by pulling water into the chamber between their shells (via an incurrent siphon) where bits or organic matter and plankton are removed from the water and ingested. The nutrient-stripped water is then ejected (via an excurrent siphon).

And therein lies the source of both the mussels’ ecological value and their susceptibility to industrial and agricultural pollutants, siltation caused by eroding soils from deforested river banks, and competition with invasive species such as zebra mussels.

A mussel filters 8 to 15 gallons of water daily

Individual Unionid mussels have been reported to filter between 8 and 15 gallons of water per day, removing detritus and pollutants from the water column in the process. One study conducted by researchers at Central Michigan University found the Unionid population in a section of the Kalamazoo River collectively filtered some 2,600 gallons of water every day.

But excessive erosion of soils from denuded river banks can overwhelm and clog a mussel’s water filtering systems, a problem compounded by the widespread damming of flowing waters to make placid reservoirs. And in polluted waters, mussels’ filter feeding behavior can lead to the buildup of toxic compounds in their tissues.

Then there’s the accidental introduction of zebra and quagga mussels (from ballast water released by European freighters) which effectively eliminated once rich beds of Unionids from the shallow areas around the islands of Western Lake Erie. Hundreds of the tiny mollusks would cover a Unionid’s shells, stripping the water of its nutrients before reaching the larger mussel’s incurrent siphons.

In many scuba-based research dives in the area between 1996 and 2006, I saw thousands of Unionid shells but never a living Unionid. And let’s not forget about buttons.

The button industry over-harvested mussel beds

In 1916, 40 million “pearl” buttons punched out from the inner lining of freshwater mussel shells were produced by a workforce of some 20,000 people employed by dozens of companies throughout the Midwest. And yet, by the mid-1930s, the industry was dead — largely killed by over-harvesting of mussel beds.

So, reproduction in freshwater mussels. If you’ve got four minutes, take a look at the YouTube video, youtube.com/watch?v=I0YTBj0WHkU. What you’ll see is a few examples of how a lot of Unionids use minnow-shaped lures (made of soft tissues from inside their shells) to draw predatory fish near enough to shower them with tiny larvae called glochidia.

Glochidia look all the world like miniature castanets with fangs. Once inside a host fish’s mouth, they spring shut on its gills where they will feed like vampires on the host’s blood for several weeks before dropping off to start their lives as baby mussels on the river or lake bottom.

Not to worry. The glochidia are so minuscule they seldom do much harm to even a small host fish.

Ken Baker is a retired professor of biology and environmental studies. If you have a natural history topic you would like Dr. Baker to consider for an upcoming column, please email your idea to fre-newsdesk@gannett.com.

This article originally appeared on Fremont News-Messenger: Ken Baker: Efforts underway to save mussels in an Ohio river