I used to think clams were boring, but that was before I learned about their reproductive life cycle. I formerly thought of bivalves as inactive organisms that live on aquatic bottoms like a dead stick in the mud. It’s true most species of freshwater mussels are sedentary life forms, filter-feeding on the microscopic algae and bacteria that are carried their way by currents. The males and females are even incapable of approaching each other to mate. Instead, the male ejects sperm into the water and the female takes it in while filter feeding, thus fertilizing her eggs. Amazingly, the female tricks more advanced creatures into helping spread her larva. Some species of mussels have a fleshy protuberance that resembles a worm or small minnow. When a fish strikes at the bait, the female mussel squirts her larva onto the fish’s gills. Eventually, the larva develop into little mussels and drop to the bottom of a river or lake and burrow into the mud where they’ll probably live for the rest of their lives. Other species of mussels release bags that resemble myriads of tiny aquatic insects. A fish striking the bag releases hundreds of larva which attach themselves to the fish’s gills. Biology majors seeking a subject for a master’s thesis take note–little is known about which mussel species parasitize which fish species, so the field of study is wide open.
Life cycle of a freshwater mussel.
Elliptio complanata–Eastern elliptio. This widespread freshwater mussel occurs in almost every river system in Georgia. It’s quite edible. I’ve never eaten one, but I picked up a dead one not long ago and the inside looked and smelled just like an oyster. It left a carrion-like odor on my hand, however, indicating it had gone rotten.
The Altamaha Spinymussel–Elliptio spinosa. This endangered species only inhabits the Altamaha River.
Top: Anodonta grandis–Giant Floater…Bottom: Villosa dumbelis–Eastern Creekshell
Rayed Pink Fatmucket–Lampsilis splendida
Anodonta imbecilis–Paper pondshell
A great variety of mussel species live in Georgia’s waters–the exact number is probably unknown. There’s an estimated >126 species from at least 16 genera, though many are in danger or have succombed to extinction. Mussels live a long time–up to 100 years. Nevertheless, many species are endangered. Dams, sedimentation, pollution, and the introduction of invasive Asiatic clams and zebra mussels have all reduced the amount of available habitat. Before Europeans colonized North America mussels were an abundant food source for the Indians. Georgia’ s rivers used to be crystal clear for most of the year, except during summer when Indians burned the woods, and they became black with ash (a practice they engaged in every year). Today, Georgia’s rivers are clogged with agriculturally eroded mud. This is not good for filter-feeders.
Surprisingly, I found no information about Pleistocene-aged freshwater mussels in Georgia on the web. Mussel shells are as durable as bone and should be present in alluvial fossil sites. I suspect they’ve been ignored or unnoted because scientists don’t know whether specimens associated with alluvial fossil bones are from the present or the Pleistocene. Leisey Shell Pit in Florida is a famous fossil site noted for bivalve shells, but these are sea shells, dating to when the site was under ocean water. Nevertheless, freshwater mussels were certainly abundant in Pleistocene freshwater environments throughout the south. Most were probably the same species that today are heading for extinction.