Freshwater Mussels

Class: Bivalvia
Subclass: Palaeoheterodonta (freshwater bivalves)
Order: Unionoida
Family: Unionidae & Margaritiferidae (pearl mussels)

Mussels are among the longest-lived of all invertebrates, surviving as long as 100 years. Their reproduction is complex and remarkable. Mussels, which cannot see, must make a lure that mimics a juvenile fish, worm, snail or insect to successfully attract specific fish (or in one case a type of salamander) to serve as hosts for their parasitic larvae. Mussel larvae develop into perfectly shaped tiny mussels on their host's gills before dropping off to begin lives on their own.  Mussels and their hosts have evolved together.

Mussels are also an indicator species of water quality, and they play an important functional role in rivers by filtering water constantly as they breathe and feed. They improve water quality by filtering out bacteria, algae, and pollutants, but in doing so they accumulate contaminants in their bodies.

Mussels play a critical role in the food web because they perform this filtering service and convert an otherwise inaccessible energy source into food for animals that prey on them — fish, crayfish, amphibians, reptiles, birds, and mammals. Mussel shells provide living space for insects and plants and empty shells serve as nesting sites for small fish like darters.

Source: Center for Biological Diversity
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Life Cycle

Freshwater mussels have a unique and complex life cycle involving parasitic larvae. Most of these mussel species have separate sexes, though some species have both male and female reproductive parts. The male ejects sperm into the water which is taken in by the female where it fertilizes the eggs. These fertilized eggs move from the gonads to the gills of the mussel, where they further metamorph into "glochidia", the first larval stage.

Once the glochidia are mature enough, the female releases them into the water where they attach to the gills, fins, or skin of a host fish. The glochidia feed off of the tissue of the fish for several weeks or months before they fall off as juvenile freshwater mussels and then bury themselves in the sediment. This unique life cycle allows freshwater mussels to move upstream with the fish host species.

mussel life cycle
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Energy Web

Mussels are filter feeders, which means they suck in water through the siphon that sticks out of their shell, filter that water to extract the nutrients they need to survive, and then pump the filtered water back out through another siphon. It's estimated that one mussel filters as much as a bathtub of water per day in order to get the nutrients it needs to survive. As such prolific filters, freshwater mussels play an important role in maintaining water quality and clarity. It also means they're extra sensitive to whatever is suspended in that water.

Habitat

In order to thrive, freshwater mussels like cool, flowing water and a relatively sandy or rocky bottom so they don't bury their siphons in the mud. Though we don't really think of mussels as being mobile, species that have particular host fish that spawn up upriver also require unobstructed rivers to complete their natural range.

 

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You should have a pretty good idea of what your species needs in its environment to be healthy and vibrant. Do you know if your watershed is healthy for your species?