Mussels are long-lived animals meaning they can live for several decades and in some instances a century or more. They often live in multi-species communities called mussel beds. These beds can support 30 or more species and are generally more diverse in rivers and streams than in lakes.
Mussels spend most of their life in a small area of the lake or stream bed that they inhabit. However, they do have the ability to move around with the use of their muscular foot. Mussels insert their "foot" into the sand or gravel and pull themselves forward, inching their way along the bottom. This enables them to escape slowly falling water levels and to search for preferred habitats in which to live.
In order to survive, mussels must gather food and oxygen from the water. They do this by drawing water in through their incurrent siphon, moving the water over their gills, and then passing the water out through their excurrent siphon. Oxygen is absorbed through the gills, and food in the water, mostly particulate organic matter and phytoplankton, is carried to the mussel's mouth by tiny hair-like cilia located on their gills (mussel anatomy image).
Freshwater mussels have a complicated life history that is tightly linked to freshwater fishes. Males release sperm into the water that are drawn in by the females. The fertilized eggs are brooded in the female's gills, where they develop into tiny larvae called glochidia. The glochidia are then released by the female mussels and attach to fish gills or skin as temporary parasites. Over a few weeks to several months the glochidia develop, or metamorphose, into juvenile mussels while attached to the host fish. When this process is complete the juveniles detach from the host, fall to the lake or stream bed, and begin their lives as free living mussels. Some freshwater mussels require one particular species of fish as a host for their larvae whereas others may use many. One mussel species, the salamander mussel, is very specialized in that it only uses the gills of an amphibian, the mudpuppy, as its larval host. Attaching to a host is also the primary way that mussels are distributed throughout a water body; therefore, a mussel species' distribution is directly related to the host fish's distribution.
To improve the larvae's chances of contacting a suitable host, many mussel species have evolved elaborate methods to lure fish to the pregnant females. Females display and actively move their mantle lures to attract the host. When a fish strikes the lure glochidia are released and attach to the fish. The plain pocketbook has a modified mantle flap that mimics a minnow to attract predator fish like the largemouth bass (see video). Other mussel species package their developing glochidia into cases called "conglutinates." These conglutinates may resemble insects on which fish normally feed. When a fish attempts to eat this "imposter insect" the fish becomes infected with the mussel's glochidia.