Imagine you had to live buried to your neck in sand and gravel on the bottom of an Indiana stream. You eat by filtering food from passing water. Although you can move short distances with the use of a single foot, you are mostly immobile. A hungry muskrat could snatch you at any second. If a chemical spill or plume of suffocating silt flows over you, your only recourse is to clam up, bury deep into the substrate and hope for the best. To reproduce, a female must be in close proximity and just downstream from a male. Furthermore, a specific species of fish must swim by to act as a host for your parasitic young. If this doesn’t sound like the life for you, then you would not want to be a wavyrayed Lampmussel, one of Indiana’s freshwater mussels.
The wavyrayed lampmussel is a medium-sized mussel with a rounded shell. It measures about 3.5 inches in its adult stage. It is yellowish-green and has numerous wavy rays that cover its shell.
For the wavyrayed lampmussel, the smallmouth bass is the preferred host fish. The wavyrayed lures the unsuspecting smallmouth by displaying a portion of its mantle that resembles food (like a small fish, crayfish or hellgrammite). As the smallmouth bass bites at the food-mimic, the mussel blasts the smallmouth with a cloud of glochidia, which attach by hooks to the gills. They remain a harmless passenger on the smallmouth for about a month as they transform into a miniature version of the adult mussel. Once mature, they fall off and hope that desired habitat is present wherever they fall. This mussel-fish interaction is the only practical, natural means of mussel dispersal.
If the wavyrayed lampmussel hopes to survive and even increase its foothold in Indiana, the smallmouth bass; must thrive. As water quality continues to improve and smallmouth bass populations increase and expand, the wavyrayed may well ride its coattails (or gills) back to cleaner waters.
The wavyrayed lampmussel is most commonly found in clean, gravelly, medium-sized streams. It spends its life buried in the stream bottom where it continually filters the water for oxygen and the decaying organic material and microscopic plants and animals that it requires for food. Although widespread in its distribution, the wavyrayed is not common in Indiana and is currently classified as a Species of Special Concern. As a whole, freshwater mussels are one of the most endangered groups of animals in Indiana. Of the 77 native species, at least 16 are no longer found live, 11 are classified as Endangered, and 7 as Species of Special Concern.
Status: Species of Special Concern
Reasons for the decline of the wavyrayed lampmussel and other Indiana freshwater mussels are diverse. Water pollution has negatively affected freshwater mussels, probably even more than other aquatic organisms. Mussels are highly sensitive to chemical and organic pollutants. Nonpoint source pollution and siltation has suffocated mussels. Habitat alterations, such as dam constructions, have eliminated critical habitats and blocked mussel (and their fish hosts) movements. Mussel harvest for the button and cultured pearly industry may have reduced some populations. Introduction of the exotic zebra mussel has also had a major impact. By attaching directly to the native mussel’s shell, masses of zebra mussels block the mussel’s ability to filter water, and in many cases eventually kill the native mussel.
Even as conditions improve in a stream that once supported a healthy mussel population, recolonization is hampered by the mussel’s lack of mobility and reproductive strategy. Freshwater mussel reproduction is complicated and offers several opportunities for failure. First, there have to be enough males and females in close proximity of each other so that as males release sperm into the water, downstream females can intake the sperm to fertilize their eggs. After fertilization, the immature mussels (glochidia) must then parasitize a host fish to complete the reproductive cycle. As a further complication, only a few specific species of fish will work as hosts for most mussel species.