Page 17 - The Freshwater Mussels of Oklahoma

CONSERVATION

The freshwater mussels of North America are one of the richest species groups of
aquatic animals. There are approximately 300 recognized species in the continental
United States and with the advent of DNA technology, more will probably be added to
the list. However, the same ecological, anatomical, behavioral and reproductive factors
that have resulted in this diversity of species have also contributed to their dramatic
decline. Almost one in four species is considered endangered or threatened. In
Oklahoma, populations are not as bad as most other states but there are some major
concerns. Of the 55 species that have historically occurred in the state, only one species
is extirpated (Cyprogenia aberti) and two others (Ligumia recta and Alasmidonta
marginata) are probably extirpated. All three species still exist in other states. Two
other species (Arcidens wheeleri and Lampsilis rafinesqueana) are species of very
restricted range and pose special problems in trying to maintain populations within the
state. These and all the other species within Oklahoma are subject to a variety of threats
to their success, some of which are unique to being a mussel and others imposed upon
them by the vagaries of man and nature. Factors affecting freshwater mussel populations
in Oklahoma fall within several categories, including the following:

Immobility: Because of the relatively stationary life style of freshwater mussels,
this requires that for a female to reproduce, there must be a male source of sperm either
nearby or upstream. This relative immobility also makes it difficult or impossible to
escape events that may impinge on their health, well-being or reproduction.
Parasitism: Because freshwater mussels require a period of parasitism on a fish
host, this means that in order to successfully transfer glochidia from the stationary gravid
female to a proper fish host, she must attract the fish in some manner and release the
glochidia at the proper time. Success of this part of the reproductive process is also
dependent on the presence of the proper fish host species. Changing fish faunas in our
lakes and rivers are potentially serious impediments to the reproductive potential of some
mussel species.
Location: Mussels are benthis organisms, that is they live in the bottom substrate
of aquatic ecosystems. The most favorable substrates are gravel or stable sand or mud.
Shifting sand, fine silt, soft mud or organic debris are generally unfavorable for all but
the most mobile species. Numerous factors to be discussed further on have dramatic
effects on benthic substrates. Also, the substrate itself may become the repository of
toxic substances such as heavy metals, pesticides and herbicides that remain in the
substrate more or less permanently long after its deposition.
Feeding: Mussels are filter feeders. Water along with organic nutrients are
siphoned through the mantle cavity and gills thus exposing these delicate and permeable
tissues to anything present in the water column. Chemicals that may be concentrated in
plankton and organic particles and taken in by mussels may be further concentrated.
Anoxia: During periods of drought or low water levels, especially during high
summer temperatures, oxygen levels may plunge to dangerously low levels. This can be
exacerbated by eutrophic conditions due to evaporative concentration of nutrients or the

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