Freshwater Mollusks

Freshwater_mussels_collected_in_IllinoisFreshwater mollusks are a vital component of stream ecosystems.  Not only does their sensitivity to stream habitats allow them to be biological indicators of stream integrity but they also occupy a central position in food webs by grazing on periphyton and providing a food source for predators.  Sadly, freshwater mollusks are one of the most imperiled groups of animals in North America.  At least 210 (70%) of the nearly 300 freshwater mussel species and over 260 (40%) of the estimated 650 freshwater snail species are extinct, are listed federally as endangered or threatened, or are in need of conservation status.  The primary factor responsible for the decline is anthropogenic disturbances to stream habitats (e.g., habitat destruction and environmental contamination), commercial harvest, and invasion of exotic species (e.g., zebra mussel Dreissena polymorpha).  The decline in species richness also is evident in Illinois.  Two-thirds (53) of the 80 freshwater mussel species are extirpated from the state, are listed at the state-level, or have relatively unstable populations, but not much is known about the status of the state’s 76 freshwater snails.

 

Updating Status of Mollusks in Illinois

Collaborative efforts between the INHS and the Illinois Department of Natural Resources (IDNR) are underway to update the current status of freshwater mollusks in the state.  Since 2008, we have begun capturing freshwater mollusk data by visiting natural history museums (e.g., the Field Museum of Natural History, Chicago) and conducting field surveys throughout the state that typically correspond with predetermined IDNR fisheries and Illinois Environmental Protection Agency basin survey sites. Natural history museum collections represent a unique and invaluable source of data on the distributions and historical occurrence of Illinois freshwater mollusks, whereas current surveys provide data on changes in assemblage structure, population declines, and shrinking distributions that is occurring in the state. 

 

Ornate Rocksnail

The efforts thus far have been highly successful for both native and non-native freshwater mollusks.  For native species, we have documented several new basin records, including one for a federally endangered mussel (fat pocketbook, Potamilus capax), and have found a snail (ornate rocksnail, Lithasia geniculata, pictured left) never before collected in the state.  For non-native mollusks such as zebra mussel and Chinese mystery snail Bellamya chinensis, we are witnessing their distribution moving towards more inland waters (e.g., 3rd and 4th order streams), probably as a result of human use (e.g., canoeing or aquarium releases).

 

 

The data we collect will assist natural resource agencies by filling knowledge gaps in the Illinois Comprehensive Wildlife Conservation Plan and Strategy, assisting water quality initiatives, guiding restoration and conservation initiatives, and aiding the Illinois Endangered Species Protection Board in determining the state status of rare freshwater mollusks.