Freshwater Mollusk Projects
at the Illinois Natural History Survey
Jeremy Tiemann, Kevin Cummings, Sarah Douglass, Alison Stodola

Freshwater mollusks are a vital component of stream ecosystems.  Not only does their sensitivity to habitat alterations allow them to be biological indicators of stream health, but mollusks, mussels in particular, also provide valuable ecosystem services by continuously filtering water, removing excessive nutrients and pollutants, thus aiding in cleaning and purifying creeks and rivers.  This behavior also allows mollusks to hold central positions in food web dynamics by consuming algae yet being 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 500 (~73%) of the estimated 700 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 80 freshwater snails. freshwater mollusks, photo by Kevin Cummings

The Illinois Natural History Survey (INHS) Mollusk Collection staff are involved in several freshwater mollusk projects.  First, 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.  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, and have found a snail never before collected in the state.  For non-native mollusks such as Zebra Mussel and Chinese Mystery Snail Cipangopaludina 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.

Beginning in 2005, the INHS partnered with the Illinois Department of Natural Resources, the U.S. Fish & Wildlife Service (USFWS), and state agencies in Pennsylvania and Ohio to implement portions of the USFWS’ recovery plan for the Northern Riffleshell (Epioblasma rangiana) and Clubshell (Pleurobema clava).  Both species are federally endangered and were historically present throughout the Ohio River drainage, including the Vermilion River of the Wabash.  Their range-wide declines were not attributed to one problem, but rather a combination of issues that reduced habitat and water quality, including impoundments, siltation, pollution, stream dredging, and exotic species.  A salvage project in Pennsylvania on the Allegheny River provided an opportunity for the translocation of Northern Riffleshells and Clubshells into Illinois.  The Hunter Station Bridge, which passes over the largest known populations of these two species, is scheduled for removal in 2018.  It is estimated that this bridge project would directly impact nearly 100,000 mussels.  Since 2010, nearly 4,200 Northern Riffleshell and 3,700 Clubshell have been translocated to the Salt Fork Vermilion River and Middle Fork Vermilion River. Both of these streams have multiple areas in conservation ownership and support diverse and highly-valued mussel assemblages and populations of the known fish hosts.  The goal of this project is to re-establish self-sustaining Northern Riffleshell and Clubshell populations into their historical ranges in Illinois, and to determine the viability of translocating endangered mussels displaced by bridge construction projects. This relocation project is being funded, in part, by a natural resource damage assessment settlement (Hegeler Zinc - Lyondell Basell Companies) to the USFWS and to the State of Illinois.

Our newest project involves the confirmation of two new exotic aquatic mollusks.  Corbicula has been described as a “hyper-invasive alien.”  It was first recorded in North America in the western United States nearly 90 years ago and breached the Continental Divide in the late 1950s. Since then, it has spread throughout the United States and into Mexico.  Established populations have yielded millions of dollars in damage to industry and infrastructure, and removal costs are estimated at more than a billion dollars annually.  The Midwest has long been recognized as having only Corbicula fluminea. However, in 2008, a tentative second species, Corbicula largilllierti, began appearing in the navigable rivers in Illinois. Then, in 2015, a third Corbulid species was discovered in the Illinois River. This indeterminate and undocumented Corbulid might represent a novel invasion in North America, and could be a substantial threat if it were to spread.  In collaboration with the University of Michigan - Museum of Zoology, genomic and morphometric assessments are being employed to confirm the identity of this potential new invader and the confirmation of C. largillierti.  We currently are seeking funds to help in our efforts of this project.  Given the substantial ecological and economic impacts of invasive Corbicula, rapid detection, identification, and adaptive management development is critical in attenuating spread and, ultimately, minimizing the environmental and economic damage. We request that our colleagues to please alert us to the presence of unusual Corbulids in your study areas if encountered.

We believe it is important to continue the basin surveys by the SWG-funded freshwater mussel crew to help identify resource rich waters in Illinois and document changes in the fauna. Future funding for this project is unclear but hopefully a solution will be found. We hope we can count our your support to help continue this important work.