Watershed Toolshed

Freshwater Mussels: Ohio's Panther

Ohioans may not have panthers, those sleek endangered cats that Floridians have, but we do have our own intriguing, and elusive group of endangered species--our native freshwater mussels. Unknowingly, you've probably canoed over them, in their gravel stream bottom home, not stopping to consider how they got there, or that researchers report them to be on the brink of a regional catastrophic extinction event.

One species, the Northern Riffleshell (Epioblasma rangiana), is currently on the Federal Endangered species list, along with 68 other species of bivalves considered endangered or threatened (researchers believe more should be added). It is a state endangered species in Ohio, Indiana, and Michigan. And has been eliminated entirely in Illinois.

The Life Cycle of Freshwater Mussels

Freshwater mussels need host fish to complete their life-cycles. Their unique larvae, known as glochidia, are released near enough to a fish to piggy back a ride onto its fins and gills. Fish that can serve as a host (by not rejecting the larva) will encapsulate them and allow them to mature into juveniles. After a few weeks, the young mussels drop off , and dig in and prosper -- if they land on a suitable substrate.

Although extinction of freshwater bivalves has only recently begun to be recognized, the extinction has been happening since at least 1900 according to Arthur Bogan, curator at North Carolina State Museum of Natural Sciences. Bogan also points out that if all the endangered mussels disappear in the next 100 years, of the 300 or so species in North America 54% will have become extinct.

One person who doesn't want this to happen is Tom Watters, senior researcher with the Department of Evolution, Ecology, and Organismal Biology at the Ohio State University. Tom points to the decline of the Northern Riffleshell as a classic example, like many of the endangered mussels of the North Amercia, of a species that relies on a habitat that is vanishing: the strong currents and hard river bottoms of the gravel riffle.

One of the greatest causes of mussel decline (and there are many including: excessive siltation, over-harvest, and the presence of zebra mussels) appears to be the damming and impoundment of rivers. Many species of fresh water mussels are simply adapted only for riffles of large rivers -- and, once dammed, that habitat is lost: silt can not be carried away, host fish often die or leave, and the once highly oxygenated water becomes oxygen deficient.

The OSU Division of Molluscs has 3 on-line databases to help you learn more about mussels and streams:

• Mussel/Host - This database allows the user to:
  - search for hosts of a particular mussel species, genus, or family
  - search for mussels (parasites) of a particular host species, genus, or family
  - search for a particular author
  - combinations of the above
• River Basin Drainage - This database may be used to identify tributaries of a system or give the drainage pattern for a given water body.
• Bivalve - This is a searchable FileMaker Pro database of the specimens in the Bivalve Collection at the OSU Museum of Biological Diversity, one of the largest collections of freshwater bivalves in the world. Many of the records deal with rare and federally endangered species.

Additional References

On-line Field Guide

Cummings, K.S., and C.A. Mayer. (1992) Field guide to freshwater mussels of the Midwest. Illinois Natural History Survey Manual 5. 194 pp.

Research

O'Dee, S.H. & Watters, G.T. (2000) New or confirmed host identifications for ten freshwater mussels. Proceedings of the Conservation, Captive Care, and Propagation of Freshwater Mussels Symposium, 1998. pp. 77-82. (pdf)

Watters, G.T. (2000) Freshwater mussels and water quality: a review of the effects of hydrologic and instream habitat alterations. Proceedings of the Conservation, Captive Care, and Propagation of Freshwater Mussels Symposium, 1999. pp. 1-14. (pdf)

Watters, G.T. (2001) The evolution of the Unionacea in North America, and its implications for the worldwide fauna. In: Bauer, G. & K. Wachtler, eds. Ecology and Evolution of the Freshwater Mussels Unionoida. Springer Verlag, Berlin. pp. 281-307.

Watters, G.T. (2002) The kinetic conglutinate of the creeper freshwater mussel, Strophitus undulatus (Say, 1817). Journal of Molluscan Studies, 68, pp. 155-158. (abstract with link to pdf)

Watters, G.T. & O'Dee. S.H. (2000) Glochidial release as a function of water temperature: beyond bradyticty and tachticty. Proceedings of the Conservation, Captive Care, and Propagation of Freshwater Mussels Symposium, 1998. pp. 135-140. (pdf)

Watters, G.T., O'Dee, S.H. & Chordas (III), S. (2001) Patterns of vertical migration in freshwater mussels (Bivalvia: Unionoida). Journal of Freshwater Ecology 16: 541-549.