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Tuesday, February 7 • 2:00pm - 2:20pm
Symposia Session - S8: Fate of Freshwater Mussels. Effects of Dreissenids on Unionid Communities in the Mississippi and Ohio Rivers

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AUTHORS: Heidi L. Dunn, Ecological Specialists, Inc.; Patricia Morrison, U.S. Fish & Wildlife Service, Ohio River Islands National Wildlife Refuge; Janet Clayton, West Virginia Division of Natural Resources

ABSTRACT: Dreissenid mussels invaded Midwestern rivers in early 1990’s, following navigation routes from the Great Lakes down the Illinois River and into the Mississippi and Ohio Rivers. They have steadily moved upstream with commercial traffic and are part of the riverine ecosystem in Midwestern commercially navigable rivers. They encrusted unionids in the lower and upper Ohio River by 1994 and 1998, respectively. Unionid encrustation in the Mississippi River occurred in the lower pools before 1995 and upper pools in 1998/1999. Fearing unionid extirpation from big rivers, Dreissenid infestation spurred regulatory agencies to consider moving unionids into refugia and developing monitoring and propagation programs. Initial unionid community monitoring revealed significant mortality in beds heavily infested with Dreissenids. At six sites monitored in the Ohio River, Dreissenid infestation increased from 1994 to 1999, from < 100 per square meter to over 25,000 per square meter. In late August 2000, they appeared to crash riverwide. However, unionids are better adapted than Dreissenids to drought and flood conditions, and many can burrow below Dreissenid encrusted substrate. Dreissenid abundance generally declines in late Spring (perhaps due to high water velocities) and continues at a low level through summer months (perhaps due to high water temperature). Juvenile settlement is noticeable in the fall, and infestation of unionids is generally highest in early Spring. No unionid species have been extirpated and mussel beds continue to persist, although at lower than historic densities. However, substrate in many Mississippi River mussel beds has changed from gravel/cobble/sand to Dreissenid shells full of silt and sand. Nevertheless, unionids are persisting in this substrate type. Unionids in unregulated rivers do not seem as affected. Dreissenids are found in smaller unregulated rivers, but typically only a few Dreissenids colonize unionids rather than the 1000s that encrust unionids in larger regulated rivers with commercial traffic.

Tuesday February 7, 2017 2:00pm - 2:20pm CST
Grand Ballroom A