Document Type



freshwater mussels, unionids, Missouri River, Unionidea, Bivalvia, Mollusca


The lower Missouri River has historically been viewed as a fauna! barrier for unionids due to high sediment load. However this survey of the lower (channelized) Missouri River documented the presence of 14 unionid species and the exotic Corbicula fluminea (Muller, 1774). Unionids are present in stable substrates sheltered from the effects of the river's strong currents. Analysis of early literature on the Missouri River suggests reports of an absence of unionids were not based upon thorough fieldwork, and the most commonly cited rationale for their reported absence, the high sediment load in the river, is not convincing. Pre-1938 unionid vouchers from the middle Missouri River in South Dakota contradict reports of their absence in that sector, and it seems likely that a lack of thorough early field work in the lower Missouri River may explain their perceived historic absence in that sector as well. At present, substrate instability and low winter water levels preclude unionid habitation over much of the lower Missouri River, and erosion silt probably limits unionid diversity in some habitats. These same factors probably exerted similar influences upon unionids in the historic lower Missouri River, with substrate instability and low winter flows precluding establishment of any unionid populations in most Missouri River substrates, and the high silt content of the water restricting unionid diversity to a few silt tolerant species in most viable habitats.

Publication Date

January-December 2009

Journal Title

Journal of the Iowa Academy of Science





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