Effects of severe drought on freshwater mussel assemblages

  • Author(s): Hagg, Wendell R.; Warren Melvin L., Jr.
  • Date: 2008
  • Source: American Fisheries Society 137:1165-1178, 2008
  • Station ID: --


We examined changes in freshwater mussel abundance and species composition at eight sites in Alabama and Mississippi in response to a severe drought in 2000. Five small-stream sites in Bankhead National Forest were heavily impacted by drought; one site dried almost completely, and four sites experienced total or near cessation of flow but retained water in their channels to a large extent. In contrast, three large-stream sites retained flow and experienced only minor streambed exposure, primarily along the stream margins. In small streams, overall mussel density before and after the drought declined by 65-83%, and the magnitude of the decline did not differ among streams regardless of whether the channel dried or remained wetted. Introduced Corbiculafluminea (Asian clam) experienced near total mortality and declined to a greater extent than native unionids. The magnitude of decline was similar among unionid species, and the likelihood of surviving the drought was mostly a function of predrought abundance; differences in drought tolerance among species were not evident. Consequently, assemblage composition changed primarily because of the loss of rare species, resulting in drainagewide homogenization and convergence on a shrinking species pool. In contrast, we found no evidence for changes in the total abundance or composition of mussel assemblages in large streams that continued to flow during the drought. Our results show that mussels are highly sensitive to the secondary effects of drought-most likely the low levels of dissolved oxygen caused by low flow, wann temperatures, and high biological oxygen demand-in addition to the direct drying of their habitat. The postdrought abundances of some species in Bankhead National Forest may now be below the minimum necessary for successful reproduction. These populations, which are isolated by reservoirs, may be in a downward spiral from which they will have difficulty recovering in the absence of immigration.

  • Citation: . . Effects of severe drought on freshwater mussel assemblages. American Fisheries Society 137:1165-1178, 2008.

Pristine Version Available

An uncaptured, or “pristine” version of this publication is available. It has not been subjected to OCR and therefore does not have any errors in the text. However, it is a larger file size and some people may experience long download times.

Download “Pristine” Publication
(PDF; 2.0 MB)

Requesting Publications

You can order print copies of our publications through our publication ordering system. Make a note of the publication you wish to request, and visit our Publication Order Site.

Publication Notes

  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
  • Our on-line publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unuseable.
  • To view this article, download the latest version of Adobe Acrobat Reader.