Publication Date

12-1-2007

Degree Program

Department of Biology

Degree Type

Master of Science

Abstract

Despite the importance of crayfish in aquatic systems there are major issues threatening their conservation, including invasive species, habitat alterations, and species with small distributions or have limited geographical ranges. There is limited information regarding native range, habitat requirements, life histories and biological interactions between crayfish species. In order to examine the relationship between lotic crayfish assemblages and environmental variables at both the watershed and reach scales, data were collected from 46 stream segments in the Upper Green River Basin of Kentucky, U.S.A. An independent sample t-test compared crayfish densities between segments with gravel - small cobble, and large cobble - small boulder substrates and revealed non-significant differences for both all and large (>15 mm) carapace length individuals. Correspondence analyses were conducted separately for gravel-cobble and cobble-small boulder segments and large boulder segments and some species showed strong associations with each other. In the gravel-cobble/cobble-small boulder segments a series of one-way ANOVA's showed significant effects of sub-basin location on both crayfish density and species richness whereas in the large boulder segment there were no significant differences. An exploratory canonical correspondence analysis in the forward selection procedure was performed to reduce the number of environmental variables in the gravel-cobble/cobble-small boulder segments and large boulder segments. The second CCA performed between crayfish species and environmental variables showed relationships with several environmental variables in the gravel-cobble/cobble-small boulder segments. Significant variables elucidated were summer mean temperature, depth, and total phosphate. The second CCA in the large boulder segment, however, failed to find strong relationships between the crayfish and environmental variables. Further testing using multiple linear regression stepwise forward selection analysis demonstrated that crayfish were responding to total phosphorous, % riffle, %run, gravel, cobble, boulder, total phosphorous and ammonia in the gravel-cobble/cobble-small boulder segments. The results indicated that stream size gradient and not % land use were linearly related to both diversity (richness) and density.

Disciplines

Animal Sciences | Medical Sciences

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