Development of standardized and validated survey methods for assessing unionoid mussel assemblages in Missouri
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Unionoid mussels are a highly imperiled faunal group that play an important role in the function and health of freshwater ecosystems. Habitat alteration due to anthropogenic influences led to dramatic losses in freshwater mussel diversity, making the long term monitoring and management of these organisms a priority for state and federal agencies. Missouri contains some of the most diverse mussel beds in the Midwest, but lacks a comprehensive monitoring framework for sampling unionoid mussel assemblages. Development of a standardized and validated sampling framework is essential for collecting precise and accurate data to facilitate informed management decisions and determine the success of implemented management plans. Sampling freshwater mussels in wadeable rivers often involves visual-based survey methods subject to multiple levels of bias. A baseline understanding of the ecological, behavioral, and habitat-mediated biases associated with multiple survey techniques is crucial for validation of a standardized sampling protocol. Validating standard methods allows assessment of the comparability of data collected between sites with spatial and temporal variability in assemblage composition and habitat conditions that could bias survey results. In this thesis, I focus on developing and validating standardized sampling techniques for assessing freshwater mussel assemblage-level metrics (e.g., species richness) over a range of habitat features in mid-sized, wadeable rivers in Missouri. The primary objectives are to: 1) determine how sampling technique and habitat features affect site-scale measures of species richness; 2) determine factors that affect site-scale measures of assemblage structure; and 3) determine the effect of sampling technique on species detectability, particularly low-abundant species. Five survey methods were implemented at 14 sites throughout the Meramec River Basin, which contains some of the greatest mussel diversity in the Midwestern United States. Results suggested that an extensive, qualitative survey method (timed visual search) detected a greater proportion of mussel species with consistently higher detection rates per unit effort than more intensive, quantitative methods. Measures of mussel assemblage structure varied by method due to greater effectiveness of extensive survey methods in detecting locally rare species. However, dominant species within mussel assemblages were detected similarly across all survey methods. Under the range of conditions examined in this study, habitat variables did not substantially affect how well methods detected species present in sites; however analysis identified water depth and site size as potential sources of bias. This study represents the first step in developing a standardized, validated sampling framework and will provide agencies tasked with managing and monitoring freshwater mussel assemblages with information to assist in choosing methods that best meet their project objectives.
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