Biotic and Abiotic Influences on Common and Imperiled Freshwater Mussels at Multiple Spatial and Temporal Scales with Inferences to Global Change.

PANDOLFO, TAMARA JANE. Biotic and Abiotic Influences on Common and Imperiled Freshwater Mussels at Multiple Spatial and Temporal Scales with Inferences to Global Change. (Under the direction of Thomas J. Kwak and W. Gregory Cope). Freshwater mussels are among the most imperiled faunal groups globally, and relevant ecological information is urgently needed to guide their management and conservation in the face of global change. We explored the influence of species traits, host fishes, and habitat at three spatial scales (micro-, reach-, and catchment-scale) on the detection and occupancy of 14 species of freshwater mussels in the Tar River basin, North Carolina. Detection probability for all species was 0.42 (95% CI, 0.36 –0.47) with no speciesor site-specific detection effects identified. Mean occupancy probability among species ranged from 0.04 (95% CI, 0.01 – 0.16) for Alasmidonta undulata, an undescribed Lampsilis sp. , and Strophitus undulatus to 0.67 (95% CI, 0.42 – 0.86) for Elliptio icterina. Median occupancy probability among sites was < 0.30 for all species with the exception of E. icterina, and the maximum predicted occupancy probability for 71% of the species did not exceed 0.50. Catchment-scale abiotic variables (stream power, agricultural land use) and species traits (brood time, host specificity, tribe) influenced the occupancy of mussel assemblages more than reachor microhabitat-scale features. To further investigate mussel demographics in the Tar River basin, we integrated existing survey records from 1986 – 2011 in a dynamic occupancy model. Results indicated that occupancy probability for 14 species decreased over the study period. Occupancy probability in 1986 ranged from 0.19 for Utterbackia imbecillis to 0.60 for Fusconaia masoni. Occupancy probability at the end of the 26-year study period ranged from 0.10 for Lampsilis radiata to 0.40 for F masoni. The maximum difference between occupancy probability in 1986 and 2011 was 0.30 for Alasmidonta undulata. Mean survival for all species was high (0.97, 95% CI = 0.95 – 0.99). However, the mean colonization probability was very low (< 0.01, 95% CI = < 0.01 – 0.01). These results indicate that mussels persist at sites that they have already occupied, but that they are not colonizing sites where they had not been previously. One particular threat that mussels face with global change is thermal regime alteration. We combined extensive field measurements of temperature in the stream water column and substrate at sites where mussels occur, measures of abundance and species richness for mussels and fish, and current thermal tolerance knowledge for mussels and fish to generate a comprehensive assessment of potential threats mussels face as temperatures continue to rise with global change. Average summer (June – August, 2010 – 2012) temperatures at mussel-occupied sites in the upper Tar River basin ranged 16.2 – 34.7 °C. The mean temperature from the hottest 96 h at each site ranged 23.5 – 31.5 °C. Temperature threshold exceedance durations indicated that both acute and chronic freshwater mussel thermal tolerance thresholds were met or exceeded. Another primary threat from global change is habitat alteration and degradation. We empirically measured habitat availability and microhabitat use for 10 freshwater mussel species to determine habitat suitability distributions for six microhabitat parameters. Among species, mean water depth of occupied habitats ranged 0.23 – 0.54 m, mean bottom velocity ranged 0.001 – 0.055 m/s, average mean-column velocity ranged 0 – 0.055 m/s, and mean substrate penetrability ranged 0.11 – 11.67 on an index scale. The most commonly measured dominant substrate materials were silt, sand, very coarse sand, pea gravel, and coarse gravel. The most commonly associated cover types were coarse woody debris and fine woody debris. We found a relationship between niche breadth and conservation status of a species. Federally endangered A. heterodon consistently showed a narrower suite of suitable microhabitats than the common mussel E. complanata. These findings will enhance the understanding of freshwater mussel ecology and will guide conservation strategies in the face of global change.