Does Scale Matter? A Multi-Scale Investigation of Unionid Species Assemblage and Microhabitat Parameter Relationships Within and Among Great Lakes Tributaries

Freshwater mussels (Unionidae) are the most imperiled fauna group in North America with over 70% of mussel species in need of conservation.  To develop conservation plans for the recovery of unionids, it is essential to increase knowledge of the current distribution of unionid populations and their habitat requirements.  Taking a multi-scale approach, we investigated the current unionid assemblages and associated microhabitat parameters within and among Michigan rivers. Using a systematic multi-scale sampling design, we sampled 1345 quadrats(1m x 1m), 495 blocks (3m x 5m), 16 sites, and 8 Michigan rivers within 3 Great Lakes drainages. An ANOVA determined fine scale differences in unionid assemblages and microhabitat parameters.  Ordination techniques (PCA and NMDS) were used to evaluate differences in assemblages and microhabitat parameters among sampling sites and a multi-response permutation procedure was applied to each ordination to investigate differences at coarser scales.  Differences in unionid assemblages were observed at each spatial scale; from the finest to the coarsest scale.  Differences in microhabitat parameters were observed at fine scales and dissolved as spatial scale increased.  This study has allowed us to recommend a multi-scale approach for future applications of unionid management strategies to successfully sustain and recover unionid communities.