RELATIONSHIP BETWEEN THE SPATIAL-DISTRIBUTION OF FRESH-WATER MUSSELS (BIVALVIA, UNIONIDAE) AND THE HYDROLOGICAL VARIABILITY OF RIVERS

Hydrological variability refers to the differences in the patterns of flow among rivers. Drainage basins in southwestern Ontario and southeastern Michigan were selected a priori using records of flow variability. Hydrological variability was then used as a macrohabitat measure of mussel habitat. The distribution and relative abundance of mussels were determined in drainage basins of two hydrologically different types, three event responsive (i.e., hydrologically flashy) and three stable (i.e., hydrologically stable). Eleven event and 10 stable sites were sampled once each from 18 to 30 August 1993. Fifteen species of unionids were found in the study area (13 in event rivers and 9 in stable rivers), with different relative abundances in each regime. Multivariate analyses revealed that there are distinct mussel communities based on the hydrological variability of the river. Amblema plicata, Pyganodon grandis, and Fusconaia flava characterized event sites and Elliptio dilatata, Lampsilis radiata, and Lasmigona costara characterized stable sites. We propose that some unionids can be associated with river types with specific hydrological features and their distribution can be predicted using flow-related stream attributes.