Assemblage Structure of Freshwater Mussels (Bivalvia:Unionidae) in Rivers with Grassy and Forested Riparian Zones

Abstract

This study was designed to compare unionid assemblages in rivers with grass-dominated and densely treed riparian zones in southwestern Ontario. Environmental variables related to the riparian classes were measured at 24 sites (2 riparian classes × 3 river drainages per riparian class × 4 sites per drainage). We found 17 species in the study basins. Rivers with narrow, grassy riparian zones were characterized by Pyganodon grandis and Strophitus undulatus, whereas rivers with wider, forested riparian zones were characterised by Elliptio dilatata, Lampsilis radiata, Lampsilis cardium, and Fusconaia flava. Basin types did not differ in mean number of species per site ( $\overline{\text{x}}_{\text{grass}}$ = 3.75 (SE = 0.708); $\overline{\text{x}}_{\text{forested}}$ = 4.00 (0.670)). However, a shift towards dominance by a single species was found in grassy rivers where over 60% of individuals in these rivers were P. grandis. Riparian classes differ in physical and chemi...