Freshwater mussel assemblage structure in a regulated river in the Lower Mississippi river Alluvial Basin, USA
1. This paper documents a diverse, reproducing freshwater mussel community (20 species) in Lower Lake } an impounded, regulated portion of the Little Tallahatchie River below Sardis Dam in Panola Co., Mississippi, USA.2. Despite being regulated and impounded, the lake has a heterogeneous array of habitats that differ markedly in mussel community attributes. Four distinct habitat types were identified based on current velocity and substrate characteristics, representing a gradient from habitats having lotic characteristics to lentic habitats. All four habitat types supported mussels, but habitats most resembling unimpounded, lotic situations (relatively higher current velocity and coarser substrate) had the highest mussel abundance and species density (10.1 mussels m-2 , 1.8 species m-2 , respectively). Lentic habitats (no flow, fine substrate) were characterized by lower abundance and species density (2.0 mussels m-2 0.8 species m-2, respectively), but supported mussel assemblages distinctive from lotic habitats.3. Evidence of strong recent recruitment was observed for most species in the lake and was observed in all four habitat types.4. Although impounded and regulated, Lower Lake represents one of the few areas of stable large stream habitat in the region. The presence of a diverse, healthy mussel community in this highly modified habitat suggests that a large component of the regional mussel fauna is relatively resilient and adaptable and is limited primarily by the absence of stable river reaches. Management actions that increase stream stability are likely to result in expansion of the mussel fauna and restoration of a valuable component of ecosystem function in this region.