Relationship between physical environmental factors and presence of molluscan species in medium and small river estuaries

River estuaries are critical aquatic environments characterized by large environmental gradients in their water quality, riverbed material, and microtopography in the longitudinal and transverse directions. Molluscan fauna are sensitive to changes in water quality or bottom sediment conditions, and include species that inhabit unique environments or have a high capacity to thrive in different habitats. The interrelations between ecology and whole physical environment of molluscan fauna have rarely been studied, especially in medium and small sized river estuaries. This study was conducted to investigate the relationship between molluscan fauna and multiple hierarchical physical factors in river estuaries, and develop a prediction model for each of the molluscan species under study. The study focused on molluscan fauna in river estuaries in medium and small size rivers, where knowledge is particularly limited. Results obtained from quadrats were classified into three groups related to physical factors, including wave and river energy and habitat scale factors. Prediction models for molluscan species indicated that physical factors affected different species at varied scales. There were species influenced by watershed scale, habitat scale, or both. Because the physical factors influenced species at different scales, prediction of potential molluscan fauna on a site is also critical, in addition to the conservation or restoration of habitats.