A STUDY ABOUT HYDRAULIC CHARACTERISTICS OF UNIONOIDA UNDER FLOWING WATER

Fresh water mussels (order Unionoida) have one of the important biological roles for river ecosystems. However, abundance and habitat range of Unionoida are drastically decreasing, because of environmental change based on many artificial river works, such as over riverbed excavation and loss of floodplain habitat. There are three Unionoida species in the Matsuura river, and one lentic species (Anodouta lauta) has been dominantly decreased over the past 50 years. As they have low mobility, Unionoida are strongly affected by physical environmental change of river. In this study, we focused attention on the hydraulic characteristics of Unionoida in flowing water condition, and conducted some hydraulic experiment to three Unionoida species. The result indicated that lentic species (Anodonta lauta) was easily affected by flowing water than lotic species (Unio douglasiae nipponensis, Lanceolaria grayana). And the result suggested that hydraulic characteristic of Unionoida was one of the reason that caused a decrement of lentic Unionoida species in the Matsuura river.